1. business and industrial
2. energy
3. natural gas

Salt Storage Requirements in the Seneca Lake Region:
A scoping study
Authored by
Dr John K. Warren
SaltWork Consultants Pte Ltd (ACN 068 889 127)
Kingston Park, Adelaide, South Australia 5049
www.saltworkconsultants.com
i
Summary
This scoping report is written by a professional geologist, Dr. John K. Warren, who has worked and published on
salt geology for more than 35 years. His brief was to consider the suitability of salt for pressurised gas storage in the
Seneca Lake region. The report utilises relevant public data sources to draw its conclusions, which are as follows:
1) Any salt cavern to be used for pressurised gas storage should “stay in the salt.”
a) This means the cavern centred on Well 58 is probably not suitable for gas storage.
b) The nature of folding and layering within the salt in the Seneca Lake region should be better defined before any
former brine feedstock cavities are used for pressurised gas storage.
All available geological information, including core from Morton Stratigraphic Core Test well, located a few miles
north of the proposed gas storage caverns, indicate significant portions of the Cayugan salt interval are folded,
and possibly faulted. Existing seismic data in the region shows faults can both sole out in the salt or cross cut the
salt. Possible connections related to faults and fractures within and across the Cayugan salt unit need to be better
defined before former brine well cavities are utilised for pressurised gas storage. These various faults and folds
could create possible pressure leakage pathways if in “out of salt” connection with shallower units and aquifers.
c) The nature of dissolution pathways in strata above the current exploited salt levels, tied to the dissolution
of former salt layers, as well as likely timing and connections established by salt dissolution, should be better
characterised before pressurized gas storage is undertaken. This is especially urgent if the existing salt cavities
are known to be in “out of salt” situations. Fracture-prone evaporite dissolution layers are obvious in the core
from the Morton Stratigraphic Core Test Well in zones that are located tens of feet above the top of the currently
preserved salt layers . It is highly likely that similar fracture-prone dissolution breccia layers are also present in
roof strata above the current salt extent in the Watkins Glen brinefield region.
2) The integrity of old brine wells that will be recommissioned as feeders to gas storage caverns should be thoroughly investigated. The Hutchison gas explosion (see Appendix 1) illustrates problems that can be created when
a plugged and abandoned brine/cavern access well is reopened and recommissioned as a pressurised gas storage
well. The Hutchison gas escape and consequent up dip explosions offers an example of what can happen when
utilising a non-purpose designed salt cavity with re-opened access wells as feeders for pressurised gas storage.
This is especially problematic in a situation of not having a complete understanding of likely problems related to
possible out-of-salt connections to levels higher in the stratigraphy.
Likewise, the proposed use of former salt solution wells, designed for brine extraction and drilled and completed
decades ago, could create cavern/well integrity problems in the Seneca Lake region. These old brine wells would
not have utilised technology available in the construction and monitoring of modern purpose-built salt cavity
gas storage systems.
3) Clear documentation of the reliability and integrity of the salt-related geology in relation to brinefield caverns
that are planned for pressurised gas storage in the Seneca Lake region would benefit by being subject to the considerations of an independent panel of experts prior to possible commissioning as gas storage facilities.
ii
Table of Contents
Introduction 1
Part 1: Why is solution mining rock-salt different?
3
How rock-salt forms 4
How rocksalt (halite) is extracted
6
Part 2: Nature of rocksalt in the Seneca Lake region 10
Salt geology
11
Salt observations based on present or past mine operations 19
Cayuga (Lansing) salt mine 19
Himrod Mine, Seneca Lake region 20
Part3: Implications with respect to Inergy gas storage caverns in Cayugan
salt in the Seneca lake Region
Implications
28
References
32
27
iii
Introduction
This report stems from a request for a scoping study of
the general suitability of the salt geology for gas storage
in the Seneca Lake region of New York State. It was made
specifically with a request to have Dr. John Warren as
the report’s author due to his wide experience in salt
studies. Dr Warren has more than 30 years experience
in all aspects of salt geology both academic and applied.
He has authored 4 advanced-level books on the topic,
as well as numerous papers in internationally-refereed
scientific journals (www.saltworkconsultants.com).
The brief for this report is not to consider general geology of the region, but to focus specifically on what is
in the public realm related to the geology of the Salina
Group salt and its relevance to decisions of its use as
a host lithology for gas storage caverns in the Seneca
Lake region. With this in mind the report is designed
as a scoping document. Possible problems are outlined
and discussed in this report in a general fashion. The
matters raised can only be addressed if specific detailed
site geology documentation, currently unavailable, is
integrated in any possible future study.
Gas storage, via gas-filled pressurised caverns in salt,
uses cavities that are constructed by dissolution of subsurface water-soluble units at levels in the stratigraphy
composed of rocksalt and dominated by the mineral
halite. Caverns already exist in the Seneca Lake region
that were created as salt solution brine feedstock wells.
Solution wells to extract salt brine in New York State were
first drilled early last century. Unfettered brine extraction during the early days of the salt industry in places
in New York State has led to modern ground stability
problems, such as in the Tully Valley (Kappel et al., 1996).
Worldwide, halite(NaCl)-dominated subsurface intervals in rocksalt have unusual properties when compared
to most other sedimentary rocks. These near-unique
properties must be understood and planned for when
caverns are created in rocksalt and utilised for gas, fluid
or waste storage. Halite has two properties that lead to
distinctive responses when it is mined, either conventionally or via solution brine wells. First, salt is highly
soluble and so has a tendency to dissolve whenever exposed to crossflows of groundwaters; this is why rocksalt
rarely crops out at the surface and why areas above where
it lies at shallow depth are typified by natural karst and
collapse landforms. Unlike limestone and dolomite karst,
which tends to breach the surface as collapse dolines
after millennia of dissolution, cavities above rocksalt
units can rise to the surface from hundreds of metres
depth, in time frames measured in decades to hundreds
of years. Second, in the subsurface, thick beds of rocksalt
tend to flow, fold and self-heal (anneal) at relatively low
temperatures and pressures (plastic response). This is
why, when salt caverns are appropriately planned, gas
storage in salt is one of the safest methods of storing
what are highly flammable materials.
Salt flow takes place at shallow underground conditions
(even in salt mines) where other rocks tend to break,
fracture, fault and collapse (brittle response). This
combination of distinct properties creates a unique set
of responses when salt is exploited and mined. These
unique rock responses must be understood if salt is to
be safely extracted and, once the extraction processes
have stopped, the same understanding is needed for
safe materials storage in the caverns and to minimize
any associated ground stabilization problems.
Worldwide, more than 200 years of subsurface salt extraction and cavity creation/storage has shown there is
a very simple rule for any safe and successful extraction
operation and that is: “stay in the salt.” Problem areas
encountered in most salt extraction or cavity storage
operations are related to thinning or disappearing
salt seams, or where the extraction zone unexpectedly
encounters the edge of the salt body. This typically occurs in subsurface regions that also show evidence of
water-related dissolution and solution collapse in zones
above or adjacent to the salt mass. In a brine-well created cavern this typically happens where roof of wall of
the expanding cavern escapes the salt mass.
Following the concept of “staying in the salt” means
that, geotechnically, the optimum for a brine-well created cavity is: 1) a cavern constructed in a thick salt
bed with few or no internal salt layers, or better still; 2)
in a situation where the solution cavity is constructed
in a thick mass of clean diapiric salt (Figure 1; Gilhaus
2006, 2010; Warren 2006, 2015). If the salt mass being
exploited maintains structural integrity, then the weakest point, in terms of possible fluid or gas escape, is the
1
Because of the unique nature
of salt, I have divided this
scoping report into three
parts. The first summarizes
salt’s unique physical properties when compared to
other mined lithologies and
why mining salt requires an
understanding of this. This
section also mentions some
regions in the world where
Geotechnically favourable
(cavern is enclosed by salt)
Geotechnically less favourable
(cavern not fully enclosed)
well casing and cement of the
borehole used to create the
solution cavity. In the case of
a conventional mine the weak
point is the mine shaft or a
drive wherever an extraction
chamber unexpectedly leaves
the salt body and passes into
another rock type (Warren,
2006, 2015).
surface
non-salt
salt
Salt dome (diapiric)
Thick bedded salt
fau
lt
Thin bedded salt
non-salt
rock-salt
Salt breccia (tectonic)
area influenced
by cavern
cavern
a lack of understanding of
the distinctive properties of Figure 1. The position of the salt cavity with respect to non-salt strata largely controls the integrity of the salt chamber. The most geotechnically favorable cavern situations are encapsulated
rocksalt has led to subsequent in the simple adage “stay in the salt” (Gilhaus, 2010; Warren 2006, 2015).
ground instability and water
contamination. A more complete summary of problem
locations related to salt mining can be found in Warren,
2006, 2015. The most relevant chapter (Chapter 13) from
Warren 2015 accompanies this report in the Appendix 1
folder. The second part of this scoping report discusses
aspects of salt geology understanding that are directly
relevant to gas storage in the Seneca Lake region, New
York State. The report concludes (part 3) with a list of
possible problematic outcomes that must be addressed
by scientific study if pressured gas storage is to be conducted safely in the Finger Lakes region across both
the short (years) and long term (decades to centuries).
2
Part 1:
Why is solution mining of rock-salt different?
3
Sea
Brine Stage
Mineral Precipitate
Salinity (‰)
Degree Evap.
Water Loss (%)
Density (gm/cc)
Normal marine or
euhaline
Skeletal carbonate
35-37
1x
0
1.040
Alkaline earth
carbonates
37 to 140
1-4x
0-75
1.040-1.100
CaSO4
(gypsum/anhydrite)
140 to 250
4-7
75-85
1.10-1.214
CaSO4 ± Halite
250 to 350
7-11x
85-90
1.214-1.126
Halite (NaCl)
>350
>11x
>90
>1.126
Bittern salts
(K-Mg salts)
Extreme and
variable
>60x
≈99
>1.290
Hypersaline
Mesohaline or
vitahaline
Penesaline
Supersaline
Table 1. Order of evaporite mineral salts that form from an increasingly concentrated seawater (mother brine). Hypersaline is defined
as >35‰ (‰ is parts per thousand). In the degree of evaporation column, normal seawater has a degree of concentration of one.
(extracted from Warren, 2015).
How rock-salt forms
All rocksalt bodies are dominated by the mineral halite, but contain a variety of other evaporite minerals,
all precipitated during the evaporation/desiccation
of an ancient seaway, located in a former arid region
of the world. The precipitated salts typically include,
in order of crystallisation from an increasingly saline
mother brine, the following mineral sequence (Table
1): limestone-dolomite, gypsum-anhydrite, halite, bittern salts (typically magnesium and potassic salts).
Varying amounts of clays and muds (aluminosilicate
minerals) can be washed or blown into the seaway and
end up interlayered with the rocksalt and limestone/
dolomite units.
