A sensitivity study on modified salinity waterflooding and its hybrid processes
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Waterflood is one of the most widely used techniques in enhanced oil recovery. In 1990s researchers came to conclusion that the chemistry of the injected water can be important in improving oil recovery. The low salinity water injection (LoSal® ) has become one of the promising topics in the oil industry. It is believed that the main mechanism for incremental oil recovery in low salinity flooding is wettability alteration. Several papers discussed that the wettability alteration from oil-wet to mixed- or water-wet takes place due to clay swelling and expanding of double layer in sandstones and calcite dissolution along with rock surface reactions in carbonates. However, there is no consensus on a single main mechanism for the low salinity effect on oil recovery. The main objective of this research is to conduct sensitivity analysis on main parameters in low salinity waterflooding and its hybrid processes affecting oil recovery in carbonates. We compare results by using coupled reservoir simulator UTCOMP-IPhreeqc. UTCOMP is the compositional reservoir simulator developed at the Center for Petroleum and Geosystems Engineering in The University of Texas at Austin. IPhreeqc is the module-based version of the PHREEQC geochemical package, a state-of-the-art geochemical package developed by the United States Geological Survey (USGS). We investigate the effect of low salinity water and carbon dioxide on oil recovery from carbonates by modeling the processes through the UTCOMP-IPhreeqc simulator. We perform sensitivity analysis on continuous gas injection (CGI), water-alternating-gas (WAG) flooding, and polymer-water-alternate-water (PWAG) flooding. We study the significance of reservoir parameters, such as reservoir heterogeneity (Dykstra-Parsons coefficient, Vdp, and crossflow, kv/kh), the salinity of injected water, the composition of gas, and polymer concentration in polymer-water solution on cumulative oil recovery. Moreover, we study the importance of inclusion of the hydrocarbon CO2 impact on the aqueous-rock geochemistry by comparing two scenarios where in one scenario the hydrocarbon CO2 effect is included in UTCOMP-IPhreeqc whereas in the other one the effect is neglected. Finally, we perform sensitivity analysis on PWAG flooding for most influential design parameters using Design of Expert software. The reservoir parameters, such as average reservoir permeability, reservoir heterogeneity, and crossflow and injected polymer-water solution parameters, such as polymer concentration and salinity of injected water are optimization parameters in this study.