AN INTERVIEW WITH THE PRESIDENT OF
SAVANNAH’S FTG SURVEY PARTNER, ARKEX
Jim White
President
Can you tell us about ARKeX’s FTG technology: how it works and
where it can be useful?
The Full Tensor Gravity Gradiometer (FTG) is used for hydrocarbon and mineral
exploration and can be deployed on a marine or airborne platform. FTG surveys
measure minute variations in the Earth’s gravitational field to help image subsurface
structures. From these surveys, a detailed interpretation of the subsurface geology
can focus future exploration with the aim of reducing overall time and cost.
There are two main differences between FTG and conventional airborne gravimeters.
Firstly, the FTG is many times more sensitive, measuring a broadband gravity
signal. Secondly, it also measures the gravity gradient field in all directions. These
attributes allow us to reveal much more geological detail and map the geometry
of sub-surface features with unsurpassed accuracy. The images opposite show
conventional airborne gravity (left image), and FTG (right image) over the same
survey area. In this example, the limited resolution of conventional gravity could not
distinguish between the individual target structures whereas the FTG data could.
FTG can work well in any geological environment where lateral density changes
exist. For example, these density changes could be caused by variations in rock
type, basement topography and the presence of faults and structures.
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Is FTG a suitable technology for the Agadem basin
in Niger?
Yes. FTG has had notable and numerous successes as
an exploration technology in the East African Rift System
(EARS) and we believe it can be equally applied to the
Agadem Rift Basin which is part of the Central African Rift
System (CARS). The Agadem basin juxtaposes fault blocks
of different density associated with lithological and structural
variations producing a gravity response measurable by FTG.
ARKeX also acquired magnetic data as part of this survey
and that technique provides a useful dataset that can assist
with mapping volcanics and basement.
As a UK, new entrant company, how
straightforward was it for ARKeX to operate
in Niger?
Despite this being our first operation in Niger and the
Sahara Desert it was relatively straightforward. To get the
survey underway, ARKeX and Savannah had to make permit,
aircraft and equipment import applications with the relevant
government departments. We thank them for facilitating this
process. In tandem with this we jointly built a camp for the
crew adjacent to CNPC’s operational hub in Agadem which
includes an airstrip. The cooperation of CNPC to utilise their
airstrip was essential to the operation and we are thankful to
them for that.
The final results and interpretations are still being
prepared, but can you comment on your initial
findings and how the survey is anticipated to help
Savannah?
The preliminary interpretation is encouraging so far. Already
we are seeing potentially important structural trends, fault
patterns and suggestions of where the basement is deeper.
One of the benefits of having a continuous FTG and magnetic
dataset across the entire area is that we are able to map
these geological features in areas not covered by seismic
data.
It is important to integrate the FTG data with the available
seismic and well data too. In spring 2015 we started a phase
of 2D modelling utilising the FTG and magnetic data. This
process allows us to test different seismic interpretations
and swiftly narrow down the possible geological scenarios.
This will be followed by more detailed 3D modelling prior to
completion of the final structural interpretation. The overall
integrated interpretation process should allow Savannah to
high-grade prospective areas and redefine leads.
Example comparison of conventional gravity vs. FTG data
Individual target structures
Conventional airborne gravity
Full Tensor Gravity
N.B. Images for illustration only
Annual Report & Accounts 2014
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