Geochemical Modeling and Experimental Evaluation of High-Ph Floods: Impact of Water-Rock Interactions in Sandstone

Abstract

Abstract Alkaline flooding, either for enhancing heavy oil recovery, or in alkaline-polymer (AP) and alkaline-surfactant-polymer (ASP) flooding for lighter oils, represents an important EOR strategy. Injection of alkaline solutions leads to mineral dissolution and precipitation with likely resulting changes in permeability and porosity of reservoirs, which in turn alter solution pH. Accurate prediction of pH, alkali consumption and aqueous chemistry changes are required to design suitable chemical flooding blends. Excessive consumption of alkali can result in degradation of flood performance and lower than expected oil recovery. We report results of state-of-the-art geochemical simulations for sandstone reservoir mineral assemblages and alkali solutions (NaOH, Na2CO3, and NaBO2) employed in AP and ASP formulations. The strategy has been tested for conditions of the State of Wyoming in Minnelusa reservoir and Berea sandstones. Single-phase high-pH floods were completed in the lab to calibrate and validate geochemical simulations. Results show that rock-fluid interactions are a strong function of mineral type and amount, alkaline solution injection flowrate, and composition of injected and formation water. It is found that anhydrite has a significant impact on pH buffering capacity, water chemistry changes and permeability damage against conventional alkali agents in chemical flooding particularly in the case of Na2CO3, but no significant pH buffering is observed during NaBO2 flooding. Experimental data and model results show that the pH-buffering effect is maintained even after several pore volumes of alkaline solution are injected, if a sufficient fraction of relevant minerals are present. Comparison between linear core and field flooding simulations show that short reaction times tend to minimize these effects and may lead to conclusions that cannot be readily transferred to field cases. By applying reaction-transport modeling, the design of chemical flooding can be improved and formulation effectiveness losses caused by reservoir mineralogy can be avoided, even in cases where traditional laboratory screening procedures would indicate a suitable formulation for chemical flooding.