The various stacked salt layers in the Seneca Lake Region
formed in such a fashion and were originally deposited
some 417 million years ago in a shallow intracratonic
Silurian seaway or saltern. These sediments accumulated
in a foreland basin (a region of tectonic subsidence)
behind the mountains of the rising Salinic Orogenic belt
(Miall, 2008). This arid salty seaway was a hypersaline
sump, or seepage low, with a highly restricted hydrographic (surface) connection to the mother waters of
the Silurian ocean.
Most ancient marine rocksalt
bodies, including those in
the Seneca Lake region, are
dominated by the mineral
halite (NaCl). Halite is common table salt and sometimes
the terms halite and salt are
used interchangeably. But
any natural ancient rocksalt body will contain varying
amounts of the other evaporite salts, as well as large
volumes of halite. The term rocksalt describes rocks
dominated by the mineral halite.
Halite formed by seawater concentration leads to the
first unique property of any subsurface salt body containing large amounts of halite. That is, all buried salt
bodies will be susceptible to dissolution when in contact
with crossflowing groundwaters or basinal brines with
salinities that are undersaturated with respect to halite.
Undersaturation with respect to halite is the case for
most shallow groundwaters and many deeper basinal
brines. This susceptibility to dissolution is also the basis
for the solution mining of rocksalt and the consequent
creation of a cavity in the salt, which can be used for
various types of storage (solids, liquids, gases).
The second unique property of rocksalt beds and masses
is that they tend to fold and re-anneal (self-heal) rather
than break or fracture ( fault) whenever subject to superimposed stresses at shallow depths (Figure 2). Ultimately,
all rocks will fold and flow when buried deep enough
and subject to high enough pressures and temperatures.
What makes thick rocksalt layers unusual is that they
fold and flow (what is known as a plastic response) as
Window
putty
Water
25°C
Machine
oil 15°C
0.5
Honey
20°C
Bittern
25°C
1.0
1.5
Basalt
lava
Rhyolite Wet
lava carnallite
Quartzite,
Mudrock, Granite
Rock Shale
salt
Mantle
Plastic flow
6
10
9
12
10
10
1015
Viscosity (Pa s)
1018
1021
1024
Figure 2. Rocksalt’s ability to flow while other rock types tend to fracture is indicated by its
much lower viscosity at nearsurface conditions (after Warren, 2015)
4
shallow as a few tens of metres
below the surface. In contrast,
e flowage)
Bedded salt (pr
almost all other rocks remain
Bedded Salt
brittle and tend to fault/fracture (a brittle response) when
k pure bedded salt)
s burial loading of thic
Salt tectonics (require
subject to the same stresses.
Non-salt rocks typically reSalt glacier with inflating summit
Surface
(fountain profile)
main brittle until buried to
Detached
Salt
Salt
salt sheet
canopy
Salt
sheet
Salt
depths of 10 kilometres or so.
wall
Salt
Salt
anticline
pillows
roller
“Teardrop”
The ability to remain plastic
Salt
Detached
stocks
salt stock
from the time it is deposited
Salt
Diapiric salt geometries - post burial & flowage
down to more that 10 km of
(Not all bedded salt evolves in diapiric structures)
Weld
burial is due to the inherently Figure 3. Illustration of the various diapiric geometries that subsurface salt beds can evolve into
high degree of mechanical in response to loading and other superimposed (tectonic) stresses. Such deformation requires
mother salt beds to be pure and thicker than 70-100 m. This is why km-tall diapirs have never
weakness of halite/salt when formed in the Silurian salt layers of the Michigan and Appalachian Basins, but have in the Jurassic
compared to other rock types. salt of the Gulf of Mexico. Even so beds in the Salina group can show strong evidence of internal
salt flow and deformation, as described in part 2.
This also explains why salt
A distinction between storage cavities in diapiric and
beds and their internal layers
bedded salt is significant as diapiric cavities are less
can fold and flow while the adjacent beds on either side of
liable to leakage via cavity intersection with intrasalt
the salt formation can remain flat or are only broken-up
beds, which in some cases can act as fluid escape routes
by fault and fold layers that typically stop at the contact
(relative aquifers) in contact with beds above and below
with a thick salt bed. A salt bed’s ability to flow, while
the salt mass (Figure 1).
overlying beds are subject to brittle faults and fractures,
is why salt layers are sometimes informally referred to
as “crack-stoppers.”
How rocksalt (halite) is extracted
In contrast, bedded salt masses, like that in
the Salina Group in Michigan and up-state
New York, can retain more laterally continuous intrasalt beds composed of dolomite,
clays and possibly anhydrite.
Brine extraction
Conventional extraction
Salt’s ability to fold and flow, especially when the origi- Salt (halite) has two prime economic uses, worldwide the
nal mother salt bed is thicker than 50-100
m, is why salt layers in some parts of the
Shafts
Shafts
world (not the Seneca Lake region) can
deform into subvertical continuous masses
Ore skips
Ore skips
of salt known as diapir structures (Figure
Ore
3). The term salt tectonics or halokinesis
Ore
storage
Borer
storage
is sometimes used to describe this type of
mining
Drum-roller
machine
salt deformation. In the Gulf of Mexico and
mining
machine
the North Sea, such diapiric salt masses
CONTINUOUS MINING
CUT & STOPE MINING
may be up to 10-12 km tall and kilometres
wide. Internally diapiric salt masses tend to
contain few continuous non-salt intrabeds
Injection
as they have been broken up by the flowage
Evaporation
Evaporation
Pumped
of the encasing salt.
brine
Surface
Ponds
Submersible Pumps
Saline lake
Flooded
Mine
Surface ponds
SALINE LAKE BRINE PROCESSING
SOLUTION MINING
Figure 4. Salt extraction methods utilising solid rocksalt mining or salt solution
and brine processing.
5
most significant is as a feedstock to the world’s chemical industries, the other, especially in more temperate
climates, is as a road de-icing salt. Two methods are used
in regions of cool to temperate climates to obtain salt
(Figure 4): 1) Conventional underground mining, and 2)
Solution mining. A third method, involving pumping of
surface brine into huge shallow evaporation pans is not
relevant to the Seneca Lake region and is not further
considered (the largest today of these pans are purposebuilt industrial plants on saltflats along the arid coasts
of Mexico and NW Australia).
lars are dug within the salt and the mined product is
conveyed to the surface for crushing and processing.
This method requires personnel and equipment above
and below ground and the safe disposal of processed
waste material. This is the extraction approach taken
in the Cayuga Lake mine, and was the approach for
the former Himrod mine on the margin of Seneca Lake
and the now flooded and abandoned Retsof mine (see
appendix 1 for detail on the causes and history of collapse in Retsof and other salt mines with cavities that
unexpectedly ”left the salt.”
With conventional mining a shaft is sunk to the level
of the salt bed or mass and a series of rooms and pil-
Conventional salt mining takes place at depths between
250 - 1100 m (800 - 3600 ft). Any shallower and there are
Location
Timing and size
Explanations & implications
Reference
Ocnele Mari Brinefield, Romania
Partial collapse of the roof of a much
larger solution cavern occurred on 12
September 2001, it formed a large
collapse crater and forced a brine flood
down a nearby valley. Subsequent
collapse and flooding occurred on July
15, 2004.
Poorly monitored salt leaching under the former Soviet regime
between 1970 and 1993 created a gigantic cavern as salt pillars separating adjoining caverns were inadvertently dissolved
and the cavern roof migrated toward the surface. The resulting
cavern was filled with 4 million cubic metres of brine and was
more than 350 metres across. It broke through to the surface at
its northern end in 2001, with further collapse in 2004.
von Tryller, 2002
Ground subsidence
in brinefields near
Krakow, Poland
(Lezkowice/Barycz
brinefields)
At the Barycz brinefield, 33 sinkholes up
to 27 metres wide and 27 metres deep
appeared between 1923 and 1993, the
region is subject to numerous landslides.
A large deep sinkhole which was formed between 1984 and
1986 above the Lezkowice brinefield. Pollution of the groundwater system via poorly managed wells and broken pipes
allowed high salinity waters to reach the nearby Raba River. In
1983 the river salinity reached 206 mg/l.
Garlicki, 1993
Zuber et al., 2000
Collapse at
Compagnie des
Salins Gellenoncourt
saltworks near Lorraine, France
On March 4, 1998, a sinkhole more than
50 m across and 40 m deep formed atop
the SG4 and SG5 brinefield caverns,
France. It was an induced collapse.
The SG4 and SG5 caverns, drilled in 1967, unexpectedly joined
in 1971. By 1982 the salt cushion in the roof had dissolved out
putting the cavity roof in direct contact with a 25m thick marl.
In October 1992 the marls broke free, exposing a large section
of the cavity roof to direct contact with the brittle Dolomite de
Beaumont. Collapse was induced by enlarging the cavity by
injecting 300,000 m3 of fresh water.
Buffet, 1998
Cargill saltworks
collapse, near
Hutchinson, Kansas
Collapse started on October 21, 1974.
Within 4 hours the crater was 60 metres
across and after 3 days had created a
circular depression some 90 metres in
diameter and nearly 15 metres deep.
Uncontrolled brine extraction since 1888 certainly contributed
to the Cargill collapse. Post-mortem analyses showed that several warning signs, especially an enlarging bowl of subsidence,
had been noted, but ignored. After the collapse the brine field
and the loss of part of the saltworks infrastructure the brinefield
was abandoned.
Walters, 1978
Hendron and
Lenzini, 1983
Dyni, 1986
Brinefield sinkholes
at Windsor, Ontario
and Point Hennepin,
Michigan
On February 19, 1954, near Windsor, a
water filled depression some 120 - 150
metres across and up to 7.5 metres deep
formed within a few hours, destroying
much of the surface plant.
On January 9, 1971 at Point Hennepin
the first collapse crater formed, after a
few months it stabilized with a diameter
of 65 metres. A second crater developed
in April and May 1971 measuring some
120 metres across, with a depth of 35
metres.
The similarity in the geology of the Windsor and the Detroit
sites as well as the rapidity of the collapse, along with the size
and steepness of the collapse craters, led Nieto and Russell,
(1985) to question the collapse mechanism of Terzaghi (1971).
They argued his notion of steep upward caving from more than
300 to 400 metres below the surface and centred on solution
caverns in the Salina Salt could not explain the craters or their
subsidence history. Instead, they proposed a collapse scenario
based on a loss of cohesion in pressurised Sylvania sandstone
and in the presence of water.
Terzaghi, 1971;
Nieto and Russell,
1984
Retsof Mine collapse, New York
State
Loss of the Retsof Salt Mine began with
a magnitude 3.6 earthquake in the early
morning hours of March 12, 1994. Two
large, circular collapse features some
100 metres apart developed a month
apart at the land surface above two collapsed mine rooms.
Catastrophic breakdown driven by collapse of a small pillar and
panel section in the mine some 340 metres below the surface.
