Screening and Design Criteria for Steam Assisted Gravity Drainage (SAGD) Projects

Abstract

Abstract Certain insights into screening and design of SAGD projects, derived from in-depth analyses of three successful field projects in Canada [Tangleflags, Underground Test Facility (UTF) and Imperial Oil's Horizontal Well Pilot I (HWPI) projects] are presented. It was seen that for obtaining attractive oil rates and oil reserves, one must attempt to obtain as large a confined steam chamber, as feasible. Towards this end, one can select suitable sites by carefully scrutinizing various reservoir/geological characteristics for their impact on confinement and size of an expected steam chamber. Important design options include staggering of the injectors (horizontal and vertical) around the horizontal producers in pools with mobile heavy oil; injector to injector spacing so that adjacent steam chambers merge into each other, thereby providing a more efficient mobilization and drainage of oil; and using geo-mechanical effects to advantage, by suitably programming injection and production schedules. It was seen that for continuous net pay thicknesses of 15 m or larger, encouraging performance during SAGD could be expected. Furthermore, for in-situ oil viscosities of 35 000 mPa.s or lower, staggering of injectors around the producers becomes feasible. In this case, the "steam trap" constraint on production can be ignored during early periods of steaming for obtaining high initial oil rates. If sub-fracture injectivity of steam into the formation is limited, one can attempt an "intermittent SAGD" or a "Single Well SAGD" to maximize returns. Other similar ideas for obtaining an optimal performance are also discussed.