Mahdi Kazempour

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

Injection of alkaline solutions in reservoir leads to mineral dissolution and precipitation, possibly resulting in changes in permeability and porosity, and consequently altering solution pH. Accurate prediction of pH, alkali consumption and aqueous chemistry changes are required to design suitable chemical blends in alkaline-polymer (AP) or alkaline-surfactant-polymer (ASP) flooding. Excessive consumption of alkali can result in degradation of flood performance and lower than expected oil recovery. We report state-of-the-art geochemical simulation results for sandstone reservoir mineral assemblages and alkali solutions (NaOH, Na2CO3, and NaBO2) employed in AP and ASP formulations. Single-phase high-pH corefloods were completed using Berea sandstone and reservoir samples to calibrate and validate geochemical simulations. Results show that rock-fluid interactions depend strongly on mineral type and amount, alkaline solution injection flowrate, and composition of the injected and formation water. Anhydrite, a commonly found calcium sulfate, significantly impacts pH buffering capacity, water chemistry and permeability damage against conventional alkali agents in chemical flooding particularly for 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 is present. The end consequence of this is insufficient alkalinity for reactions with the oil phase and the likely formation damage.

Crude Oil-in-water Emulsion Flooding for EOR

Injection of oil-in-water emulsions has been identified as an effective oil recovery method. McAuliffe (1973) introduced emulsion injection as a mean to increase sweep efficiency. McAuliffe compared dilute emulsion flooding to water flooding to show that injection of emulsion into sandstone cores improved sweep efficiency. In this study, alaboratory investigation is performed to characterize crude oil-in-water emulsion and to evaluate the emulsion injection to improve oil recovery. The experiments consist of injecting crude oil-in-water emulsion with known droplet size distribution through Berea cores with different permeability values to explore the effect of drop to pore throat size ratio on the effectiveness of emulsion flooding. Results show that crude oil-in-water emulsion can effectively increase oil recovery. The blockage phenomena caused by emulsion injection can be effective even when emulsion is chased by waterflooding, but the response is a function of capillary number.