| Continental slope gravity flow channel is an important part of deep-water source-sink system, and it is also a
critical target of international deep-water oil and gas exploration. The recent exploration of oil and gas has revealed that
the distribution of gravity flow channels is complex in thrust fault zone of continental slope. While the influences of thrust
faults on gravity flow channels have been studied all over the world, few researches have been carried out in terms of
microtopography styles formed under the comprehensive action of thrust-transfer structures and their control on gravity
flow channels. Taking a deep-water study area in West Africa continental slope as an example, this paper applies core,
logging and seismic data comprehensively to clarify the types and genesis of thrust-transfer microtopography and the
control of microtopography on distribution of gravity flow channels.
High-resolution 3D seismic data was employed to investigate the thrust faults and distribution of gravity flow
channel. Thrust fault traces were tracked in seismic profiles based on reflection terminations and offsets. Two stratigraphic
units (S1, S2) were interpreted according to the characteristics of seismic facies and the geometric relationship between
strata and stratigraphic surface. Both S1 and S2 were interpreted to represent the growth strata that was active
synchronously with the thrust faults. Application of RMS amplitude attribute within time windows was done for clearer
images to envisage the location and form of gravity flow channels. Paleogeomorphology maps were made from
stratigraphic thickness and indicated the distribution of gravity flow channels in the study area. Results and conclusions
were as follows: In Miocene, topography of the study area was dominated by arcuate thrust faults and fault-related folds
oriented perpendicular to the continental slope, and the thrust faults were connected by transfer structures. Thrust faults,
which were formed as a result of the gravity sliding, were developed toward the deep water. Two different thrust fault
systems in study area were developed along two detachment surfaces at different depths in the overpressure mudstone,
resulting in different thrust displacements, which was the main reason for the difference in structural style and activity
intensity between the two thrust fault systems. Displacements of two thrust fault systems and difference of the
displacement along the strike of a single thrust fault led to a variety of transfer structures. Controlled by thrust-transfer
structures, five different microtopography styles were summarized from the perspective of genesis: triangular faulted
anticline, tear fault-diapir anticline, reverse fault connection valley, tear fault slope and strike trough. Under the influence
of thrust-transfer microtopography, contemporaneous gravity flow channels showed three plane distribution styles:
diversion, crossing and confinement. Triangular faulted anticline and tear-diapir anticline deflected gravity flow channels
that were developed along continental slope. Reverse fault connection valley and the edge of tear fault slope enabled
gravity flow channels to cross the faults. Strike trough confined gravity flow channels. This study could provide a new
analytical approach for seismic interpretation of gravity flow channel reservoir. |
