Interpretation of Temperature Observations From a Cyclic-Steam/ In-Situ-Combustion Project
- Ben I. Nzekwu (BP Resources Canada Ltd.) | Richard J. Hallam (BP Resources Canada Ltd.) | G.J.J. Williams (BP Resources Canada Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- May 1990
- Document Type
- Journal Paper
- 163 - 169
- 1990. Society of Petroleum Engineers
- 2.2.2 Perforating, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 5.8.5 Oil Sand, Oil Shale, Bitumen, 5.4.6 Thermal Methods, 1.14 Casing and Cementing, 4.1.2 Separation and Treating, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 2.4.3 Sand/Solids Control, 4.1.5 Processing Equipment
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Data collected at 10 temperature observation wells were analyzed to evaluate the implementation of a combined process of cyclic steam stimulation followed by pressure-up/blowdown combustion for the in-situ recovery of bitumen. The temperature profiles at four observation wells, along the northeast/southwest fracture plane (on-trend direction), confirmed the height and orientation of the vertical fractures during cyclic steam stimulation. Six off-trend wells indicated that the heat transfer away from the fracture plane was predominantly conductive, with varying amounts of convective flow. During the in-situ combustion phase. frontal temperatures greater than 2,200F [1200C] were detected. Data also indicated that the vertical location of the combustion front can be controlled by either gravity or mobility effects. The off-trend heating was improved as a result of higher convective heat fluxes.
The Cold Lake oil sands of east-central Alberta are normally produced by cyclic steam stimulation because the high bitumen viscosity and low fluid mobility inhibit fluid displacement through the reservoir. The cyclic steam process recovers only 15 to 20% of the oil in place. To improve recovery, pressure-up/blowdown combustion has been developed as a follow-up process. The combination of these processes takes advantage of the early production response of cyclic steam stimulation and the potential of high recovery and thermal efficiency of the combustion process. Data from 10 observation wells were analyzed to evaluate the temperature distribution developed by the thermal processes. These profiles are correlated with the reservoir geology, fracture direction, and process operating strategy.
The Clearwater formation, at a depth of about 1,475 ft [450 m], is an unconsolidated sand with several upward-coarsening trends called Sands C1, C2, and C3. Sand C1 has a net pay thickness of 13 ft [4.0 m], a gross thickness of 19 ft [5.9 m], a porosity of 32%, and a bitumen saturation of 58%. This zone contains an occasional interbedded tight streak. Sands C1 and C2 are separated by 12.5 ft [3.8 m] of shale, which frequently is separated into two shale layers by 2.6 ft [0.8 m) of sand. Sand C1 is overlain by 16 ft [4.9 m] of shale that forms an effective seal with the Lower Grand Rapids formation. Sand C2 has a net pay thickness of 9 ft [2.8 ml, a gross thickness of 14.8 ft [4.5 m], a porosity of 29%, and a bitumen saturation of 68%. Horizontal permeabilities are high, but vertical permeability is reduced by up to two tight streaks. Sands C2 and C3 are separated by a thin shale that varies in thickness from 0 to 3 ft [0 to 1 m]. Sand C3 has a net pay thickness of 53 ft [16.2 m], a gross thickness of 65 ft [19.8 m], a porosity of 33%' and a bitumen saturation of 65%. Horizontal permeability is high (1 to 3 darcies) but vertical permeability is reduced by frequent clay laminae and up to three indurated ferroan calcite-cemented layers dispersed within the sand. The lower 9 to 12 ft [3 to 4 m] consists of silts and clays, and the perforated intervals were selected several feet above this zone. The basal shale is more than 10 ft [3 m] thick and forms an effective seal between the Clearwater and McMurray formations. The bitumen has a dead-oil viscosity of 100,000 cp [100,000 mPas] at the original reservoir temperature of 60F [15C]. Field data have shown that the bitumen can be produced when the viscosity is reduced to about 100 cp [100 mPa.s] by heating to 212F [100C].
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