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Structural Diagenesis in an Upper Carboniferous Tight Gas Sandstones Reservoir Analog*
P. Wuestefeld1, C. Hilgers1, and B. Koehrer2
Search and Discovery Article #41491 (2014)**
Posted November 17, 2014
*Adapted from oral presentation given at AAPG International Conference & Exhibition, Istanbul, Turkey, September 14-17, 2014
**Datapages © 2014 Serial rights given by author. For all other rights contact author directly.
1
Reservoir Petrology, EMR I Energy & Mineral Resources Group, RWTH Aachen University, Aachen, Germany ([email protected])
2
Geology/Exploration Germany, Wintershall Holding GmbH, Barnstorf, Germany
Abstract
The effective exploration of unconventional hydrocarbon reservoirs such as tight gas sandstones is getting more important as
conventional hydrocarbon reservoirs are becoming increasingly scarce. Gas from tight gas reservoirs has been successfully
produced in the Lower Saxony Basin, Germany, for more than four decades but only contributes with a minor amount to the
overall gas production. Unconventional reserves however are vast and could significantly support the supply with domestic gas
in Central Europe over the next decades, if reservoir quality predictions as well as production technologies can be improved. We
integrate quantitative data from a reservoir outcrop analogue and contribute to the understanding of the effect of structural
diagenesis, which in turn may contribute to an enhancement of recovery factors of tight gas sandstone reservoirs in the region.
We demonstrated that the Piesberg quarry near Osnabrueck, northwest Germany acts as a suitable reservoir outcrop analogue to
Upper Carboniferous tight gas fields of the Lower Saxony Basin in terms of size, facies, structural inventory and diagenesis.
This study focuses on the multi-scale reservoir heterogeneity exposed in the Piesberg quarry, comprising fluvial sandstone
cycles of Pennsylvanian age. The main porosity is secondary and resulted mostly from carbonate leaching and limited
dissolution of feldspar. Porosity variations are both stratigraphically and structurally controlled. Primary pore space was
occluded by the development of a pseudomatrix resulting in low porosities (<10%) and very low permeabilities (<0.01 mD).
Lateral and vertical variations of reservoir properties within depositional facies and stratigraphic cycles are well documented in
high-resolution wall panels displaying porosity and permeability distributions. Structurally controlled matrix porosities increase
up to five orders of magnitude (up to 25%) in fault corridors. Fractures and fault planes are quartz-cemented around faults,
indicating localized mass transport and may be associated with the structural and diagenetic evolution of the Upper
Carboniferous of the Piesberg area. Within this R&D project, a predictive model for the carbonate cement distribution and
related porosity-permeability variations in Upper Carboniferous sandstones will be established. Reservoir quality is structurally
and stratigraphically controlled, which might lead to new well placements close to faults. This may change future tight gas
exploration.
Reference Cited
Adriasola Muñoz, Y., R. Littke, and M.R. Brix, 2007, Fluid systems and basin evolution of the western Lower Saxony Basin,
Germany: Geofluids, v. 7, p. 335-355.
Structural diagenesis in an Upper
Carboniferous Tight Gas Sandstone
Reservoir Analog
AAPG ICE 2014
Unconventional Resources: Tight Sand Plays
P. Wuestefeld*, C. Hilgers*, B. Koehrer**
* Reservoir-Petrology, EMR I Energy & Mineral Resources Group, RWTH Aachen University, Aachen, Germany
** Geology/Exploration Germany, Wintershall Holding GmbH, Barnstorf, Germany
© Energy- & Mineral Resources Group
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Location outcrop analog vs. wells
 Piesberg outcrop analog: surface, Westphalian C/D (Pennsylvanian)
 Düste tight gas field: ~ 4 km depth, Westphalian C - Stephanian
(Pennsylvanian)
 Rehden tight gas field: ~ 2 km depth, Westphalian C/D
(Pennsylvanian)
B
North Sea
HH
E Netherlands
High
Pompeckj swell HB
Lower Saxony B.