Collapse of the “back” was accompanied by an initial inrush
of brine and gas (methane) into the mine and by a sustained
inflow of water via the overlying fractured limestone. A month
later on April 18 an adjacent mine room collapsed. \
Gowan and
Trader, 1999;
Payment, 2000
Table 2. Collapse and subsidence events associated with brinefields (see Appendix 1 and Warren, 2015 for more detail).
6
Location
Timing and Size
Explanations and implications
Reference
Haoud Berkaoui oilfield,
near Ouarlaga,
Algeria
In October 1986 a crater 200 metres
in diameter, 75 metres deep formed.
It has expanded until now, when the
cavity is more than 230 by 600 metres
across. Its outward progression is still
continuing at a rate of 1 metre per
year (denoted by environmentalists to
be the “largest anthropogenic sinkhole
in the world”).
In 1978, an oil exploration well with a 2500 m Ordovician target was
abandoned because of stability problems in Triassic salt at a depth
around 650 metres. The well was abandoned without casing near
the bottom of the well. A second well was drilled in 1979 located 80
metres from the previous well. In March 1981, the lining of this well
broke because of cavity formation at around 550 metres, which is
the level of salt. In October 1986 a surface crater formed, centred on
these two wells. Dissolving salt may be salinising the crossflowing
artesian waters, leading to undocumented, but possible, degradation
of freshwater oases in the region.
Morisseau, 2000;
Wink Sink,
Texas, and
Whitten Ranch
Sink, New
Mexico
On June 3, 1980 the Wink Sink
formed a 110 m wide and 34 m deep
collapse crater. It was centred on the
Hendrick 10 A well in the Hendrick
oil field. Whitten Ranch Sinkhole or
collapse crater formed sometime
between August 31 and September
5, 1998 and was up to 23 m wide and
33m deep.
It appears likely that the natural processes of salt dissolution, cavity
growth and resultant chimney collapse atop the Permian Capitan
reef were accelerated by oil drilling and extraction activity in the immediate area of the sinkholes in the early part of last century. Large
water filled sinkholes (as in the “Bottomless Lakes” of New Mexico)
are a natural part of the landscape in the region and were collapsing
long before the arrival of man.
Baumgardner et al.,
1982
Powers, 2000
Johnson, 2001
Panning Sink,
Kansas
It formed in April 1959 with a diameter
of 90 metres and had a water surface
more than 18 metres below the
sinkhole lip.
Formed by subsidence and collapse around an already tilted and
abandoned salt-water-disposal (SWD) well - Panning 11A.
Walters, 1978, 1991
Lake Peigneur,
Jefferson
Island
Louisiana
On November 20, 1980, Lake
Peigneur disappeared in hours as it
drained into an underlying salt mine
cavern. Within hours, a collapse sinkhole 0.91 km2 in area developed in the
SE portion of the lake and in 12 hours
the underlying mine had flooded,
some 2 days later the lake had refilled
with water.
An oil well being drilled from barges and platforms in lake intersected an abandoned part of an active salt mine in the salt dome
that underlies the lake. Water from the lake and the intervening
natural collapse features entered the mine workings. Peigneur Lake
itself is a natural dissolution depression.
Autin, 2002
Thoms, 2000b
Thoms and Gehle,
1994
Sinkhole atop
Weeks Island,
storage facility,
Louisiana
An active sinkhole some 10 metres
across and 10 metres deep, first noted
near the edge of the SPR facility in
May 1992. A second, much smaller
sinkhole was noticed early February
1995, but it lay outside the area of
cavern storage.
The sinkhole led to the decision to drain the facility of its hydrocarbons. Drainage and remediation was completed in 1999 at a cost
of US $100 million. This facility was not purpose built, but was an
old salt dome mine facility. In hindsight, based on an earlier event,
one might fault the initial DOE decision to select this mine for oil
storage. A groundwater leak in the mine in 1978 may have been a
forewarning of events to come. Injection of cement grout into the
flow path controlled the leak at that time, but it could just as easily
have become uncontrollable and formed a sinkhole.
Neal and Meyers,
1995
Bauer et al., 2000
Mont Belvieu
sinkhole, Texas
July 30, 1993 a sinkhole crater formed
between two brine storage wells. The
crater stabilized in a few hours with a
diameter of 12 metres and a depth of
6 metres. It was filled with sand a few
days later.
Large volumes of brine are periodically cycled in and out of the brine
cavern in the caprock. It is used to drive the withdrawal of the stored
hydrocarbons in other deeper storage caverns. Using a system that
stores saline brine in a caprock, even without the possibility of the
collapse of a brine well, means there is a possibility of groundwater
contamination from leaked storage brines.
Cartwright et al.,
2000
Table 3. Events associated with oil wells or storage (see appendix 1 and Warren 2015 for full description of these and other sinkholes).
roof stability problems, as seen in the various roof collapses of a number of shallow salt mines in the former
Soviet Union, including a major collapse in the Solim’sk
potash mine that began in October 2014 and is still ongoing (February, 2015). Earlier mine collapses related to
unexpectedly “leaving the salt” have occurred in New
York State, Michigan and Kansas (see Table 2 and Appendix 1). Any deeper than 1100 m, and mining is taking
place at temperatures too hot for human operation of
equipment and the rates of cavity closure are too high
for conventional mining at atmospheric pressure.
Salt solution mining is the current methodology feeding
the NaCl brine plants in the Seneca Lake region. Salt
solution mining is just what it says, the mining of various salts by dissolving them and pumping the resulting
brine solution to the surface where it is concentrated
or processed to recover the desired chemical products
(Figure 4). Actual dissolution and recovery methodology
is predicated on the solubility of the targeted salt, which
in the Seneca Lake region is halite. A“rule of thumb” in
the solution mining industry is that every 7 - 8 m3 of
freshwater pumped into a cavity will dissolve 1 m3 of
halite. Water or undersaturated brine is injected through
7
Storage
cavern
Time and place
of accident
Reserve
resource
Accident
description
Accident cause
Economic loss
Number
of casualties
Influence scope
Petal City
1974, Mississippi, USA
Liquid
butane
Fire & explosion
Human error
leading to
overfilling
Homes destroyed within
7 km
24
injured
Influence range was 7
km, 3000 evacuated
West Hackberry
1978, Louisiana,
USA
Petroleum
Fire & blowout
Packer failure
during repair of
casing
72,000 bbls (about 11,446
m3) crude oil leaked, US $
14-20 million loss in total
1 fatality, 1
injured
Influenced area was
90,000 m2, environment
polluted
Mont
Belvieu
1980, Texas,
USA
Liquid
propane
Fire & explosion
Casing failurecorrosion
23 million m3 of propane
loss
At least
1 fatality
75 families (300 people)
evacuated for 180 days
Conway
1980-2002,
Kansas, USA
Liquid
propane
Gas leaking
into the groundwater
Hydrated cap
rock
Gas found in wells and
local groundwater possibly
caused by wet rockhead
None
Area near the storage
cavern, 30 homes
bought, 110 people
relocated
Mont
Belvieu
October, 1984,
Texas, USA
Liquid
propane
Fire & explosion
Casing failure
Several million US $ loss
None
Mont
Belvieu
November,
1985, Texas,
USA
Liquid
propane
Fire & explosion
Transmission
pipeline cut off
110 m3 of propane consumed and a large amount
of propane leaked
2 fatalities
Viriat
1986, France
Ethylene
Gas cloud
Ground facilities
broken
All gas leaked
None
Teutschenthal
1988, Halle,
Germany
Ethylene
Surface dome
and crack
Casing broken
60-80% of ethylene leaked
None
An area of approximately
8 km2 evacuated
Clute
1988-1989,
Texas, USA
Ethylene
Gas escaping
Drilling operation resulting in
tightness failure
About 20,000 m3 of ethylene loss
None
10 families evacuated
Brenham
1992, Texas,
USA
Liquefied
petroleum
gas(LPG)
Fire & explosion
Overfilling and
valve failure
332,000 barrels (about
52,500 m3) US$5.4 million
& US$1.38 million punitive
damages awarded
3 fatalities, 23
injured
About 3 km radius of
plant, 26 homes destroyed
Mineola
1995, Texas,
USA
Propane
Fire underground and on
the surface
Pillar cracks
Cavern cycling connected
adjacent cavities, pressure
buildup and casing leak
None
The two caverns and
region within 15 m on the
surface
Yaggy
2001, Kansas,
USA
Natural
gas
Fire & explosion
Casing bend
and damage
About 5,600,000 m3 natural gas loss. Gas surfaced
in old brine pipeheads.
US$800 million law suit
2 fatalities
Part of the town
influenced,some 250
people evacuated
Fort-Saskatchewan
2001, Saskatchewan, Canada
Ethylene
Fire lasting 8
days
Failure of pipeline connecting
two caverns
14,500 m3 ethylene loss in
None
Area near the plant
Magnolia
2003, Louisiana,
USA, near
Napoleonville
Natural
gas
Gas escaping
Casing crack
More than 1,000,000 m3
natural gas leaked
None
About 30 people evacuated from Grand Bayou
Odessa
2004, Kansas,
USA
Liquid
propane
Gas escaping
Ground facilities
broken
More than 100 t (about
90,000 kg) liquid propane
leaked
None
Clute
2004, Texas,
USA
Ethylene
Fire & explosion
Drilling operation resulting in
tightness failure
Moss Bluff
2004, Texas,
USA
Natural
gas
Fire & explosion (300m
high flame )
Brine pipe corrosion, well casing
separation
At least 36 million US $
loss in gas inventory
More than 17,000 evacuated
None
10 families evacuated
None
Influence range was 120
m, 1000 people within 5
km evacuated
Table 4. Accidents associated with oil and gas storage facilities (see appendix 1).
a purpose-designed well drilled into a salt mass to etch
out a void or cavern. The resulting “almost saturated”
brine is then extracted for processing. The technique
usually targets salts at depths greater than 400 to 500
metres (1300-1600 ft) and down to 2000 m (6500 ft)
(Warren, 2015). Any shallower and there may be cavern
roof stability problems, and any deeper than 2000 m
and salt’s propensity to flow tends to close the solution
cavern, especially at lower pressures (see appendix 1).
