Microcosmic mechanisms of water-oil displacement in conglomerate reservoirs in Karamay Oilfield, NW China

Targeting the conglomerate reservoir of the Lower Karamay Formation in the Middle District No.6 of Karamay Oilfield, based on the research of conglomerate reservoir characteristics and flow mechanism, laboratory experiments were conducted to study the pore production characteristics during water-oil displacement and imbibition and analyze the effect of pore structure on oil displacement efficiency, the microcosmic distribution of remaining oil and the influence of long term water flooding on reservoir pore structure. The results show that the remaining oil saturation is high, while the remaining oil is mainly in small sized pores. During the water-oil displacement, the preferential producing pores are super large pores; large and middle pores make great contributions to recovery. During the imbibition, the preferential producing pores are small pores and imbibition effect largely depends on middle and small pores. The oil displacement efficiency and microcosmic remaining oil distribution are mainly affected by pore structure. After water flooding over a long period of time, the interstitial materials expand, decentralize, move, and get eroded; large pores and throats increase; the connectivity becomes better; and the micro-heterogeneity gets more serious.