Reducing Steam Oil Ratio in Steam-Assisted Gravity Drainage

Abstract
North America’s long-term energy future depends heavily upon the Athabasca oilsands. Only 15% of these deposits are at mineable depths (<90m) and thus 85% of the oilsands (232 billion bbl recoverable reserves) must be recovered using in-situ techniques. Steam-assisted gravity drainage (SAGD) has become the method of choice for oilsand producers and it is therefore critical to optimize this process. Steam additives can improve recovery from the SAGD process. The additive, hydrocarbon or not, is soluble in bitumen at reservoir conditions and serves to decrease its viscosity, thereby increasing the production rate over a process driven solely by steam.

This paper investigates several steam additive pilot projects with a focus on a project at Long Lake. Also, this paper discusses laboratory experiments involving a comparison of the performance of different hydrocarbon and non-hydrocarbon additives for assisting the SAGD process. Steam additives should be pursued because successful implementation would significantly improve profitability by accelerating production, decreasing water losses and decreasing steam requirements. Additionally this will address environmental concerns by decreasing CO2 emissions associated with steam generation using natural gas. If successful, these steam additives will also increase reserves both per well pair and on a total oilsands basis.

Introduction
Steam-assisted gravity drainage (SAGD), cyclic steam stimulation (CSS), and steam floods are widely employed in the upstream industry to extract heavy oil (Boberg, 1987; Butler, 1991; Butler, 1982). These techniques utilize steam to lower the viscosity of bitumen, which translates into improved production. Sustainability of the enhanced production is primarily dependent on the ability to generate large volumes of steam. Steam generation consumes large amounts of natural gas and leads to higher CO2 emissions, which impacts profitability of the SAGD operation and the environment in a negative way. This problem, a technological void, calls for a solution with higher oil production for the same level of steam consumption, and thus higher profit margins.

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