Dissolution of Rock During Smart Water Injection in Heavy Oil Carbonate Reservoirs by Natural Generation of Acidic Water

Abstract

Smart waters have been studied for enhanced oil recovery in carbonate reservoirs, gaining significant attention from research groups and oil industry companies. However, there is a general consensus that the complexity of the fluids/rock system governs their effects, much fundamental knowledge is lacking, and many questions and uncertainties remain. For instance, the existence of rock dissolution in carbonate rocks, as a mechanism for oil production, has previously been documented. This work specifically focused on the interaction oil–brine–rock and its effect on rock dissolution. Carbonate rocks (limestones and dolomites), brines, and heavy crude oils were individually analyzed and then systematically mixed with each other to gain a comprehensive understanding of their interactions. Five heavy crude oils with different properties were tested under similar reservoir conditions (≈92 °C). Results revealed the generation of acidic water derived from the interaction between injected fluids and crude oils. Not all crude oils could produce acidic water, which is the cause of rock dissolution. This research suggests that the chemical interaction between crude oil and injected water may be one of the main reasons for the increased efficiency in response to the use of the smart waters for the improvement of oil production. Basic analyses that are presented here essentially provide an insight into the impact of the chemical interaction between crude oil and injection water with the rock. Finally, coreflood experiments were performed using a dolomitic core in order to monitor and verify the presence of dissolution during the flow of fluids. A basic crude oil was selected for this purpose. Effluent analysis, pH measurements, and permeability evaluations corroborated the influence caused by smart water injection as acidic water in contact with the rock. The findings of these experiments prove that is possible to predict and control the occurrence of the dissolution, observing interactions of crude oil and injection water.