Influence of crack on imbibition efficiency of low permeability reservoir in Yanchang Chang 6 formation under high temperature and high pressure condition

The Chang 6 formation in Xingzichuan oilfield is a typical ultra-low permeability reservoir with the charactors of strong diagenetic compaction, low porosity, small permeability, the development of dissolved pores and micro-fractures, large proportion of small pore throats, and strong micro heterogeneity. At present, the researches of seepage and displacement in the ultra-low permeability reservoir are not enough. Fracturing methods and high-temperature high-pressure seepage experiments are combined with constant velocity mercury injection experiments, nuclear magnetic resonance experiments, and CT scanning experiments, then the effect of fracture length and development degree on the efficiency of oil absorption and displacement are studied. The research results show that: the high-temperature high-pressure infiltration process is mainly oil-water displacement in small pores, and water enters small pores to replace oil into large pores. The infiltration efficiency with cracks is higher than the infiltration efficiency with matrix, and the longer the slit length is, the higher the infiltration efficiency is. In the initial stage of infiltration, the residual saturation decrease with the increase of permeability, the infiltration efficiency increase with the increase of permeability, and the effect is obvious. During the development process, the degree of fracture develop should increase as much as possible, the matrix permeability should increase too, and the contact area between the matrix and the fracture should also increase to improve the seepage recovery efficiency.