Enhanced Steam-assisted Gravity Drainage: A New Horizontal Well Recovery Process For Peace River, Canada

Abstract A new horizontal well recovery process, developed for application in the Peace River tar sands of Alberta, Canada, has shown sufficient technical and economic potential to warrant a field test which commenced operations in November 1993. The new process is an enhanced version of the steam assisted gravity drainage(1,2) (SAGD) process which is currently being field tested by Alberta Oil Sands Technology and Research Authority (AOSTRA) together with a consortium of industry members at the Underground Test Facility (UTF) located in northern Alberta(3–5). The SAGD well configuration, which consists of two parallel and superposed horizontal wells, with continuous steam injection occurring in the upper well and liquid and gas production from the lower well, is also utilized in the Enhanced Steam Assisted Gravity Drainage (ESAGD) process. A performance enhancement to the SAGD process is obtained through the application of a small pressure differential between adjacent pattern steam chambers. The gentle "steam drive," which occurs once sufficient bitumen mobility has been obtained between steam chambers, is observed to be tolerant of reservoir heterogeneities. Additional benefits include accelerated steam zone growth and bitumen production, up to 50% improvement in ultimate recovery efficiency, and no impairment to the thermal efficiency relative to the SAGO process. The surface access 'ESAGD field test currently underway in Peace River is described. The Peace River oil sands are 10caEed in northwestern Alberta (Figure I). Following the oil sand deposit discovery in 1949, Shell Canada began testing a variety of in situ recovery processes, including steam soak tests in 1962. steam drive and in situ combustion testing in 1965–66, followed by steam injectivity and productivity tests in 1973–74(6,7). A 31-well pilot (Peace River In Situ Pilot - PRlSP; see Figure 2) began operations in 1979, testing the pressure cycle steam drive process(7–9). Pilot operations ended in 1992 at a cumulative recovery efficiency of 65% and cumulative oil steam ratio of 0.25. In 1986, Shell Canada commenced operations in [he Peace River Expansion Project (PREP). the only commercial project in [he Peace River oil sands, with a target production of 1,600 m3/day of bitumen from 163 producers(10). The need to improve production economics by reducing production costs was the motivation behind the Peace River horizontal well study, which began in early 1991. The use of horizontal wells in a pattern steam drive was shown via numerical simulation to result in poor recovery and thermal efficiency due 10 poor steam conformance. This led to the numerical simulation study of SAGD (1,2). SAGD without any performance enhancements did not appear to yield the desired performance uplift in Peace River. Further study ultimately led to the development of the ESAGD process. Geological Description The Peace River oil sand deposit covers an area of approximately 6,200 square kilometres and contains some 12 billion cubic metres of bitumen. The productive horizon is found in the Bullhead member of the Cretaceous Bluesky/Gething zone at an average depth of 600 m, and is geologically equivalent to the shallower. productive McMurray sands in Northeastern Alberta(11).