The advantage of solution mining over conventional salt
mining or surface evaporation pans is that product qual8
Storage
cavern
Time and place of
accident
Reserve
resource
Accident description
Accident cause
Economic loss
Influence scope
Kiel
1967, Germany
Natural gas
& hydrogen
Volume lost 12.3% after
45 days
Excessive creep of salt,
operating at too low
pressure
Cavern failure (reduced capacity)
The cavern
Eminence
1970-1972, Mississippi, USA
Natural gas
Volume lost more than
40%
Excessive creep of salt,
operating at too low
pressure
Cavern failure (reduced capacity)
The cavern
Stratton
Ridge
1990s, Texas,
USA
Natural gas
Cavern abandoned,
ground subsidence, settlement rate 40 mm/a
Excessive creep of salt
and in wet condition
Cavern failure
Ground above the
caverns
Bayou
Choctaw
1954, Louisiana,
USA
Cap rock collapsed, ≈245
m diameter lake formed
on the surface
Human error
Cavern failure
Ground above the
caverns
Clovelly
Louisiana, USA
Oil storage
Cavern in salt overhang
dissolved into cap rock
Thin cap rock, inadequate salt buffer
Cavern abandonment
The cavern
Napoleonville
Bayou Corne
2012-ongoing,
Louisiana, USA
Brine
cycling
Cap rock with large voids,
unexpected shale layers
in salt edge leading to
collapse
Cap rock failure, inadequate salt buffer
Cavern abandonment,
loss of brine storage
The cavern and
ground above
Table 5. Problems in pressurized storage caverns (see appendix 1 and Warren 2015 for full description).
ity and the extraction operation is not as subject to the
vagaries of rock strength or climate. Specific subsurface
mineralogies can be targeted by the well bore to obtain
a specific feedstock or chemical product, without the
need to get men and equipment from the surface to the
mine face. Solution mining can exploit folded and disturbed salt beds or deep-lying salt strata, situations not
easily mined using conventional techniques. The main
limitation of the solution mining method is an inherent
outcome of the requirement for a significant volume of
undersaturated water to be pumped into a salt bed and
returned to the surface for processing. There is always
a need to manage spent brine in an environmentally
aware manner.
Worldwide, diapiric salt masses tend to be the preferred
medium for solution mining and storage cavern creation,
as then any salt mass undergoing designed-dissolution
is typically large, thick and tends toward internal homogeneity (Figure 1). This makes it easier to purpose-design
in terms of both cavern shape and volume. Bedded salts
tend to be less vertically homogenous and so more subject to differential caving and roof collapse during the
life of the solution cavern. Worldwide, rather than the
brine product itself, more and more the cavern and its
use as a storage vessel is the rationale for solution mining.
in brinefields were poorly documented and controlled.
This led to many subsequent ground stability problems,
as summarized in Tables 2 through 5 and detailed in
the appendix chapter.
Indications of problems and management techniques
relevant to the Seneca Lake region will be referred to
in parts 2 and 3 of this scoping report, so it is highly
recommended that the reader refer to the details in
the chapter in Appendix 1, before proceeding with their
reading of the remainder of this report.
Reading of the various case histories underlines a very
important aspect of possible environmental problems
specific to salt extractions. This relates to the fact that
rocksalt is a highly soluble rock. Some problems are immediately apparent and can occur during the operation
of an extraction and processing facility. Other problems
may not surface until decades after the extraction operation has ceased. Once salt is exposed to an undersaturated water crossflow it will continue to dissolve over
the years and so the problem may only reach nearsurface
aquifers or the landsurface many years later.
Salt masses have been drilled and exploited as solution
brinefields for more than a century and a half. During
the late 1800s and the first half of last century, well
positions, completions and abandonment procedures
9
Part 2:
Nature of rocksalt in the Seneca Lake region
10
RondoutCobleskill
Meters
0
Bertie
Fm.
Camillus
Fm.
Feet
0
H
G
F5
60
200
F4 *
90
300
120
400
150
500
Salt
Syracuse Formation
100
SALINA GROUP
30
*
Brined along Ohio River in W. Va
*
F3 *
Mined at Cayuga, and
brined at Livonia, Watkins Glen N. Y.
*
F2 *
*
F1
*
*
Mined at Cleveland, Ohio; Detroit Michigan;
and Ojibway, Ontario
Brined at Barberton, Ohio
Mined at Fairport Harbor, Ohio and Myers, N.Y.
and brined at Rittman, Ohio and Ludlowville N. Y.
Brined at Painsville, Ohio
E
Brined at Akron, Ohio
D *
Vernon Formation
Shale
Dolomite
Anhydrite
* Thickness variation in
extracted salt layersis likely
due to combination of
deformation and dissolution
C
B *
Mined at Retsof, N. Y. and brined
at Silver Springs, N. Y.
A
Lockport
Group
Figure 5. Stratigraphy (rock unit names) used to describe salt units in New York State and surrounds, along with a listing of targeted
salt interval in former and current mining or brine well operations across the region (after Tomastik, 1997).
Salt geology
Salt in the Seneca Lake region is currently extracted in
the Watkins Glen region as a solution brine for use as a
chemical feedstock and in solid form from the nearby
Cayuga mine mostly for road de-icing (Figures 5, 13). The
salt source lies in variably dissolved and deformed beds
of the Vernon and Syracuse formations that together
make up the Salina Group. The 416-418 million-year-old
(Silurian) Salina Group extends from Michigan through
upstate New York and into the Appalachians and south
into Indiana (Figures 6, 7).
Syracuse Formation
Thickness
0
Contour interval is 250 ft
1250
N
Craton
2500
0
n
Appalachian Basin
0
elt
a
Blo
om
ay
ow kha
l
no ab
To -s
k - l flat
e
e
Cr tida
ills onW o
lag
sb
ur
gD
S
Michigan Basin
asi
lt B
a
S
n
na er
ali salt
Appalachian Basin
0
0
50
100
50 100 150
150 mi.
200 km
Figure 6. Distribution and thickness of salt in the Salina Group.
11
12
System
Middle
Upper
Llandovery
Wenlock
Ludlow
Pridoli
Lower
Middle
Upper
International
Series
S
Ohio Shale
Brassfield Member
Drowning Creek Formation
Alger Shale
Wells Creek Dolomite
High Bridge Group
Lexington Limestone
St. Peter Sandstone
Deicke Bentonite Bed
Millbrig Bentonite Bed
Drakes Formation through Clays Ferry Formation
Crab
Orchard
Group
Boyle Dolomite
Rome Trough
Tonoloway Ls.
Lockport Dolomite
Bass Islands Dolomite
Helderberg Limestone
Cincinnati group
Queenston Shale
Clinton ss/Cabot Head Sh/Medina ss
Brassfield Limestone
Cabot Head Sh.
Lower Silurian carbonates and shales, undivided
Rochester Shale
Tymochtee Ls. &
Greenfield Ls.
Salina Group
Big Mountain
Shale
Oriskany
Sandstone
Marcellus Shale
Red Shale
Limestone
Limestone with chert
Gray Shale
Black Shale
unnamed anhydritic
dolomite
Black River Group
Sandstone
unnamed sandstone
(St. Peter Sandstone
equivalent)
Deicke Bentonite Bed
Hamilton
Group
E W
Sonyea/Genesee Fms.
Tully Limestone
Mahantango Formation
Brallier Formation
Deicke Bentonite Bed
Bentonite beds
Deicke Bentonite Bed
Antes Shale
Millbrig Bentonite Bed
Juniata Fm.
Bald Eagle Fm.
Tuscarora Formation
Rose Hill Formation
Wills Creek Fm.
McKenzie Member
Beekmantown
Group
Loysburg Formation
Black River Group
Dolomite with evaporite beds
Dolomite
Wells Creek formation
Keyser Formation
Tonoloway Formation
Queenston Shale
Reedsville Shale
Trenton Group
Utica Shale
Medina Group
Lower Silurian carbonates
and shales, undivided
Rochester Shale
Lockport Dolomite
Keefer Sandstone
Salina Group
Bass Islands Dolomite
Shriver Formation and
Licking Creek Limestone
Mandata Shale
Corriganville Ls. & New Creek Ls.
Ridgeley Sandstone
Marcellus Shale
Queenston Shale
Lorraine Group
Utica Shale
After Ryder et al., 2007 (and references therein
Black River Group
Trenton Limestone
Oswego Sandstone
Medina Group
Clinton Group
Eramosa Dolomite
Salina Group
Lockport Group
Akron Dolomite
Helderberg Group
Onondaga Limestone
Oriskany Sandstone
Group
E
Rhinestreet Shale Mbr.
U. Devonian strata, undivided
Sonyea/Genesee Formations
Tully Limestone
Hamilton Moscow/Ludlowville/Skaneateles Shales
West Falls Fm.
Angola Shale Mbr.
Western and Central
New York
Venango Gp Catskill Fm.
Bradford Gp Foreknobs Fm. Perrysburg Fm.
Dunkirk Shale
Elk Gp
Scherr Fm.
Java Formation
W. & Cent. Pennsylvania
Valley &
Ridge
Marcellus Shale
Tioga Bentonite
Huntersville Chert / Onondaga Limestone Needmore
Shale
Columbus Limestone
Delaware Limestone
Bois Blanc Formation
E W
Rome
Trough
Chagrin Sh. equiv. rocks Chagrin Shale
Three Lick Bed
Dunkirk Sh.
Olentangy Shale (upper) Java Fm.
Angola Sh. Mbr.
Rhinestreet
Shale Mbr
Rhinestreet Shale Mbr.
Olentangy Shale (lower)
Huron Mbr.
Cleveland Mbr.
Bedford Sh
Eastern and Central
Ohio
Utica Shale
Utica Shale
Millbrig Bentonite Bed Trenton Limestone
Millbrig Bentonite Bed
Black River Limestone
Trenton Limestone
Juniata Formation
Reedsville Shale
Tuscarora Sandstone
Rose Hill Formation
Newburg sandstone Wills Creek Formation
McKenzie Limestone
Keefer Sandstone
Salina Group
Bass Islands Dolomite
Keyser Limestone (upper)
Mandata Shale
Helderberg Limestone
Oriskany Sandstone
Huntersville Chert
Marcellus Shale
Mahantango Formation
Tioga Bentonite
Onondaga Limestone
Hamilton
Group
Rhinestreet Shale Member
Sonyea/Genesee Formations Tully Ls.
Ohio
Shale
E W
Huron Member of Ohio Shale
Java Formation Angola Shale Mbr.
Upper Devonian Strata, undivided
Central West Virginia
West Falls Fm.
N W
Keefer (Big Six) Sandstone
Salina Group
Lockport Dolomite
Helderberg Ls.
Oriskany Sandstone
Onondaga Limestone
Clinch
Ss.
Rose
Hill
Fm.
Rome Trough
Eastern Kentucky
Valley
& Ridge
Correlation chart of Middle and Upper Ordovician, Silurian, and
Devonian rocks in Kentucky, New York, Ohio, Pennsylvania,
and West Virginia
Paleozoic
Figure 7. Stratigraphic correlation panel showing how the rock unit names vary across the region, but the evaporitic Salina Group is regionally extensive (extracted from Ryder et al., 2007).
471.8
460.9
443.7
428.2
422.9
418.7
416.0
397.5
385.3
Era
Corniferous
AGE
(Ma)
Devonian
Silurian
Ordovician
Upper
Lower
In the Michigan basin the Salina Group reaches thickness
greater than 2,500 feet (760 m) and consists dominantly
of alternating carbonate rock and salt layers (Figure 6).
