Developing SAGD Operating Strategy using a Coupled Wellbore Thermal Reservoir Simulator

Abstract

Abstract The MacKay River Project is located approximately 60 kilometers northwest of Fort McMurray, Alberta, Canada. The development consists of 25 well pairs and facilities to produce 30,000 bopd of bitumen from the McMurray Formation of the Athabasca Oil Sands Deposit over a 25 year life. An in-situ recovery process referred to as Steam Assisted Gravity Drainage (SAGD) is used. The SAGD process utilizes horizontal well pairs, drilled 5m vertically apart, to provide continuous steam injection into the upper well with continuous fluid production from the lower well. The initial phase of the MacKay River Project consists of two production pads that supply steam to the injection wells and accept return fluids from the production wells. Produced fluids are processed at the MacKay River central facility where the bitumen is shipped to market via an insulated pipeline. Solution gas is recovered for use in steam generation, while the water is treated and recycled. During the start-up at MacKay River, communication was initiated between each producer and injector by circulating steam in both of the wells. Once the reservoir between the two wells was sufficiently heated and bitumen mobility was evident, a pressure differential was applied between the wells for a short time after which the well pair was converted to SAGD mode. In SAGD mode the upper and lower wells be-came dedicated injection and production wells, respectively. In developing the start-up operating parameters for the MacKay River well pairs, a pseudo-compositional thermal reservoir simulator was used to perform sensitivities to deter-mine the optimum operating strategy. The reservoir properties in the model were imported from a geostatistical model that was developed for the area. A discretized wellbore using the as-drilled trajectory was also implemented in the model. This allowed for the implicit modeling of the pressure and heat transfer dynamics in the wellbore, which are very significant in a SAGD operation. The main objective when developing this strategy was how to initiate communication between the producer and the injector in the optimal time without causing adverse affects on the long term SAGD performance. The variables that were investigated during the operating strategy development included steam circulation rate, steam circulation pressure, the magnitude and timing of pressure differential implementation between the injector and producer and the optimum timing of SAGD conversion. This start-up operating strategy was successfully im-plemented in the field from September to November 2002. Subsequently, the models are being calibrated to the field measured start-up data. Upon completion, these coupled wellbore reservoir models will be used to define the optimal ramp-up operating strategy for the MacKay River SAGD well pairs. This paper will detail the sensitivities conducted and the start-up prediction that were generated through the coupled wellbore reservoir simulator with a comparison to actual field data.