Abstract:

 The qualitative and quantitative characterization of the microscopic pore structure of the reservoir can benefit the efficient development of the reservoir in the later stage. In this study, the microscopic pore structure of Chang 4+5 ultra-low permeable reservoir was characterized in  Baibao area of Wuqi oilfield by using blue-dye thin section， SEM， high pressure mercury penetration. A local pore structure classification standard of the study area was established. Based on the experimental results, a real sandstone model is built up to evaluate the quality of the pore structure by the oil-water two-phase seepage experiment, and the existence types and causes of the micro residual oil in different pore structures are analyzed through the microscopic visualization of the oil-water displacement experiment. The results show that the combination type of class Ⅰ pore structure is intergranular pore-dissolved pore, oil and water two-phase seepage characteristics are the best, after water flooding, the micro residual oil mainly exists in the form of small contiguous clusters, oil displacement efficiency is 35%; Type Ⅱ pore structure is dissolved pore-residual intergranular pore, oil-water two-phase seepage characteristics is similar to class Ⅰ, water storage capacity and water flooding effect are the best, oil displacement efficiency is 43%, after water flooding, the micro-residual oil mainly exists in cluster and ring form; Class Ⅲ pore structure combination type is intercrystalline pore-dissolved pore, it has the worst physical properties, oil and water have the worst seepage characteristics, oil displacement efficiency is only 21%, after water flooding, the micro residual oil exists in the form of contiguous clusters. The diagenesis and the pore filling content in the study area mainly affect the pore structure development, thus affecting the microscopic residual oil distribution of different pore structures after water flooding.

Key words: ultra-low permeable reservoir')">

ultra-low permeable reservoir, micro pore structure, oil and water seepage characteristics, micro residual oil