Performance Evaluation of Immiscible Water Alternating Gas Injection Using Integrated Asset Modelling

Abstract

Integrated evaluation of enhanced oil recovery (EOR) performance in offshore reservoirs requires consideration of surface constraints that can limit well deliverability and field production. Immiscible water alternating gas (IWAG) injection is often assessed using standalone reservoir simulation, which does not explicitly represent interactions among the reservoir, wells, and surface facilities. This study applies an integrated asset modelling (IAM) framework to evaluate IWAG performance under operational constraints and compare it with a reservoir-only simulation. A three-dimensional reservoir model was simulated using both approaches under identical subsurface conditions. The unconstrained reservoir-only case forecast approximately 19% higher cumulative oil over the 30-year evaluation period than the IAM case. Within IAM, sensitivity analyses were performed on injection rate and cycle duration. W2G3 with an 18-month cycle was the best-performing configuration among those tested, producing 162.18 MMSTB of cumulative oil, increasing recovery factor from 13.0% to 16.0%, and adding 34.53 MMSTB of incremental oil. The results show that production forecasts are sensitive to whether well and surface constraints are represented explicitly. For the conditions evaluated, IAM provides a more representative basis for IWAG screening and pilot planning than a reservoir-only model.