Southward the Salina Group lacks salts, becomes thinner (both depositionally and erosionally), and extends
into a roughly wedge-shaped unit ranging in thickness
from 500 feet (150 m) (northeastern Indiana) to as
little as 50 feet (15 m) (central Indiana). To the east of
the thick Salina salts in the Michigan basin, the Salina
Group in the Appalachian Basin, retains salt units and
in total thickness can exceed 1250 ft (380 m) (Figures 6,
7). Depth to top of the Salina Group in the Appalachian
Basin ranges from 0 along the outcrop in New York and
western Ohio to more than 9,000 ft (2,740 m) deep in the
center of the Appalachian depositional basin. The top
of the Salina Group ranges from about 1,400 ft (430 m)
beneath the shore of Lake Erie to more than 10,000 ft
(3,050 m) below sea level in the vicinity of Muncy, LycomSouth
2000
North
1000
Genesee
0 Feet
Onondaga
Hamilton
Sonyea
Westfalls
Canadaway
Canadaway
Canadaway
Westfalls
Tully
Medina
-2000
Clinton
Salina
Lockport
Helderberg
Devonian
Sonyea
Genesee
Tully
Hamilton
Onondaga
Oriskany
Helderberg
-1000
Oriskany
-3000
Salina
Silurian
-4000
-5000
Approximate Location of
Cross Section
Beekmantown Black River
New York State
-6000
Lockport
Clinton
Medina
Trenton
Queenston
Lorraine
Queenston
Lake Ontario
-7000
Data used was
taken from
this area.
-8000
Lake
Erie
-9000
N
0
-10000
40
Scale In Miles
Potsdam
Galway
Limestone
Shale
Dolomite
Sand
Evaporites
Sand and Shale
Lorraine
Little Falls
A.
Precambrian Complex
North
Ordovician
Trenton
Black River
Beekmantown
Little Falls
Galway
Cambrian
Potsdam
South
Some fault/ disturbance zones appear to
transect the Salina Group (even at likely depths
of 2000-3000 ft) implying a brittle nature
to some salt intrabeds
Basement
Tully
Upd
like ip thin
ly re
n
late ing of
d to
Sa
salt lina g
loss roup
(dis
solu
tio
Onondaga
Salina
no
Queenston
r de
form
atio
n
)
Trenton
Black River
Beekmantown
B.
Figure 8. Beds of the Salina Group (including salt layers) dip or deepen to the south, as shown in: A) the stratigraphic cross section and
B) a regional seismic line - this line was published without a position or a scale to maintain commercial confidentiality. As the beds of
the Salina group approach the surface the total thickness of the unit lessens, likely due to the natural dissolution of the salt layers.
This implies there is a natural supply of brine to the shallow parts of the stratigraphy (base images extracted from Smith et al., 2005).
13
ing County. The Salina Group ranges in thickness from
about 300 ft (90 m) in Erie County to over 2,200 ft (670
m) in north-central Pennsylvania in Tioga and Bradford
Counties (Figure 6). Salt beds in the Salina Group can
occur in both the Syracuse and Vernon formations and
so are informally termed the Cayugan salts.
Group maintains its integrity and overall thickness. This
is likely one of the reasons why not all of the salt layers
are present in the Salina Group at shallower depths, and
one of the main reason for changes in bed thickness at
shallower levels. The other is deformation related to
regional tectonics and we will deal with this factor later.
All beds in the region of Seneca Lake show a consistent
gentle southerly dip, as seen in the stratigraphic cross
section and the north-south seismic line illustrated as
Figure 8. This section has a strong vertical exaggeration
so the beds appear to deepen steeply. This is a standard
geological presentation construct, designed to give the
viewer maximum visibility of the various rock units and
layers that make up the stratigraphy. Actual dip angles
in true scale are much less and beds would appear much
thinner in a true scale section.
Groundwater dissolution means individual layers and
overall salt thickness increase in a southerly direction.
This is why any study of suitability of the salt beds for
gas storage will show it improves to the south. Smith
et al., 2005, in a regional study of salt suitability for gas
storage in New York State, outlined the region of suitable
salt thickness and purity, mostly to the south of Seneca
Lake (Figure 9). The map is predicated on the adage of
“stay in the salt” mentioned earlier. They define rocksalt
beds as thicker than 200 feet as ideal and thicker than
100ft as feasible for gas storage. Their salt integrity
criteria, consistent with current world best practice,
are as follows:
What is interesting in the seismic line is the overall
thinning in the strata of the Salina Group as the beds
approach the surface. This is typical of dipping salt beds
worldwide and is a direct indication of the dissolution of
the salt layers as they get shallower and come into contact with crossflowing undersaturated groundwaters.
This geometry implies that the salt at shallower levels
beneath the Seneca Lake region is naturally supplying
brines to the aquifer system. At deeper levels the amount
of natural dissolution is far less and the salt in the Salina
“... The first criterion establishes salt intervals that lie at
the appropriate depth for cavern development. Depths
are selected where the geostatic pressure is sufficient
to maintain the compression-expansion systems used
to inject and withdraw (product) from the cavern, but
shallow enough to avoid cavern closure due to creep. The
suggested depths for economic cavern construction are
Salt Cavern HAMILTON
Suitability
Lake Ontario
Scale
0
OSWEGO
25
50
KILOMETERS
NIAGARA
ORLEANS
ONEIDA
WAYNE
MONROE
Well Symbols
Salina Group
Outcrop
FULTON
GENESEE
CAYUGA
Wells withHERKIMER
Raster logs
Wells without Raster logs (From Rickard, 1969)
ONONDAGA
MADISON
MONTGOMERY
Isopachs
LIVINGSTON
Lake Erie
ONTARIO
ERIE
SENECA
YATES
WYOMING
04162
Feet
CORTLAND
TOMPKINS
0
> 200
Feet
(optimal)
ALBANY
OTSEGO
SCHOHARIE
Region of salt that meets the thickness and
quality criteria, but not the depth criteria
CHENANGO
SCHUYLER
CHAUTAUQUA
CATTARAUGUS
ALLEGANY
GREENE
TIOGA
STEUBEN
DELAWARE
BROOME
CHEMUNG
ULSTER
(after Smith et al., 2005)
Figure 9. The light-brown shaded portion of this map represents that area underlain by F-unit salt that meets both geotechnical
criteria, as defined by Smith et al (2005), for salt cavern stability (provided the cavern remain in the salt) The red-dashed line and
no shade area below represents an area rejected based on their standards of salt unit purity, depth and thickness criteria. Salt in the
rejected portion (shown in white), while likely thick enough is not deep enough for cavern development, based on industry standards.
Large portions of Stueben, Chemung, Tioga, Broome, Cortland, Tompkins, Allegany and Schuyler Counties are underlain by F-unit salt
in which a stable salt cavern storage facility could potentially be created.
14
between 2000 and 6000 feet below the surface. The second and lost integrity, or roof collapse led to a loss of brine
set of criteria eliminates salt that is not of the appropriate well control, the well was plugged and abandoned and
thickness and quality for cavern construction. The salt a new solution well was drilled. Since the 1960s and
available in New York State is bedded, which dictates that 1970s, maintenance of solution brine well integrity and
caverns must be wide and short, sort of peanut shaped. minimisation of roof collapse became the aim of most
To be economic caverns are typically developed in salt brinefield operators, with the exception of operations in
that is between 100 and 300 feet thick, but thicknesses the former Soviet Union and its satellite states.
greater than 200 feet are optimal. To account for salt
In the past the practice of uncontrolled brinefield exquality, intervals of salt were
considered that were at least
Venice View Dairy Well
16120-00-00
100 feet thick and contained
GROUP
FORMATION
Depth
no nonsalt intervals thicker
600
than 10 feet. Higher quality
salt maximizes solution min700
ing efficiency and minimizes
800
the amount of rubble left at
900
the bottom of the cavern after
mining is complete....”
NEU
45
-15
DEN
GR
0
200
2
3
1000
In the past, solution cavities
created for use as a brine feedstock did not need to follow
this set of criteria. Caverns
were allowed to transect a
number of intrasalt beds,
as long as they continued to
supply a brine-stock. Once
the cavern was breached
1100
1200
MARCELLUS
ONONDAGA
1300
1400
HELDERBERG
1500
anhydrite
BERTIE
1600
CAMILLUS
1700
halite
1800
SYRACUSE
structure encased in homogenous salt (Figure 1). But such
cavities are only possible in
salt domes or thick bedded
salt, not in the thinner layers of salt with a number of
intrasalt beds that typify salt
occurrence in the Seneca
Lake region (Figures 5, 9) . It
should be noted here that salt
cavities that transect a number of salt interbeds or have
cavern roofs that breach the
salt mass are not considered
appropriate for storage under
Smith et al.’s set of criteria.
HAMILTON
F
lst./dol.
1900
2000
E
D
shale
2100
2200
2300
C
SALINA
2400
VERNON
A “peanut-shaped” cavern is
not the geotechnically ideal
vertically elongate cavern
B
2500
2600
A
2700
2800
LOCKPORT
2900
3000
Figure 10. Wireline interpretation of salt interval in Venice View Dairy well with intervals selected to demonstrate wireline determinants of mineralogy (Base log image extracted from
Smith et al., 2005)
15
pansion and consequent well abandonment has led to
later problems. Some brinefield salt cavities, once out
of the salt, became so large they stoped all the way to
the surface to become collapse dolines, with associated
loss of life and property (Table 2; Appendix 1). A problem with salt cavity-related collapse and groundwater
contamination associated with stoping caverns is that
they may not become obvious until decades after brine
extraction operations have ceased. Complete removal of
salt layers by uncontrolled brinefield operations in the
early part of last century has led to the current problems
with mud boils in Tully Valley, Onondaga County, New
York (Kappel et al., 1996).
