The wet electric heating (WEH) process (US patent 6,631,761) and its potential applications to SAGD/VAPEX initialization have been tested and validated in lab scale experiments and in field scale numerical simulations. Unlike conventional steam circulation methods, which typically heat the wells and then transfer the heat into the reservoir between production and injection wells through thermal conduction, WEH heats the reservoir directly via Ohmic heating. Since it relies mainly on electric conductivity of reservoir, the delivery of thermal energy by WEH is instantaneous. Furthermore, injection of brine into the wells provides for larger effective electrode cross sectional area, so that a larger portion of the Ohmic heating energy is more evenly distributed between wells, making WEH a more efficient initialization method. The experimental tests and numerical simulation using CMG's STARS confirmed these arguments. To investigate the economic impacts, two types of reservoirs were examined: Athabasca and Cold Lake/Lloydminster heavy oils. For a realistic range of heavy oil, bitumen and natural gas prices the analysis predicted an economic advantage, ranging from trivial to very significant, for using WEH as a SAGD initialization technique. Further, this analysis showed that economic performance depended primarily on reservoir characteristics and vertical spacing between the wells. Potential application of the WEH method to VAPEX start-up is also recognized.
Traditional and common practice for starting-up a SAGD operation is to circulate steam in both production and injection wells and thus transfer heat by thermal conduction to heat up reservoirs between the well pair. The end of the initialization period is marked by the achievement of fluids communication between the two wells [1]. This process could take a long time, from a couple of months to half a year for a typical average well spacing of 5 meters. Reducing the time required for the initialization period could have profound impact on the economic value of a SAGD operation. The shorter the starting- up period is, the shorter the payback period and the higher the net present value (NPV) is. Inexpensive solvents have been tried in the field to accelerate the start-up process, but the improvement was limited. Applying a small pressure gradient between the two wells may result in acceleration of the initialization period. However, it is known that such process is fundamentally unstable, and therefore, extra cautious steps must be taken when exercise this process. Up to date, it is still not clear whether such practices have resulted in the heating distribution reasonably even longitudinally along the wellbore direction. In attempting to significantly and effectively accelerate the SAGD initialization process, Alberta Research Council has recently developed an alternative procedure, the Wet Electric Heating (WEH) technology [2], that uses low frequency AC electrical power to heat the reservoir between the injection and production wells during the start-up period.
In past decades, numerous attempts have been made to use electric heating for oil recovery. However, due to lack of technical and economic advantages, further advances in field applications of electric heating have not been significantly made.
