Abstract—Subsurface rocks’ response to stress and the attendant deformation is a function of the geomechanical properties under in situ pore pressure conditions. Understanding rock behavior in vertical and lateral successions, the effects of stress on the rock sequences which often cause compartmentalization and defining fluid communication within the basin is necessary for optimizing drilling, completion and production. Rock cores are seldom available for laboratory test hence use of dynamic method. The mechanical properties and local deformation in a depth interval of 1500m and 4500m have been using wireline logs. Results shows that the mechanical property evolution was influenced by rock mineralogy, porosity, depth of burial, pore pressure, effective stress, tectonics and temperature. Increase depth of burial and effective vertical stress favoured syndepositional compaction and paleotectonic stresses greater the rock strength induced tensile fracturing and faulting culminating in kinematic translation and creation of a depositional centre in the middle of the field. Rapid progradation of sandstones and shales sequences due to marine incursion created both stratigraphic and structural compartmentalization. This accompanied by low rate of fluids diffusion and imposition of overburden load on the pore fluids, vertical transfer along the faults, grain sliding in shear; reduction in the rock compressibility and pore volume; and destruction of cement bonding causing compaction disequilibrium and generating excess pore pressure in the shales. Re - orientation of the tectonic stresses led to elastic stretching of the ductile and high elasticity shales and microfracturing of the brittle sandstones forming growth faults and rollover anticlines that favoured hydrocarbon migration from the lower Akata source rock into the porous reservoirs and shale capping and smearing on the fault limbs providing the trapping mechanism.

Index Terms—Petrophysical logs, mechanical properties, rock deformation, growth fault, roll over anticlines

Cite:Fidelis A. Abija, "Geomechanical Property Evolution and the Mechanics of Growth Faulting in a Niger Delta Oilfield, Nigeria," International Journal of Geology and Earth Science, Vol. 5, No. 2, pp. 73-95, June 2019. doi: 10.18178/ijges.5.2.73-95