Across New York State the buried salt layers in the
Salina Group range in purity and thickness, along with
the number of intrasalt beds. Targeted layers are ideally more than 95% pure NaCl. Regionally the salt beds
beneath New York State contain higher proportions of
impurities than their lithostratigraphic equivalents in
the Michigan Basin. Salt layers in the Michigan and Ap22902-00
County: CHEMUNG
Town: Catlin
Quad: Montour Falls
22924- 00
County: CHEMUNG
Town: Veteran
Quad: Montour Falls
77°10'0"W
3600
3700
4000
3300
42°20'0"N
4400
Horseheads
3
7
NY1
Corning
TIOGA
42°10'0"N
22899-00-00
CHEMUNG
4500
U
NY1
4300
3600
3700
Elmira
4600
3900
4000
3800
F
4
41
NY
5
S1
22924-00-00
22902-00-00
STEUBEN
4200
3500
4100
3400
42°20'0"N
42°10'0"N
CAMILLUS
3900
TOMPKINS
SCHUYLER
3900
3200
3800
3100
3000
2900
3000
3100
3200
3300
3500
3600
BERTIE
4700
NEW YORK
PENNSYLVANIA
42°0'0"N
5000
5100
each indicates 100 ft thickness
5400
Gamma Ray Curve
Non-salt Intervals
Neutron Porosity Curve
5800
5700
5600
5500
Salt Intervals
A
Stratigraphic tie-lines define top of unit or formation
6200
5400’
5900
5200
5300
5400
5400’
76°20'0"W
6000
5000
5100
5200
5300
5400
LOCKPORT
42°0'0"N
76°30'0"W
6100
4700
4800
4900
5000
A
76°40'0"W
5300
4600
4700
4800
B
76°50'0"W
5200
4500
4600
4400
D
77°0'0"W
WELL LOCATION MAP
4900
4200
4300
E
NY427
4800
4100
4200
4000
4100
NY17C
4300
4400
Ithaca
NY34
4500
42°30'0"N
9
4900
76°20'0"W
NY34B
NY8
5100
B
YATES
3700’
76°30'0"W
NY34
Watkins Glen
C
5500
76°40'0"W
42°30'0"N
NY14
Salina Group
76°50'0"W
SENECA
77°10'0"W
5400’
77°0'0"W
NY34
3400
22899-00
County: CHEMUNG
Town: Erin
Quad: Erin
NY327
ONONDAGA
ORISKANY
COEY MANS
COBLESKILL
3700
11. Wireline logs are geophysical measurements of rock
properties in a well bore. They are measured by a string
of tools lowered on a cable (or wire) and then raised to
the surface at a constant rate of rise, as measurements
of rock properties are made. The gamma log measures
natural radioactivity in the rock, values tend to be high
in shales and low in salt and carbonates (limestones
and dolomites) that lack impurities. The density log
measures electron density and converts it to equivalent
rock densities. Anhydrite has a distinctive high density
value around 3, halite is around 2, while the densities of
the other rock types varies according to porosities and
matrix constituents. The neutron log measures hydrogen content. When the neutron log and density logs are
NY414
3000’
MANLIUS
3800
Lateral and vertical extent of impurities and thickness of
salt intrabeds in the Seneca Lake region is indicated by
published examples of wireline log data, as in Figures 10,
13.2 km
10.0 km
3000’
palachian basins are separated by shales and dolomites
and variably capped by a unit with abundant anhydrite
(CaSO4), locally known as the Bertie Fm (Figure 5).
Figure 11. Salt correlation panel based on wireline log measures in three wells located south of Seneca Lake (base images extracted
from Smith et al., 2005)
16
overlain on a standardised scale, as done in Figure 9,
then regions where the two trackways overlap indicates
a likely limestone, some separation indicates dolomite,
while a broader separation of tracks indicates shale. A
reversal of the dolomite and shale overlap direction
indicates a likely sandstone. Wireline interpretation
techniques are used to better understand lithology
throughout the oil industry and is increasingly in use
by the mining industry. Its use minimises the need to
collect core, which is an expensive process.
Figure 11 is an example of the use of the wireline data
to correlate the extent of the salt and nonsalt intervals
between three wells south of Seneca Lake. It clearly shows
that the salt thickness is not consistent between wells
and that the amount and thickness of nonsalt beds varies between wells. The diagram is drawn with the intent
of maximising a bed-parallel correlation of intrasalt
units between the various wells. There is no control
on the orientation of the beds between the wells other
than an assumption that the intrasalt beds are aligned
sub-horizontally. This is standard geological practice
in the oil industry. However, regional observations as
seen in published seismic and in public-domain core
and mine-based observations (detailed next) all suggest intrabed extents and dips within the Cayugan salt
are far less predictable than such highly interpretive
correlation panels suggest.
The seismic line illustrated in Figure 12 shows the Salina
Group geometry in the vicinity of a fault zone and how
the salt body it carries can show substantial thickness
changes, especially in zones of tectonic disturbance and
deformation. This is clearly unlike the evenly-bedded
near-constant-thickness salt layers that typify salt occurrences in the Michigan Basin. The salt in the Salina
Group in its current eastern extent beneath New York
State and Pennsylvania is variably deformed, with resulting thickness changes in individual salt layers (as can
be seen locally in the Cayuga Mine; Prucha, 1968 and
discussed further in next section of this report). This deformed region includes strata beneath the Fingers Lake
region, as indicated by the shaded rectangle in Figure 6.
Tully
Onondaga
Salina
Queenston/Medina
Trenton
A.
Unintrepreted seismic line
Intrepreted seismic line
NORTH
SOUTH
Tully Limestone
Thrust fault in Tully - Cayuga
Crushed Stone Quarry
Cayuga Mine
No. 1 shaft
Hamilton Group
(includes Marcellus Shales)
Onadaga lst.
Roundout-Helderberg carbonates
Bertie dolo
mite.
Camillus Shale
Salina Group (salt)
B.
Firtree Anticline
NOT TO SCALE
Figure 12. Regional variations in salt thickness (in the Salina Group) as interpreted in A) Seismic (from Smith et al., 2005) and B) an
interpretive schematic based on regional thickness changes seen in wells and observations in the Cayuga Mine (after Goodman and
Plumeau, 2004a, b).
17
Thus, the salt beds of the Seneca Lake region and its surrounds are intensely folded into a series of local east-west
anticlines and synclines, with elevation differences of
more than tens of feet from crest to crest in local folds
in the Cayuga mine area (Jacoby, 1963). However, as the
published seismic shows, there are much greater lateral
thickness changes in the salt across faulted regions, and it
is likely that some of these faults have locally penetrated
the Salina Group (Figure 12).
steepened and thrust-faulted southeast limbs (Figure
12; Frey, 1973). This leads to the contrast in deformation
style seen in Figure 12a. Above the base of salt the beds
are folded and deformed, while below the base of salt
the beds are gently dipping. Hence, salt and incompetent
shales in the Salina Group have flowed plastically during
regional tectonic events in the Mesozoic era. This gives
rise not only to the intense folding in and above the salt
level, but also to faulting of the salt section (Figure 12a).
Regionally, as first expressed by Gwinn (1964), the various
anticlines in the Finger Lake region, and regions further
south, are the principal products of halokinetic deformation. The various salt-cored anticlines and synclines
(including the Firtree Anticline) extend downward to
the décollement (slippage) surface near the base of the
salt layers in the Salina Group. Currently a dip slightly
in excess of 1° is present at the base of the Salina Group;
this is true from the vicinity of the Finger Lakes region
to the structural front of the collision belt at the Muncy
anticline in Sullivan County, Pennsylvania. In this distance of approximately 85 miles, the base of the Salina
The upper surface of the salt and its overlying sediments
are characterized by broad, east-west synclines and anticlines, with axes generally paralleling the sharp folds
and salt-cored deformation zones in the underlying
evaporites. In contrast, beds below the décollement or
slippage layer near the base of salt are not folded. This
structural contrast, in combination with ongoing natural
Group drops from 1,000 ft below sea level near Himrod,
New York, to more than 10,000 ft below sea level west of
the Muncy anticline.
Down this incline, sliding of post-salt beds likely formed
the salt-core anticlines, with characteristically over-
salt dissolution in the shallower regions, and an earlier
episode of dissolution tied to the Alleghanian Orogeny
explains why the wedge-shaped plate of post-salt rocks
thins from about 12,000 ft thick near the structural front
to less than 2,000 ft in the Cayuga Rocksalt Mine (Frey,
1973; Harrison et al., 2004).
Inergy’s experience in the Watkins Glen area is, “...that
the gross thickness of the Salina salt beds across the field
have been faulted and folded along the décollement at
the base of the salt, as is the case throughout the New
Figure 13. Current distribution of the Cayuga Salt Mine workings beneath Lake Cayuga (image downloaded from www.arcgis.com
on Feb 5., 2015).
18
York and Pennsylvania salt basin...” (DSEIS - Appendix
-O part 11 downloaded from http://www.fingerlakeslpgstorage.com/) .
One key to the regional fault-salt cavern stability considerations is how much seismicity, tied to fault movement, and ongoing dissolution related to undersaturated
groundwater cross flows continues today as this would
be related to the formation of higher permeability
pathways from the level of the salt to the nearsurface.
Based on a regional study of fault trends and seismic
events in New York State, Jacobi (2002) concluded, “...It
thus appears that not only are there more faults than
previously suspected in NYS, but also, many of these
faults are seismically active...”
Salt observations based on present
or past mine operations
The geology of two mines are relevant to defining the
nature of Cayugan salt for this scoping study; they are
the Lansing Mine (Cargill Deicing Technology’s Cayuga
Mine) and now closed and abandoned Himrod mine,
formerly operated by Morton Salt.
Cayuga (Lansing) salt mine
The Cayuga Salt Mine in Lansing, New York, is the deepest
and oldest of two room-and-pillar salt mines currently
operating in the state of New York, the other operation
being American Salt’s mine. The Cayuga Mine processes
approximately 2 million tons of road salt, which is
shipped to more than 1,500 locations throughout the
northeast United States. The production shaft was completed in 1918 at a depth of 1,468 feet to the shallowest
salt bed. The surface plant was then completed, and
mining began in January 1922. Between 1922 and 1970,
the mine operated via conventional salt extraction from
four levels in the Syracuse Formation that encompassed
the D and F units (Figure 5; Goodman and Plumeau,
2004a, b). Today operations are focused on the D level.
Currently, the mine extends some 7 miles under Cayuga
Lake with 6 main tunnels in the mine for ventilation,
transportation and haulage (Figure 13).
Operations below Cayuga Lake create an advantageous
situation in terms of “staying in the salt” compared to
mines in areas of former brinefield operations. It is
unlikely the current Cayuga mine workings will intersect unexpected anthropogenic solution cavities or
undocumented abandoned brine wells. In other regions
of the world such intersections have led to mine floods
and consequent abandonment and closure of the mine
(Table 2; Appendix 1).
For example, the Retsof mine located some distance
to the west and formerly operating at somewhat shallower depths was lost to such a flood. It is not known
if the expanding operations of the Retsof salt mine,
which at the time was the largest salt mine in the US,
unexpectedly intersected a natural brine-filled cavity
or an anthropogenically-created solution brine cavity.
Salinisation problems in deep aquifers of the Retsof area,
resulting from this flooding and the intersection of the
mine waters with cross-flowing aquifers are ongoing in
the region around the now flooded and abandoned mine.
The geology of the Cayuga Mine was documented in
detail by Prucha (1968). He found that the salt distribution was not as flat-bedded depositional units but that
the salt layers, along with interbedded dolomites and
shales, were caught up in regional deformation ( folding and faulting) processes, which had changed the
thickness of the D and F salt units (Figure 14). Based on
work in and around the mine he found that the Firtree
Point anticline is a composite feature with second- and
third-order sized folds superimposed upon the major
structure (Figures 12a, 14a). Numerous small-scale
doubly-plunging disharmonic folds with amplitudes
up to 30 m and wave lengths up to 100 m revealed
a progressive change in mode of deformation, from
flexural-slip folding controlled by competent dolomite
beds, to passive folding controlled by the much weaker
rheological properties of the salt.