Münsterland swell Harz
DO
50 km
after Adriasola Muñoz 2007
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The Piesberg as reservoir analog
 Similar stratigraphy
 Similar fault strikes
 Similar scale
 Large “seismic-scale”
faults
 Unique, large & deep
quarry
 Size that 2 wells would
fit in one quarry
Coal seams
Large normal faults
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200 m
Take the outcrop home
 Terrestrial Laser scanning
 Geo-referenced 3D model  high resolution reservoir model
W
500 m
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Fracture network analysis
 NW of quarry, lowermost stratigraphic position
 Color-coded main fracture orientations
N
NE-SW profile
(manually measured)
Fracture orientations
from digital model
NW–SE profile
(manually measured)
N
N
N
1b
1a
3b
W
E
W
W
2
4
3a
S
© Energy- & Mineral Resources Group
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W
E
W
E
5
S
S
Fracture network analysis
 NW of quarry, lowermost stratigraphic position
 Color-coded main fracture orientations
N
NE-SW profile
(manually measured)
Fracture orientations
from digital model
NW–SE profile
(manually measured)
N
N
N
1b
1a
3b
W
E
W
W
2
4
3a
S
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W
E
W
E
5
S
S
Gamma Ray assisted lithology log
 Piesberg exposes 4 fourth-order fluvial fining-upward cycles
 Correlation & facies interpretation
Dreibänke
a
m
s
Johannisstein
Westphalian D
Mittel
s
e
Bänkchen
Kohlebänkchen
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Westphalian C
c
200 m
o
a
l
Zweibänke
140 m
4th order
GR Sed. Log cycles
Johanisstein
Gamma Ray assisted lithology log
 Piesberg exposes 4 fourth-order fluvial fining-upward cycles
s
m
a
s
e
Bänkchen
Kohlebänkchen
© Energy- & Mineral Resources Group
Institute of Reservoir-Petrology
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Westphalian C
c
200 m
o
a
l
Zweibänke
140 m
Dreibänke
Johannisstein
Westphalian D
Mittel
GR
Porosity
Sed. Log
[%]
Facies
interpretation
Lateral FloodAccretion plain
4th order
GR Sed. Log cycles
Johanisstein
Floodplain
Downstream Accretion
& Mire
 Correlation & facies interpretation
Gamma Ray assisted lithology log
 Piesberg exposes 4 fourth-order fluvial fining-upward cycles
0
2
4
6
8 10%
GR Sed. Log
i
Dreibänke
140 m
s
i
t
Johannisstein
Westphalian D
e
Mittel
PHI = 2.9%
r
o
Bänkchen
PHI = 4.9%
200 m
Kohlebänkchen
PHI = 6.8%
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Westphalian C
P
o
Zweibänke
Porosity
Sed. Log
[%]
Facies
interpretation
Lateral FloodAccretion plain
GR
s
Johanisstein
Floodplain
Downstream Accretion
& Mire
 Correlation & facies interpretation
Lateral 2D porosity profile
 Average He-plug porosity: ~ 6%, no significant lateral
5,0%
5,0% 5,7% 5,7% 6,0%
5,6% 6,2%
4,5%
4,5% 5,4% 6,7% 5,4% 5,3% 5,2% 8,1% 5,0% 6,0% 6,5% 8,0% 7,0% 8,7% 4,6% 5,9%
Westphalian D
2m
variations on meter scale within a single fluvial sandbody
W
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Westphalian C
56 m
2D profile
Structurally controlled matrix porosity
 Enhanced matrix porosity in 4 fault zones
Westphalian D
Lateral profile 2
20%
Porosity
15%
10%
Lateral profile 2
Lateral profile 1
5%
0%
0
10
20
30
40
50
60
70
80
90
100
Lateral distance [m]
Lateral profile 1
Westphalian C
Porosity
30%
20%
10%
0%
0
10
20
30
40
Lateral distance [m]
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50
60
70
80
2D profile
Diagenesis and Porosity
 Early primary porosity loss
during eodiagenesis
F<
Development of a pseudomatrix
Chemical compaction + authigenic quartz
100
0,25µm
mm
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5000,25
µm mm
Diagenesis and Porosity
 Secondary porosity evolution
during telodiagenesis
F>
Carbonate (Ankerite) dissolution
Rhomboidal pores, carbonate dissolution
3 µm
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100 µm
Diagenesis and Porosity
 Dissolution of detrital components
 Clay mineral replacement
 HC charging early Cretaceaous
Fsp  Kln  Ill
Illite mesh  Bitumen impregnation  late QZ cementation
50 µm
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50 µm
Conclusions
 Outcrop reservoir analog for N-German tight gas fields identified
 3D architecture of sedimentary bodies
 3D heterogeneity of rocks & porosities
 Extraction of main fracture sets from digital outcrop model
 3D digital fracture network
 Porosity changes with respect to stratigraphic position (base of 4th –
order cycles) and distance to faults
 Stratigraphically controlled porosity variations
 Structurally controlled porosity variations
 Paragenetic sequence established to understand complex diagenesis
and to compare with well data
 Primary porosity destroyed
 Secondary porosity due to carbonate dissolution
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Outlook
 2D wall panels for variogram analysis displaying the lateral reservoir
quality variations
 High resolution subseismic to seismic 3D reservoir model
 Fracture network modeling based on LIDAR data
 Documentation of field-scale 3D reservoir heterogeneities
 Regional correlation with subsurface data (Düste & Rehden fields) to
establish exploration-strategy with respect to tectonic setting
© Energy- & Mineral Resources Group
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Acknowledgements
 Wintershall
 Peter Suess
 Steffen Liermann
 Norbert Schleifer
 RWTH Aachen University
Institute of Reservoir-Petrology at
Aachen University of Technology
www.emr.rwth-aachen.de
 Ulrike Hilse
 Pieter Bertier
 Helge Stanjek
 Reinhard Fink
© Energy- & Mineral Resources Group
Institute of Reservoir-Petrology
www.emr.rwth-aachen.de