For heavy oils with viscosities ranging from 1,000 to 10,000 mPa·s (cP) in Western Canada, primary production and waterflood together can only recover 8 – 15 % original oil-in-place (OOIP) at their economic limit due to the adverse mobility ratio, severe water channeling and low reservoir pressure and formation voidage. These heavy oils usually have a relatively high content of acids which can react with alkalis to form in-situ surfactants. The loosely consolidated sandstone formations where these oils are deposited are characterized by high porosity, permeability and low reservoir temperature. These reservoir conditions are favorable for polymer application. Therefore, there is a potential to improve waterflood in these reservoirs by applying alkaline/polymer (A/P) flooding.

This paper presents the results of a laboratory study of A/P flooding for heavy oil recovery, including viscosity measurements, flood tests conducted in channeled sandpacks, residual resistance factor (Frr) determination, and residual oil distribution tests. A heavy oil with a viscosity of 1,202 cP and an acid number of 1.07 (mg KOH/g-oil) and produced brine collected from a heavy oil reservoir in Alberta are used in this study. The experimental results show that addition of polymer to alkaline solution reinforces stability and strength of in-situ formed emulsions. It is found that the distribution of the injected chemical solution into the high permeable cannels leads to the diversion of the subsequently injected chemical solution to low permeable zones with higher oil saturation due to the formation of blockage in the channel zones. Consequently, pressure build-up during chemical slug injection is the key to the improvement of displacement efficiency. Flood tests also show that alkaline-polymer flooding is more efficient than either alkaline flooding or polymer flooding. The optimal formulation for the heavy oil used in this study is 0.4% NaOH + 0.2% Na2CO3 + 1,000 mg/l polymer, with a tertiary oil recovery of 25 – 30 % OOIP over waterflood. Analysis of the results of the residual oil distributions in the channeled sandpacks at the end of A/P flooding shows that A/P flooding can effectively improve the sweep efficiency of waterflood for the heavy oil.

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