Experimental Study on Micro Production Law of Gas Drive in Mahu II Conglomerate Reservoir

The Mahu II conglomerate reservoir is commonly developed using the depletion method after horizontal well volume fracturing, which has the characteristics of rapid decline in formation energy and production. Gas drive is an effective means of energy replenishment, but the micro utilization rules and residual oil distribution of gas drive are not well understood. In order to study the micro utilization law of gas drive in conglomerate reservoirs, experiments were conducted on long core gas drive to characterize the relationship between recovery degree, gas oil ratio, and PV number. Microfluidic gas drive experiments quantified the distribution of different types of residual oil, and micro gas drive numerical simulations clarified the micro utilization mechanism of CO2 drive. The results showed that the recovery rates of long core CO2 mixed phase drive at injection rates of 0.05 and 0.1 mL/min were 57.68% and 61.44%, respectively. The recovery rates of non mixed phase drive with CO2 and CH4 at the same injection rate were 45.14% and 41.38%, respectively. Both CO2 and CH4 were utilized for micro pores, and the recovery rate was mainly contributed by pore throats with a radius less than 0.5 μ m, with a lower limit of 12nm for pore throat utilization; From the perspective of microfluidic oil displacement efficiency, CO2 miscible flooding > CO2 immiscible flooding > CH4 immiscible flooding. In Class II reservoirs, more intragranular dissolved pores are developed, and there are more cluster shaped residual oils after gas flooding, followed by corner shaped residual oils, column shaped residual oils, and film shaped residual oils; Numerical simulations of micro displacement in porous media show that CO2 miscible displacement has an efficiency about 7% higher than non miscible displacement. The displacement effect of CO2 on free crude oil is better than the stripping effect on adsorbed crude oil on particle surfaces, with the former being about 11% to 13% higher than the latter. Combining long core physical modeling experiments, microfluidic physical modeling experiments, and gas drive numerical simulations to comprehensively characterize the micro mobilization laws of gas drive can provide a mechanistic understanding for the formulation of gas injection development plans and parameter optimization in Mahu oil drive.