A Comparison of Water Flooding and CO2-EOR Strategies for the Optimization of Oil Recovery: A Case Study of a Highly Heterogeneous Sandstone Formation

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Abstract
This study presents a comparative analysis of CO2-EOR and water flooding scenarios to optimize oil recovery in a geologically heterogeneous reservoir with a dome structure and partial aquifer support. Using production data from twelve production and three monitoring wells, a dynamic reservoir model was built and successfully history-matched with a 1% deviation from actual field data. Three main recovery methods were evaluated: water flooding, continuous CO2 injection, and water-alternating-gas (WAG) injection. Water flooding resulted in a four-fold increase from primary recovery, while continuous CO2 injection provided up to 40% additional oil recovery compared to water flooding. WAG injection further increased recovery by 20% following water flooding. The minimum miscibility pressure (MMP) was determined using a 1D slim-tube simulation to ensure effective CO2 performance. A sensitivity analysis on CO2/WAG ratios (1:1, 2:1, 3:1) revealed that continuous CO2 injection, particularly in high permeability zones, offered the most efficient recovery. An economic evaluation indicated that the optimal development strategy is 15 years of water flooding followed by 15 years of continuous CO2 injection, resulting in a net present value (NPV) of USD 1 billion. This study highlights the benefits of CO2-EOR for maximizing oil recovery and suggests further work on hybrid EOR techniques and carbon sequestration in depleted reservoirs.

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