Effects Of Well Placement And Critical Operating Conditions On The Performance of Dual Well SAGD Well Pair In Heavy Oil Reservoir

Abstract

Abstract The technical feasibility of applying the Steam Assisted Gravity Drainage (SAGD) process to a 10–20 m thick Saskatchewan type of heavy oil reservoir with an overlying gas cap and an underlying aquifer was examined via numerical modeling. The results suggest a potential reduction on SAGD oil recovery and process efficiency in the presence of a gas cap, an aquifer, or worse, by a combination of both. The oil recovery can be reduced by up to approximately 75% depending on the reservoir setting. Oil recovery can be increased by up to 25% by offsetting the injector from the producer from their conventional SAGD well configuration, or by adopting a staggered well pattern. There is diminishing benefit and deterioration in the SAGD process efficiency when the producer drawdown is set at more than 10–20% of the injector pressure and/or when the producer fluid withdrawal rate is higher than around 150% of the CWE steam injection rate. Some of the preliminary results suggest that the SAGD process for such heavy oil reservoirs can be enhanced through steam-gas co-injection, water-alternating-steam injection, or simultaneous steam-gas- bottom water injection. Introduction The continued success of the application of the SAGD process at the Athabasca oil sands Underground Test Facility (UTF) in Alberta has lead to a gradual diversification by the Canadian oil industry to application of the SAGD technology from the oil sands environment to heavy oil reservoirs such as those found in the Province of Alberta and Saskatchewan in Canada. Recent reported advancements in a few heavy oil thermal operations had further heightened interest in applying the SAGD technology to heavy oil reservoirs under a wide spectrum of reservoir conditions. This paper examines, via numerical modeling, the technical feasibility of applying the SAGD process to a 12 API heavy oil reservoir with 10–20 m of pay in the presence of an overlying gas cap and an underlying aquifer; the anticipated production characteristics; the issues on well configuration and well placement; key operating parameters; effects induced by the gas cap, aquifer and a combination of the two; and the potential for enhancing the SAGD process in this class of heavy oil reservoirs.