Evaluation and Optimization of Hybrid EOR for Low Salinity Applications in Carbonate Reservoirs

Abstract

Significant incremental oil can be additionally recovered by applying enhanced oil recovery (EOR) process on the cost-efficient low salinity waterflood (LSWF) in carbonate reservoirs. Based on the understanding of various LSWF mechanisms, this study proposes a novel concept of carbonated low salinity waterflood (CLSWF) and polymer-assisted carbonated low salinity waterflood (PCLSWF). While LSWF is an emerging EOR method based on modification of wettability and intrinsic permeability, carbonated waterflood and polymer flood are proven methods for favorable mobility ratio. To incorporating complex mechanisms in the low salinity-based hybrid EOR, a comprehensive ion exchange model has been constructed to associate with geochemical processes, polymer degradations, and interphase CO2 transport. Laboratory core flood simulations of different LSWF schemes are conducted to understand the dissolution of carbonate minerals, ion exchange, and wettability alteration. After history matching the experimental data, numerical simulations of hybrid EOR processes were run in core-scaled and pilot-scaled formations. Overall performances of the hybrid EOR processes are investigated in terms of oil recovery and CO2 storage efficiency. Hybrid EOR methods are shown to promote the synergy of the underlying mechanisms including wettability modification, miscibility, and increased brine viscosity and overcomes problems frequently encountered in the conventional LSWF. In different pilot-scaled formations, injection strategies of PCLSWF and CLSWF are optimized by identifying key important factors such as injection rate, CO2 concentration, and polymer concentration. In addition, the oil recovery and CO2 storage capacity of NPV-optimum designs are investigated. In cooperating these finding, the proposed low salinity-based hybrid EOR process is demonstrated a promising potential in oil recovery and CO2 storage.