Experimental Study on Oil Production Characteristics of CO2 Injection from Tight Conglomerate with Different Permeability

In view of the high initial production, rapid decline and low final recovery of horizontal wells in tight m reservoir in Xinjiang oilfield, a new development method is urgently needed, combined with the minimum miscible pressure test technology, PVT technology and large aperture nuclear magnetic resonance technology, the experiments such as minimum miscible pressure between CO2 and crude oil, CO2 expansion, continuous miscible CO2 flooding with different permeability were carried out, the interaction mechanism between CO2 and crude oil, oil production law and oil recovery characteristics of CO2 miscible flooding were obtained. The experimental results show that the minimum miscible pressure of CO2 and crude oil is 26.2 mpa and the ground-miscible pressure difference is 17.81 mpa (compared with the minimum miscible pressure measured by the thin-tube method), respectively, under the condition of reservoir, the volume coefficient of crude oil increased by 128%, the expansion coefficient increased by 83.0%, and the viscosity reduction rate of crude oil is 31.01%, remarkable solubility, swelling ability and viscosity reduction effect are one of the core mechanisms of subsequent CO2-EOR in this reservoir. The greater the core-scale tight conglomerate permeability is, the higher the CO2 miscible displacement efficiency is. CO2 miscible flooding can completely utilize the crude oil in the large pores (relaxation time is more than 100 ms) of the tight conglomerate core, and can largely utilize the crude oil in the middle pores (relaxation time is between 1 ms and 100 ms), oil in small pores (relaxation time less than 1 ms) can be effectively utilized. The higher the permeability is, the higher the proportion of oil in pores is, and the smaller the proportion of oil in pores is. It provides the technical support for the program of gas injection to improve final recovery in tight conglomerate reservoir of Xinjiang oilfield.