Comparative scenario analysis for improved oil recovery in a heterogeneous carbonate reservoir

Efficient development of heterogeneous carbonate reservoirs is challenged by complex pore systems, permeability anisotropy, and limited pressure support. This study presents an integrated reservoir modeling approach to optimize Improved Oil Recovery (IOR) development strategies for the Cenomanian-Turonian Mishrif Formation in the Ratawi Oilfield, southern Iraq. A high-resolution static and dynamic model (2.86 million cells) was constructed using well-log, core, and production data and calibrated through history matching. Multiple simulation scenarios were designed to evaluate key parameters, including injection pattern, well spacing, well trajectory, stimulation, artificial lift, and water-cut management. Results show that natural depletion yields low recovery (4.5%), while water injection improves performance but remains limited by inefficient sweep. The integration of gas lift significantly enhances pressure maintenance and production sustainability. The five-spot injection pattern outperforms linear injection, nearly doubling recovery efficiency, while reducing well spacing from 2000 m to 1500 m improves reservoir drainage and recovery. Deviated wells show superior performance compared to vertical wells due to increased reservoir contact, and full-field stimulation (skin = - 3) increases recovery from 8.5 to 9% to 12-12.5%. Additionally, implementing a water-cut-based shut-in strategy reduces water production and slightly improves recovery (from 14.7% to 14.9%). The optimized development scenario combines five-spot injection, 1500 m well spacing, deviated wells, gas lift, and water-cut control. This strategy achieves the highest recovery factor of 14.6% after 30 years. The results provide quantitative guidance for optimizing development strategies in heterogeneous carbonate reservoirs.