The change in deformation mode followed obliteration
of the structural integrity and competence of dolomite
interbeds, which failed on extension fractures, formed
when individual flexural-slip folds reached a critical
radius of curvature. This has created excursions from
the predicted consistent thickness of the various salt
layers and in places breaks up the continuity of the
intrasalt dolomites and shales, so that they evolve into
salt-encased breccias. The resulting varying thickness
19
A.
B.
Dolomite
10 m
Salt (halite)
Salt flow direction
0
1000
2000 ft
Lake Cayuga
Structure contour on
top of 4th salt (contour
interval is 10 ft)
1500’
1550’
1600’
Figure 14. Salt top and salt thickness vary in the Cayuga Mine (after Prucha, 1968). A) Structure contour (in feet) on top of the “4th”
salt, this is top D in the current terminology. B) Illustration of the ability of salt to flow, while adjacent interbeds do not, so illustrating
one mechanism for lateral changes in salt thickness.
of salt layers, as seen in the Cayuga Mine, is illustrated
in Figure 14b (Prucha 1968). In some places this lateral
variation in thickness is controlled by stacking of the
salt and its intrabeds into fault–thrust repeated salt
units, these are somewhat thicker than predicted by the
undeformed salt thickness (Jacoby 1969). In other places
the same salt layer was squeezed to where it is no longer
present and brecciated beds of what were once nonsalt
layers separated by salt have come into direct contact.
This style of intrasalt deformation within the thicker salt
beds means that regionally one cannot assume a laterally continuous subhorizontal layering in the intrasalt
dolomite and shale beds (e.g Figure 15). When salt beds
are targeted for solution mining this is not a problem
as the rubble from folded beds and salt breccias merely
falls to the floor of the cavern as the salt is dissolved
and cavern expands. However when a cavity is to be
utilised for pressurised gas storage the intersection of
folded and dipping intrasalt beds with both cavity and
overlying beds or faults away from the cavern edge can
become a significant factor in cavern integrity and roof
stability. It can create a subsurface situation where the
cavity has an unexpected connection to non-salt rocks
(see part 3).
Himrod Mine, Seneca Lake region
1m
Dolomite
Salt
Figure 15. Field sketch of the geology visible in a mine wall showing clearly that the distribution of non-salt beds in the rocksalt
is clearly not horizontal (after Prucha, 1968)
The Himrod mine is located to the immediate west of
Lake Seneca and was constructed in the 1960s and early
70s near the town of Himrod to supply rocksalt to the
Morton Salt Plant (Figure 16). Its geology is detailed
in this report as it offers a publicly available geology
20
Himrod mine (abandoned)
Morton Salt
stratigraphic well
Well locations in
various active and
inactive locations
Figure 16. Location of the former Himrod Mine, the Morton Salt stratigraphic well, and various brine field and hydrocarbon
wells to the south.
analog to the salt units of Watkins Glen brinefield and
the intervening area. The mine was completed and
put into operation in 1972 at a cost of $37,000,000 and
closed in 1976. Entrance to the mine was gained through
two 18-foot concrete-lined shafts equipped with Koepe
Hoists (Jacoby, 1977).
Mining was conducted in a room and pillar system, which
reportedly required the significant close-spaced bolting
of the roof. Jacoby (1977) noted many areas of the roof
were so unstable as to require bolting through mesh
and bars on much closer centers than normal for most
salt mines. After extraction of the salt was completed in
an area, large portions of the mine were then closed off
as a precautionary safety measure due to roof stability
problems. This was not a problem in the Cayuga mine
where mined-out rooms were not subject to roof collapse for periods of twenty years or more (Prucha, 1968).
According to Jacoby (1977) these unstable roof conditions in the Himrod mine were brought about primarily
due to the faulting of the Salina Group in the southern
Finger Lakes area. Mining at Himrod was conducted in
a down-dip direction to the west-southwest at depths
around 2000 ft in a unit interpreted at the time as the B
salt and so equivalent to the unit exploited in the former
Retsof Mine (Figure 5).
Although, according to Jacoby (1977), severe internal
faulting of the Salina Group beds had occurred in the
Himrod area, his mine and core observations showed
both the top and bottom of the Salina Group sequence
were relatively flat lying. With a total capacity of about
3,000,000 tons annually, the maximum production that
was achieved during the mine’s short operational life was
about 1,200,000 tons. Of the total tonnage produced,
1,000,000 tons were in nonmarketable fines termed F. C.
salt, which was particulate matter of a size smaller than
10 mesh, with a high level of insolubles. The mine was
closed in the late summer of 1976 due to high mining
costs, related to a combination of mine roof maintenance
costs and high volumes of product with unacceptably
high insoluble contents.
As part of the Himrod mine study, a series of cored
boreholes were drilled into the salt to define its nature
and extent. Chute (1972) studied the cores and stated, “...
These cores provide new information on the stratigraphy
and disclose the presence of a flat décollement in the
upper part of the Syracuse Formation (Late Silurian)...”
Chute (1972) further reported core-based evidence of
collapse of overlying beds, following irregular solution
of the salt. He argued this was the cause for some folds
in this vicinity. He suggested also that this décollement
may be the same as that reported by Prucha (1968) in
and around the Cayuga Mine. What is significant is that
Prucha’s observations on the nature of the salt come from
“within the salt” while Chute’s and Jacoby’s observations
include direct observations of the upper contact of the
salt, a situation which the ongoing mine operations at
21
Cayuga salt mine avoid (“stay in the salt”). The Himrod
cores directly sample the transition out of the salt into
the overlying rocks and so are directly relevant to interpretations of cavern roof stability.
Worldwide, coarsely crystalline halite (crystal diameters
≈ 0.5cm or more) constitutes a range of ancient rocksalt
units. Some coarsely crystalline halite preserves clear
indicators of its depositional origin (Figure 17a). Other
examples of coarsely crystalline halite have lost all indication of the original depositional texture and now preserve
evidence solely of the structurally-induced responses,
the stresses and strains that allowed the original halite
to recrystallise (Figure 17b). This deformed rocksalt
shows well-developed parallel layers, but it is structural
layering, related to flattening and smearing of salt during flow, not preserved primary depositional layering
(Figure 17b). This process of coarse layer-parallel recrystallisation typifies all rocksalt units that have flowed.
Figure 17 illustrates key differences in rocksalt textures
using what is the most recent example of depositional
textures in a thick saltern deposit from Pleistocene
rocksalt (core collected at 140 m depth) in the Dallol
Depression, Ethiopia. This
is compared to salt caught
up in a halite décollement
(thrust fault) sequence, as
exposed in the Khewra Mine,
in the Himalayan foothills of
Pakistan.
Cores from the Watkins Glen
brinefield and gas storage
region, where the nature of
the salt textures are of prime
interest to the discussions
of this scoping report, are
not publicly available. However, core photographs from
a borehole a few miles north
of the brinefields area, offer
the closest available evidence
as to the nature of the salt
(see Figure 16 for location).
The well is the Morton Salt
Stratigraphic Core Test well
(API 31-123-13174-00-00)
and reasonable quality images of the various core trays
are available online (<http://esogis.nysm.nysed.gov/
Cores_TOC.cfm>). Selected images of the various salt
units (B through D) intersected in this well are illustrated
as Figures 18 and 19.
Based on the author’s experience, all salt textures in
these core photos indicate that Cayugan salt has flowed
and deformed into a sequence of coarsely recrystallised,
structurally-aligned halite beds and layers. Likewise,
the intrasalt beds in this well show evidence of tectonic
brecciation and fracturing. That is, all the textures and
structures seen in the salt layer cores, recovered in the
Morton Salt Stratigraphic Core Test well, are structural
(Figure 18). There are no depositional layers or internal
sedimentary structures preserved. The salt and its intrabeds have clearly folded and fractured in this well.
There is no evidence for original depositional bed parallel
layering in this recovered core.
The implication is that one cannot assume subhorizontal
stratigraphic correlation lines in the Cayugan salt and
its intrabeds in this area. As in the Cayuga Salt mine,
Stressed décollement halite that
forms 100% structural layering
Coarse crystalline halite
showing upwardoriented depositional
alignment
Core from 140m depth in the
Danakil depression
Ethiopia
A.
Elongate coarse-biaxial décollement
halite in matrix of deformed potash ore
Mine wall photos from the décollement zone in the Khewra Mine,
B. Himalayan foothills, Pakistan
Figure 17. Textures in coarsely crystalline rocksalt can be used to indicate depositional versus
a structural origin. A) illustrates depositional layering. B) Indicates structural layering (depositional layering has been totally destroyed by shear and recrystallisation, with resultant elongate
(boudin-like) aligned coarse halite crystals and layers.
22
Upper contact of salt is
disturbed/brecciated
1979.6 to1998.3 feet
2010.5 to 2042.2 feet
Partially brecciated nonsalt at upper contact
Flowage layering in salt
unit (biaxial flow salt
is variably oriented)
Salt filled fractures in
underlying non-salt rock
Coarsely recrystallised
flowed salt-purer sample
Coarsely recrystallised
salt with nonsalt at base
Morton Salt Stratigraphic Core Test Well
API 31-123-13174-00-00
Figure 18. Selected core tray photographs illustrating the deformed and brecciated nature of salt in the
Himrod Mine area - Refer to Figure 16 for the position of this well and its location in relation to the actual
mine and brinefields north of Watkins Glen. Images downloaded from <http://esogis.nysm.nysed.gov/
Cores_TOC.cfm>, last accessed Feb 10,2015.
23
Impure
brecciated salt
Coarsely recrystallised
elongate salt flow prisms
(showing 2 orientations
of same crystal style)
Impure
brecciated salt
Salt-filled fractures in
underlying non-salt rock
These 3 core trays sample a portion of the much thicker salt interval that was the target level in the Himrod mine
Flowed salt
separates
breccia levels
Salt breccia with brown
non-salt clasts in salt
1690.0 to 1714.2 feet
1923.4 to 1939.0 feet
Flowed salt
separates
breccia levels
Coarsely recrystallised
and flowed salt
Morton Salt Stratigraphic Core Test Well
API 31-123-13174-00-00
Figure 18., continued. Selected core tray photographs illustrating the deformed and brecciated nature
of salt in the Himrod Mine area - Refer to Figure 16 for the position of this well and its location in relation
to the actual mine and brinefields north of Watkins Glen. Images downloaded from <http://esogis.nysm.
nysed.gov/Cores_TOC.cfm>, last accessed Feb 10,2015.
24
Morton Salt Stratigraphic Core Test Well (API 31-123-13174-00-00)
1650.4
1583.5
1631.5
Satin-spar gypsum vein fill
indicative of collapse extension
above a now dissolved salt bed
possibly related to the zone of
broken (poor recovery) core.
Salt breccia, with abundant dolomite clasts
(tectonic or dissolution rubble?)
