The Influence of Salt Concentration in Injected Water on Low Frequency Electrical-Heating Assisted Bitumen Recovery

Abstract

Abstract Steam injection is often not a good alternative for oil recovery from shallow bitumen reservoirs; for instance, the thin cap-rock creates the danger of steam breakthrough. For deeper reservoirs the heat losses from injection well may be prohibitive. A technology that may be better suited is oil recovery aided by electrical low frequency heating of the reservoir. This technology, well known for environmental remedial applications, has been recently field-tried, yielding promising results. The process uses electrical conductivity of connate water to propagate an alternating current between electrodes, inducing the Joule heating of the reservoir. An associated problem is the appearance of hot spots around the electrodes that may be relieved by water circulation. However, the water circulation may have a significant effect on the heating process because the electrical conductivity of the circulated water depends on its salt content. In order to find out the influence of salt concentration on process efficiency we have studied the process of salt water recirculation around an electrode using numerical simulation. The physical properties and operational data for Athabasca bitumen have been collected from the literature. The model built with CMG STARS™ simulator and tested first with available analytical solutions, has been validated and the proper choice of the underlying grid and numerical tuning parameters has been verified. The process was also studied at field scale for a common pattern of electrodes and production wells. The salt turned out to penetrate into the reservoir, far beyond the major water circulation zone around the electrodes. This process increases the electrical conductivity in a large region between electrodes, which improves the heating of the reservoir. The single-electrode simulation studies using the different tools yielded similar results for a simple problem. More complex (and more realistic) field-scale simulations show that adding salt enhances finally the oil production. In practice an upper concentration limit is given by corrosion problems at the electrodes. The reservoir simulation of bitumen recovery assisted by low-frequency heating is a challenging multiphysics problem. The understanding of the influence of salt concentration on the circulated water provided by this work is an important key in process design considerations.