Authors: Ejokpa Godspower Irikefe, Ikechi Igwe, Emenike N. Wami
Abstract: This research investigates the effects of fluid saturation on the geo-mechanical properties of consolidated and unconsolidated sandstone reservoirs under confined stress conditions. Sandstone formations are critical for hydrocarbon production, but their mechanical behavior is strongly influenced by lithology and pore-fluid interactions. A comparative knowledge gap exists regarding how consolidated and unconsolidated sandstones respond under identical multiphase saturation and stress conditions. This study addresses the gap by experimentally analyzing six core samples obtained from the Niger Delta region of Nigeria. The cores were oven-dried, saturated with water and oil-water mixtures, and subjected to triaxial compression tests at confining pressures of 100 psi and 300 psi. Results revealed marked lithological differences: the consolidated dry core exhibited a Young’s modulus of 22,300 psi, yield strength of 34,800 psi, and peak strength of 36,775 psi, failing suddenly in a brittle manner. In contrast, the unconsolidated dry core showed a much lower Young’s modulus of 65 psi, yield strength of 2,700 psi, and peak strength of 2,915 psi, with gradual strain-softening failure. Saturation kinetics further demonstrated that unconsolidated cores achieved equilibrium within ~1 hour, whereas consolidated cores required 3-5 hours. Fluid type also influenced behavior: under water saturation, consolidated samples weakened to a peak strength of 23,497 psi, while oil-water saturation improved performance, reaching 29,350 psi. The study advances understanding of lithology-dependent saturation kinetics, multiphase fluid effects, and failure mechanisms under confinement. In conclusion, lithology and saturation state jointly control sandstone geomechanics, with consolidated samples showing higher strength but brittle failure, while unconsolidated samples exhibit lower strength with ductile deformation. This study contributes critical experimental data for refining reservoir geomechanical models and supporting sustainable petroleum production.
DOI: https://doi.org/10.5281/zenodo.23489151