1657
Satin-spar gypsum vein fill
and broken/
missing core zone
1596
Core recovered from a zone equivalent to what was the roof interval in the former Himrod Mine
Indicators of a former, now dissolved
slightly shallower salt level
Figure 19. Rock-core based observations relevant to the nature of the top of a salt unit and indications of former, now dissolved
salt levels in the Cayugan salt of the Salina Group. Images downloaded from <http://esogis.nysm.nysed.gov/Cores_TOC.cfm>, last
accessed Feb 10,2015.
the salt units in the Seneca Lake region must thicken
and thin. Constant bed thickness will be the exception
not the rule when modelling this salt style and internal sub-horizontallity of intrasalt beds should not be
assumed when modelling the internal layering in the
salt-dominated sections of the Salina Group.
When the Himrod mine was active, there were constant
concerns over unexpected roof falls (Jacoby, 1977) and
in 1974 a Himrod miner was killed by an unexpected
roof failure. Roof stability was an ongoing problem
when the Himrod mine was active and the Morton Salt
Stratigraphic Well core helps with an understanding
of why roof stabilization was such a problem for the
Himrod miners. Even though part of the target-ore salt
horizon, the upper portion of this salt interval is broken
and brecciated. Attaching roof bolts into this rock layer,
rather than into a unit with mechanical integrity, would
have been an ongoing problem.
The exact nature of the roof to the salt in the Himrod
area and the presence of dissolved salt layers is indicated
by textures in the recovered core. First, there is a zone
of poor core recovery (rubble in the core above the last
zone of recovered core at top salt), which is an indication
of a lack of mechanical integrity at this level in the stratigraphy (Figure 19). The last core tray below this rubble
zone shows the salt at this level is a highly-disturbed,
highly-impure salt breccia. Second, in the horizons above
the current salt layers there are there are a number of
layers indicating dissolved salt in the form of evaporite
dissolution breccias. These levels are characterised by
disturbed and rotated blocks, typically separated by
abundant veins of satin-spar gypsum (Figure 19). Satin
spar gypsum indicates extension in response to cavity
creation, formed as the salt dissolves naturally in zones
of undersaturated porewater cross flow. The dissolution
creates the void space where the satin-spar vein-fill then
precipitates. This set of classic dissolution textures is
an indication of an undersaturated hydrology and that
Cayugan salt is dissolving, with its products passing
naturally into the regional hydrology.
What needs to be confirmed is whether this process is
still active in the brinefield area and, if so, what will be
its effect on anthropogenic storage caverns with respect
to longterm roof stability. If still active, it enhances the
likelihood of stored product leakage into the cavern
surrounds, especially if a salt cavern roof is in contact
with this type of fractured lithology in the overburden
and the cavern is filled with gas under pressure.
In any undisturbed situation, salt units in contact with
undersaturated waters dissolve from the edge inward.
The salt away from its dissolving edge is largely undisturbed and maintains its inherent low permeability.
25
This is why thick salt makes such an excellent seal. The
analogy for natural salt dissolving in the subsurface is
that it dissolves in a fashion similar that of a melting
block of ice. It disappears from the edges inward, while
the interior remains undisturbed.
Forming a storage cavity in a large thick salt mass, well
away from any dissolving edge, means the cavern maintains its integrity as the salt mass internally remains
plastic and self-healing. At the same time the brittle
overburden is gently lowered across the dissolving salt
top. However, if the salt cavity comes into contact with
the brittle overburden layer, it can set up a subsurface
situation where a hollow cavity (gas or brine filled) is now
in direct contact with a brittle roof rock. In this situation
the roof rock will ultimately fail and the overburden rock
will fracture as roof blocks fall into the rising cavity. As
long as this process of roof failure continues, the cavity will rise (stope) into its overburden strata. In some
situations above brinefields these stoping cavities have
reached the land surface to form broad collapse dolines
(see Appendix 1).
Because of the 2000 foot depth of the brine cavities in
the Seneca Lake brinefield region,a scenario of cavities
reaching the surface is considered less likely. However
there is a propensity for all cavity roofs that are “out
of the salt” to ultimately stope. They may not daylight
(reach the surface) as collapse dolines, but the cavities
will still rise some distance into the overburden layers.
Wherever this occurs there is an increased possibility
of aquifer contamination due to brine/gas contact with
shallower aquifers. This “out of salt” stoping may take
place years after cavern operations have ceased.
26
Part 3:
Implications with respect to Inergy gas storage caverns
in Cayugan salt in the Seneca lake Region
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Implications
Worldwide, when a purpose-built solution cavern constructed in a thick single salt bed or in pure diapiric
salt mass is used for storage, with appropriate sonar
and subsidence monitoring, it offers a far safer facility
for gas storage than any above-ground storage facility.
Based on the preceding discussion as to the nature of
Cayugan salt, and the case histories outlined in Appendix
1, two general observations are relevant to considerations of the storage of gas in salt caverns in the Seneca
Lake region.
1) Ideally a salt cavern for pressurised gas storage should
be designed so that the cavern’s perimeter remains in
the salt (Figure 1; Gilhaus 2010; Warren 2006, 2015).
2) When facilities used to create a salt cavern are not
purpose built then there may be integrity problems in
the wells used to construct the salt and in the cavern
boundary connections. These problems may become
apparent both in the short term, measured in years, and
long term, measured in decades, (refer to Tables 2-6 and
case histories detailed in Appendix 1).
Let us now expand on these two general conclusions
with respect to salt cavern storage in the Seneca Lake
region. As a basis for this discussion we will use the
geological understanding presented in this scoping
report and apply it to the cavern outline panel made
public by Inergy (Figures 20, 22; the full scale pdf of this
A-A’ panel supplied in the Appendix 2 folder). Figure 20
illustrates Inergy’s interpretation of the position of the
Figure 20. Geological cross section with scale showing relative position of the proposed storage caverns withing the Seneca Lake
stratigraphy. The full A-A’ cross section of which this figure is a part is presented in the Appendix 2 folder.
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Cavern in1999
Cavern intersects
Unit F-1/2
Cavern in 2009
From 1999 to 2013 the surveys of cavern centred on Well 58 show it has stoped (migrated
upward) until the roof is completely out of the salt. The current situation is one that could
lead to unexpected roof failure (span size prior to collapse is dependent on roof rock strength)
Cavern in 2013
Cavern intersects units F3 an F4
Flat roof indicates “out of salt” situation
This flat span is near 200 feet across
Figure 21. History of cavern evolution centered on Well 58 (extracted from Inergy section A-A’, full document is presented in Appendix 2).
proposed storage caverns within salt in the context of
the regional geology. Figures 21, 22 and 23 show the
detail of the various cavities. Figure 20 shows that the
proposed storage caverns are developed in a variety of
Cavity elongation in what
is noted as shale implies
the geological shading in
figure is problematic, i. e.
inferred based on an
assumption of
subhorizontal orientation
of intrasalt layers and not
reality based on cavity
position.
stratigraphic levels in what is interpreted as the F salt
in the Cayugan - Salina Group stratigraphy. Figure 21
shows the upward migration of the cavern centred on
well 58 from 1999 to 2013. This upward expansion oc-
Leakage is an indication
of what happens in a
situation where the cavity
approaches or passes into
an “out of salt situation.
Note how inferred intrasalt
bed shading in shale is
modified to explain this
situation.
Figure 22. Cavity evolution centered on wells 30 and 31 along with well 45 position, the latter is a well with an unexpected pressure
connection. (the figure base was extracted from Inergy Cross Section A-A’ presented in the Appendix 2 folder)
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curred during the exploitation of this cavity as a brine
feedstock well. The most recent sonar scan in 2013 with
its characteristic flat roof shows this cavity is clearly now
in an “out of salt” situation. Any gas stored in this cavern
will be in direct contact with unsupported non-salt roof
rock. The current cavern situation is less than ideal for
cavern integrity, more so, if the cavity is expanded beyond the 2013 outline, as suggested in the Inergy cross
section. The geomechanical strength of the roof strata
must be established before this cavity is ever considered
as suitable for gas storage. This is especially so if a future
roof collapse occurs, because then the stoping “out of
salt” cavern may rise into more permeable units with
connections to deeper units. Or, if the cavity rises further,
to even shallower aquifers
Figure 22 illustrates two features of interest. First the
position of the cavity associated with well 45 is likely in
an “out of salt” situation and this likely explains the lack
of pressure integrity in this well. Second, it illustrates
the highly interpretive nature of the intrasalt geology
and inferred layering in this section. As drawn, the salt
shale not a salt unit. This is a highly unlikely situation
and illustrates the arbitrary nature of the construct used
by Inergy to illustrate any internal layering in the salt.
Also, in the vicinity of the well 48 cavern, the intrasalt
layers are drawn as a local synclinal fold to explain the
pressure connection, yet nowhere else in the A-A’ section
is the intrasalt layering drawn as folded in this fashion.
Both these examples bring into question how much is
actually known about the structural style in the salt unit
and its intrabeds in the region of proposed salt storage.
If the geological fold styles and salt thickness changes,
which are documented via mine operations (Cayuga
and Himrod mines) and in the Morton Salt Stratigraphic
Core Test well core, are also present in this region then
the inferred and assumed subhorizontal layering, as
drawn in the A-A’ cross section, are likely not the most
correct representation of the salt geology. It would be
better represented by a salt décollement layer near the
salt base and a series of folded intrasalt beds, some of
which may be in contact with the roof of the salt layer
(see Figure 1).
cavity centered on wells 30 and 30A is developed in a
The wells used to create and
maintain access to the cavern
are more than 3 decades old.
Concerns in terms of longterm
seal integrity associeted with
non-purpose design and
plugging
Inclined cavity roof and base,
along with flattened shape,
may indicate intrasalt
layering is not subhorizontal
Figure 23. Illustrates cavity evolution centered on wells 27 and 46 (out of section), along with well 28. The wells that created this
cavity were drilled some 30 - 40 year ago and the cavern is not purpose-built for gas storage (the figure base was extracted from
Inergy Cross Section A-A’ presented in the Appendix 2 folder).
30
Figure 23 illustrates the outline of cavern centred on
wells 27 and 46. The position of this cavern is within
the salt and in terms of position it is perhaps more
suitable for gas storage. However, the inclined floor of
the cavern could indicate inclined intrasalt beds that,
if part of a broader fold, offer the distinct possibility of
beds coming into contact with the overlying nonsalt
overburden strata.
Perhaps more significant in terms of cavern integrity is
the age of the access wells used to create the cavities,
which were drilled in the 1950s. This would have been
done without consideration of any future use as pressurised gas feeders. Their age and the cement technology
in use at the time to set the well casing, and the fact the
wells were passaging brine for decades and not gas under pressure, means that if this cavern is to be used for
pressurised gas storage, then longterm well integrity and
conditioning must be thoroughly assessed. This should
be done prior to their recommissioning as access wells
for pressurised gas storage.
31
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