Effects of Completion Design on Thermal Efficiency in SAGD

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 193357, “SAGD Circulation Phase: Thermal Efficiency Evaluation of Five Wellbore Completion Designs in Lloydminster Reservoir,” by Daniel Ayala Rivas, SPE, and Ian Gates, SPE, University of Calgary, prepared for the 2018 SPE Thermal Well Integrity and Design Symposium, Banff, Alberta, Canada, 27–29 November. The paper has not been peer reviewed. During the circulation (startup) phase of steam-assisted gravity drainage (SAGD), high-quality steam injected through the injector and producer wells heats the reservoir between the wells. The viscosity is thus lowered, making fluids mobile at approximately 50 to 100°C and creating interwell fluid communication. This paper uses a simulation model to evaluate and compare the thermal efficiency of five different completion design cases during the SAGD circulation phase in the Lloydminster formation in the Lindbergh area in Alberta, Canada. The results show that completion-design configuration affects the heat transfer and thermal efficiency of the circulation process. Introduction The SAGD process is the most commonly used thermal method of in-situ recovery for extracting heavy oil and bitumen resources in Alberta and can yield recovery factors of greater than 60%. The technique requires two parallel horizontal wells, a producer and an injector, known as a well pair. The horizontal producer well is placed approximately 3 m above the oil/water contact (OWC) or above the bottom of the reservoir, and the injector well is placed above the horizontal producer well. Most SAGD well pairs are placed 5 m apart, which corresponds to approximately 50 kPa of hydrostatic head from the injector to the producer. The lateral section of the well pair is approximately 700–1200 m in length. The SAGD thermal method usually consists of two phases, the circulation phase and the full SAGD, or production, phase. After the circulation phase, the well pair is converted to the production phase, during which steam is injected through both tubing strings of the injector well in a dual-completion design while bitumen or heavy oil and condensed steam are produced through the producer well using natural or mechanical lifting. Constant steam injection causes the steam chamber to grow and expand in the reservoir. Variations in thermal efficiency during the circulation phase result from factors such as tubing size, well trajectory, well length, completion configuration, reservoir properties, and operating parameters. To the authors’ knowledge, no published study has determined the thermal efficiency of different completion designs during the circulation phase of a SAGD well pair in a Lloydminster formation. A previous study used a discretized thermal reservoir-wellbore modeling simulator to history match field data obtained from a SAGD well pair in the Lloydminster area. Operating Strategies and Reservoir Model The complete paper discusses SAGD operating strategies and development of well and completion designs in pilot and commercial operations.

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