The Effect of Operating Pressure on the Growth of the Steam Chamber Detected at the Hangingstone SAGD Project

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Abstract At the Hangingstone reservoir of the Athabasca oil sands, Japan Canada Oil Sands (JACOS) started initial steam circulation of the SAGD Phase I project in April 1999, and the regular operation in July. The expected performance was achieved in the early period. The operation pressures were gradually raised from 4,800 kPa in mid-November 1999 to 5,300 kPa in mid- December. In early 2000, initial circulation of the Phase II wells, which consist of three SAGD pairs of 750 m wells, were started. Steam produced at the Phase I steam generator was supplied to warm up these wells. Because of this dual use of steam, the injection pressure of the Phase I wells had to be reduced to 4,600 kPa. A significant change in the growth rate of the steam chamber was detected at some of the observation wells. This was reflected as a suspension of vertical growth of the steam chamber. A new generator to supply steam for Phase II wells was completed in July 2000. Accordingly, the steam injection pressures for Phase I wells were increased in August and the vertical growth of the steam chamber was resumed. The measured temperature changes in the observation wells, the results of numerical simulation study, and conceivable mechanism of the growth of steam chamber are presented in the paper. Introduction The Steam Assisted Gravity Drainage (SAGD) process has been widely accepted as an in situ recovery process of bitumen from oil sands reservoirs. There are many pilot and commercial scale projects currently underway in Alberta(1). Japan Canada Oil Sands Ltd. (JACOS) has participated in the Underground Test Facility (UTF) project since 1992 and has endeavored to develop a clear understanding of the process. The original recovery mechanism presented by Butler(2) has been improved by introducing more realistic convective heat flow(3–5) and accumulation of noncondensable gas(6) in the reservoir. The major effort, however, made during the last ten years was a field study using a numerical simulator. Special emphasis was placed on understanding the growth mechanism of the steam chamber by rigorous simulation of temperature changes at observation wells. Most of the temperature changes measured at observation wells and horizontal production wells for many SAGD projects, including Imperial Oil's vertical-horizontal well project(7), UTF Phases A, B, and D, and Hangingstone Phases I and II, have been reproduced by numerical simulation. A part of the above study involving the UTF Phase B and early Hangingstone Phase I projects(8) was presented in 2000. A phenomenon of "generation of an impermeable layer during the AGD process" was developed during the subsequent examination of the previous article(8), which is presented in this paper. Hangingstone SAGD A-Pair The Hangingstone Phase I SAGD project consists of two pairs (A-pair and B-pair) of 500 m horizontal wells. Initial circulation was conducted from April 14 to July 27, 1999, followed by a regular SAGD operation. The early performance was close to our expectation(8) and the steam chamber was detected in many observation wells.