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The Role of Fault Kinematics and Capture in the Western Niger Delta and the Control of Sediment and Reservoir Distribution*
By
Jacob Diedjomahor1; Charles Kluth2, Eric Frost3, and Robert Mellors3
Search and Discovery Article #40092 (2003)
*Adapted from “extended abstract” for presentation at the AAPG Annual Meeting, Houston, Texas, March 10-13, 2002.
1Chevron, San Ramon, CA
2Chevron, San Ramon, CA; present address: Littleton, CO ([email protected]; [email protected])
3San Diego State University, San Diego, CA ([email protected])
General Statement
Large, south-dipping cuspate normal faults separate structural trends within the shelf of the western Niger Delta (Figures 1 and 2). The growth and linkage of these faults exerts control on the distribution, thickness and quality of reservoirs. We have examined 3D seismic, well, and biostratigraphic data to examine the structural control over reservoirs in detail in order to understand the relationship between the structure and reservoirs so that we could explore and develop fields more efficiently. The major faults link together to form trends through the process of fault capture. These faults form a linked system whose temporal pattern of movement is documented in the sedimentary record. Four-way structural traps occur in the hanging walls of the major faults.
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Structural Control on Sediment and Reservoir DistributionA chronostratigraphic framework was established by interpreting and mapping time correlative sequences and their associated sediments. A strong structural control is observed on sediment and reservoir deposition and distribution (Figures 3 and 4). There is an overall thickening of each sequence basinwards from one structural trend to the next (Figure 4). There is also a decrease in reservoir rock thickness and net-to-gross ratio from one structure-building fault towards the next younger one (Figure 5). Structural control on sedimentation is also observed within each trend in an along-strike direction, with decreasing net-to-gross ratio in reservoir rock thickness towards fault tips. The timing of displacement and linkage through fault capture is clearly shown in the thickness and reservoir facies patterns. |
Figure
1. Map of Africa showing Nigeria and the position of the Niger Delta and
the study area.
Figure
2. A 3-D view of the major structural trends in the study area.
Figure
3. Transverse profile A-A’ through the study area. (a) Interpreted time
seismic section. (b) Depth section showing faults, gamma-ray well logs
and sequence boundaries.
Figure
4. Longitudinal profile X-X’ through the study area. (a) Interpreted
time seismic section. (b) Depth section showing faults, gamma-ray well
logs and sequence boundaries.
Figure
5. Dip profile through the Meren Trend showing reservoir distribution
away from the major structure-building fault.