Numerical Simulation Study on CO₂ Pre-injection in Highly Water-sensitive Tight Conglomerate Reservoirs

Abstract The Upper Urho Formation in the Mahu A well area features water - sensitive tight conglomerate reservoirs, mainly in P 3 w 2 2 , with 0.1 mD average permeability and strong water sensitivity. Early anti - swelling measures and horizontal well plus volume fracturing technology increased initial production, but couldn’t curb the steep production drop. To tackle these issues, a 280m five - spot vertical well pattern was adopted in the test area for a CO 2 pre - injection pilot test. Based on logging interpretation of 18 completed wells, a detailed geological model was built. Numerical simulation optimized CO 2 pre - injection perforation and injection parameters to guide the test plan. Simulation suggests little advantage in zonal gas injection, so it’s recommended to only perforate the middle and lower reservoirs of production wells. By October 2024, post - advanced gas injection, the test area’s central old well A0XX rose from 1.1t/d before shutdown to 16.2t/d. Production wells with only middle and lower reservoir perforation had an initial maximum output 2.5 times that of wells with full reservoir perforation. Advanced CO 2 injection has begun to boost production effectively.