Optimization of engineered water injection performance in heterogeneous carbonates: a numerical study on a sector model

One of the emerging technologies for boosting oil recovery in both sandstone and carbonate reservoirs is engineered/low-salinity water injection (EWI/LSWI). In this paper, optimization of engineered water injection is investigated using three synthetic sector models representing homogeneous, heterogeneous with channeling, and heterogeneous with gravity underride reservoirs. Both oil recovery and net present value were investigated as objective functions for the study. Eighteen design parameters were selected for the study including reservoir, operational, and economic parameters. Response Surface Methodology and Designed Exploration and Controlled Evolution algorithms were implemented for sensitivity analysis and optimization studies, respectively. The study highlighted that NPV is more representative as an objective function compared to oil recovery where the three optimized models have about similar oil recovery, but different NPVs. The sensitivity analysis showed that oil price, tax rate, and initial oil saturation are the three most influential design parameters on the net present value for the three models investigated. Moreover, the findings showed that developing the gravity underride model requires more attention as being the most sensitive model with 13 influential design parameters. The optimization study highlighted that secondary EWI is recommended to achieve the best profitability out of the three models. However, a high maximum exposure is expected due to the capital and operational costs related to early EWI application. This study is one of the very few that discusses the economic aspect of EWI while incorporating the complexity of geochemical reactions and the heterogeneity of carbonates.