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.

ES-SAGD or expanding solvent steam assisted gravity drainage involves the co-injection of a hydrocarbon solvent and steam to improve recovery from the SAGD process. The hydrocarbon solvent 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 ES-SAGD pilot projects with a focus on the Nexen-OPTI ES-SAGD project at Long Lake. Additionally, a literature search was performed and the data, found in public ES-SAGD papers on steam-solvent labs and simulation studies, is summarized. Nexen is also currently involved in a lab experiment being operated by AGAT involving a comparison of the performance of different hydrocarbon solvents for assisting the SAGD process.

ES-SAGD 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. ES-SAGD will also increase reserves both per well pair and on a total oilsands basis.

Introduction

SAGD is widely used for recovering Bitumen in the Athabasca oilsands. It has shown positive results but many limitations render it problematic. Upcoming technologies are being researched to benefit the most significant production performance factors required for a successful SAGD operation.

Currently, ES-SAGD is being tested and is demonstrating promising results. ES-SAGD involves co-injecting a hydrocarbon solvent with steam. The underlying theory is for steam to condense contributing latent heat to the formation, followed by the condensation and diffusion of the liquid solvent into the bitumen. This decreases the viscosity consequently increasing the rate of production and the overall recovery more than a process driven solely by steam.

The effects on the steam oil ratio (SOR), operating pressure, production rate, and total recovery are explored through the results summarized by past pilot operations and studies. Different solvents and parameters are tested to determine a successful recipe for ES-SAGD, and the outcomes are summarized showing economic improvements and successful implementation strategies. This emerging technology appears to be a solution to numerous problems faced by SAGD. Current research into the use of solvents offers a possibility for greater success in the future.

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