Steaming Uphill: Using J-Wells for CSS at Peace River

Abstract Shell Canada has tested several well designs at its Peace River in-situ operation, including vertical wells, horizontal wells, SAGD horizontal well pairs and multi-lateral wells. These well designs have been used with recovery processes such as PCSD (pressure cycle steam drive), steam drive, SAGD and CSS (cyclic steam stimulation). CSS has given the most economic oil-steam ratios of these recovery processes. A recent improvement in CSS well design has been to drill laterals from the base to the top of the reservoir at angles above 90 degrees. This "J-well" design acts as a vertical separator that helps distribute steam to the end of the wellbore, prevents steam condensate from inhibiting injection, heats the low permeability Estuarine sands at the top of the reservoir and should retain gas and steam better in the reservoir during the production cycle. The initial performance of the first J-wells at Peace River has been encouraging with higher oil-steam ratios than regular CSS wells and more effective heat distribution observed on time-lapse seismic. Introduction The Peace River heavy oilfield is located in northern Alberta, Canada. Shell's leases in the area contain around 1.1 billion m3 (7 billion barrels) of 7.5 degree API oil in a Bluesky/Gething Lower Cretaceous sandstone reservoir. The dead-oil viscosity at reservoir temperature is around 100,000 centipoise. The Peace River field was discovered by well Shell Cadotte number 1 in 1951. Pilot-scale production from the Peace River field began in 1979 with the Peace River In-Situ Project (PRISP), followed by the Peace River Expansion Project (PREP) in 1985. PRISP and PREP applied the Shell-patented Pressure Cycle Steam Drive (PCSD) recovery method, which makes use of a thin basal water zone to obtain adequate steam injectivity in vertical wells. PRISP was quite successful, with a 40% recovery and a cumulative oil-steam ratio (OSR) of around 0.3. However, PREP performance was affected by inter-cluster interference, resulting in a sub-economic OSR of less than 0.2. In 1992 Shell was an early adopter of Steam Assisted Gravity Drainage (SAGD) technology with the drilling of two 1000 m long well-pairs. This was followed by ten more SAGD well-pairs in 1996 and 1997. However, SAGD also proved to be ineffective at Peace River with a cumulative OSR of less than 0.2. The poor performance of SAGD at Peace River is attributed to limited vertical development of the SAGD steam chamber, caused by the permeability contrast between the higher permeability Fluvial zone at the base of the reservoir and the lower permeability Estuarine zone at the top. In 1996 Shell began testing Cyclic Steam Stimulation (CSS) with multi-lateral horizontal wells. CSS is a more robustrecovery process than SAGD and the high injection pressures, together with extended laterals drilled in the reservoir, enabled good steam injection rates without the need for injecting in the basal water zone. The performance of the CSS wells has been good, with typical early cycle OSRs of more than 0.4, which issufficient to provide the basis for expanded commercial development of the field.

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