Geomechanical characterization of a clastic reservoir in parts of Niger Delta, Nigeria

In this study, a Clastic reservoir in the Y oil field located in parts of the Niger Delta was characterized geomechanically using suits of well log to estimate and evaluate its geomechanical properties. The study aims to use the estimated properties to infer the rock strength and probable mechanical failure mechanism using the cross-plot method. The estimated average value of these properties is 5.4135GPa, 1.534GPa, 6.053GPa, 0.3478, 0.653GPa−1 and 27.457GPa for Young's modulus, Shear modulus, Bulk modulus, Poisson's ratio, compressibility, and unconfined compressive strength respectively. The result of the cross plots of these evaluated properties colour-coded with porosity for the reservoir 2 intervals distinguished three lithofacies: hydrocarbon sands, brine sands, and shale with varying sensitivities in the reservoir interval. The cross plots of Poisson's ratio versus elastic moduli and UCS show that the porous hydrocarbon sands exhibit high Poisson's ratio, low elastic moduli, and low UCS, while brine sands and shale exhibit moderate Poisson's ratio and medium to high elastic moduli and UCS respectively. These suggest that the hydrocarbon sands are brittle and are said to be more prone to lateral deformation being less stiff, rigid, and having less strength than the other lithologies. At the same time, shale is ductile the stiffest, and the most rigid rock in the reservoir. These observations are indications that the hydrocarbon sands are friable and unconsolidated compared to the consolidated brine sands and shale. Thus, the low strength hydrocarbon sands are prone to mechanical failures and are likely to deform easily under the influence of overburden in the reservoir interval during production.