Abstract:

Three experiments including CT scanning during flooding, post-flooding observation of oil-bearing thin sections under high temperature and pressure, and water flooding under high temperature and pressure by microscopic etching model, are utilized to disclose the formation mechanisms of remaining oil, their types and distribution at the end of water flooding in the marine A reservoir at the bottom of the Carboniferous system, western Tarim Basin, and strategies of enhanced oil recovery (EOR) are proposed. The results show that the remaining oil is in dispersed distribution as a whole and features patchy enrichment, due to the stripping, fingering, by-passing and capturing effects; accordingly, the remaining oil can be categorized into 6 types including pore throat filling, pore half-filling, oil film on pore walls, dispersed oil droplets, throat retention and pore corner retention. Among others, the pore half-filling type and dispersed oil droplet type in the flooded areas, account for 65.4% of the total, the highest in production potential, followed by pore throat filling type in non-swept zones, which features patchy enrichment, accounting for 21%, with lower production potential. In this regard, the surfactant or gas flooding is suggested to enhance oil recovery.

Key words: flooding experiment, formation mechanism of remaining oil, microscopic distribution of remaining oil, marine clastic reservoir, Carboniferous, Tarim Basin