SEISMIC ANALYSIS OF LINKED GEOLOGICAL PROCESSES IN THE TRANSITIONAL DOMAIN OF GRAVITY DETACHMENT SYSTEMS: DEEPWATER WESTERN NIGER DELTA

Abstract

Two and three-dimensional seismic data are used to investigate some stratigraphic relationships between sedimentation, deformation and fluid flow at the lateral margin of a gravity detachment system. Three themes were studied. In the Niger Delta, a right-lateral strike-slip fault with a displacement of around 7 km occurs across 75 km. It is interpreted as the lateral strike-slip domain, linked to the updip extensional domain and the downdip compression zone of a gravity detachment system. Structural and kinematic evidence, such as present-day propagating strike-slip faults, for possible future lateral expansions of the lateral strike-slip domain, is described. We expect to observe similar domains at the margins of other preserved
gravitational collapse sliding over a detachment whose efficiency in causing downdip slip may vary laterally.
Using 3D data from both Mauritania and Nigeria, the interactions between tear faults and deepwater channels are studied. Structural observations combined with channel
analysis are performed in four case studies, illustrating that tear faults influence channel development throughout their evolution. Some examples across tear fault zones are presented, and it is expected to find such interactions elsewhere in the world.
A simple model of development of vertical fluid flow pipes is established using two examples that are 400 - 600 m wide and ~ 2000 - 2500 m high. Both examples are located at the crest of rollover anticlines and rooted in buried channel-complexes tilted during fold growth. At the crest of the structures and within the connected permeable reservoir intervals of the channel complexes, lateral pressure transfer caused the pore pressure to reach critical levels, leading to hydraulic fracturing of the overburden.
Although hydrocarbons may migrate upwards through the consequent chimney systems, the pipes are not necessarily indicators of hydrocarbon charge of the channel complexes.