Most petroliferous deltas of the world, including the Niger Delta, are found in passive margin context (Holland et al., 1990; Nehring, 1991; Grauls and Baleix, 1994). The Niger Delta continues towards the Atlantic Ocean from the Nigerian shore (A regional map and structural framework of the Niger Delta in context is shown in Part 2: Section 4.1.1). Although this is a depositional system in a regional extensional belt, farther offshore the profile forms compressive structures by gravity movements (Bilotti and Shaw, 2005). Consequently, the Niger Delta is divided into three main structural domains: (1) a shore-bound extensional domain dominated by growth faults, (2) an intermediate translational domain characterized by displaced blocks, and (3) an offshore-bound compressive domain with thrusts, fault bend /propagation folds (Heiniö and Davies, 2006). The case study is located in this zone where the profile records translational and compressive structures. The link between the seabed hydrocarbon leakage indicators and tectonics in this area was previously not understood (Le Chevalier, 2002; Sultan et al., 2007). Previous works on the general parameters controlling such leakages are reviewed in this part of the report.
Deformational processes create structural traps for the accumulation of fluids and in the same vein create the fissures through which these fluids escape (Hickman et al., 1995; Smith, 1966; Hooper, 1991; Sibson, 2006). Studies have shown that in rapidly subsiding basins, if the caprock or overlying seal is relatively efficient, fluids are retained in abnormally pressured sediments (Cole et al., 2000; Bolton and Maltman, 1998; Graue, 2000; Brown, 1990). Leakage can result from several factors which include rate of sedimentation, generation of hydrocarbons, increasing pressure with burial, pore fluid pressure evolution or changing nature of porous media, and fracturing of caprock by minor/micro or major seismicity (Reed et al., 1990). On the seabed and on shallower horizons, the leakages are expressed as mud volcano, pockmarks, shallow gas seeps and/or gas hydrates (Kopf, A. J., 2002; Hovland et al, 2002). The understanding of fluid chimneys, paleochannels, BSR and submarine hydrate pingoes (Gay et al., 2004, 2006; Lightenberg, 2005; Hovland and Svensen, 2006) becomes necessary in this work.
iESog has interest in the roles of fault kinematics, dynamics of pressure cells or compartments and effectively integrated it in the various studeis and published materials available on our resources database. The various literatures published in iESog’s book series cover the fundamental concepts of fluid leakage, faulting processes and fault zone leakage in the Niger Delta, as well as deep pressure conditions and hydrocarbon trapping, retention and leakage.