Characteristics and influencing factors of spontaneous imbibition in deep tight conglomerate reservoirs in the Mahu Sag

Abstract

Research on spontaneous imbibition in deep tight conglomerate reservoirs of the Mahu Sag is vital for enhancing oil recovery and optimizing development. This study employs porosity-permeability tests, CT scanning, contact angle measurements, volumetric imbibition experiments, and NMR T₂ spectrum/imaging to investigate impacts of core properties, size, temperature-pressure conditions, and contact modes. Findings reveal strong heterogeneity in porosity (5.4%-15.8%) and permeability (0.11–8.99 mD), poor porosity-permeability correlation, and weak connectivity with low coordination numbers (≤ 5 predominant); macroscopic connected porosity strongly correlates with permeability (r = 0.92). Reservoirs show strong hydrophilicity: interstitial clays < 10° contact angle, detrital grains averaging 30°. Imbibition recovery factors range 29.6%-50.9%, influenced by higher porosity/permeability and shorter cores. Reservoir conditions (95 °C, 56 MPa) increase recovery by ~ 8%, with temperature reducing oil viscosity for faster rates and pressure enhancing drive for longer duration. Microscopically, imbibition favors sub-micropores/micropores (up to 50% recovery), while macropores exhibit counter-imbibition and oil redistribution. Results provide insights into imbibition mechanisms, refine experimental methods, guide shut-in timing, and support efficient reservoir development.