Abstract

Waterflooding in a viscous heavy-oil reservoir results in a very poor sweep efficiency because of an unfavorable mobility ratio. However, thickened waterflooding by polymer or gel might not be economic because of high concentrations of chemicals that must be added to achieve a favorable mobility ratio. Moreover, it is understood that thermal recovery cannot be used in thin heavy-oil reservoirs because of major heat loss to overburdened and underburned formations. In cases where an oil reservoir is under permafrost, thermal recovery methods might not be applicable because the injected heat could possibly cause permafrost to thaw. In this paper, it is proposed to inject chemicals (alkaline/surfactant) into a producer immediately after hydraulic fracturing with liquefied propane gas (LPG). The injected chemicals form an oil/water (O/W) microemulsion whose viscosity is much lower than that of the reservoir oil viscosity. When the producer is in production mode, oil is produced in the form of an O/W microemulsion. The interfacial tension between the microemulsion phase and excess oil phase will be very low. Thus, the residual oil saturation will be reduced owing to the increased capillary number. The created hydraulic fractures can provide better access to the reservoir, reduce the loss of the injected chemicals, increase the area of contact between the chemicals and reservoir oil, and improve sweep efficiency of the injected chemicals. The LPG will also work as a solvent during the fracturing phase, speeds up the chemical diffusion and reduce the heavy-oil viscosity around the fracture faces, which will accelerate chemical diffusion when injected after hydraulic fracturing. The chemicals are injected using a huff-and-puff process. Both horizontal and vertical wells can be treated using this process. Simulation results show that the production from such thin heavy-oil reservoirs is significantly accelerated, and the oil recovery factor can be improved up to 200%.

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