Investigation of alkaline-surfactant-polymer flooding in a quarter five-spot sandpack for viscous oil recovery

The alkaline-surfactant-polymer (ASP) flood has been shown in the past to reduce residual oil saturation significantly after waterflood. ASP floods for light oils are designed to be stable where the mobility ratio of the oil bank to the ASP slug is kept close to one. For viscous oils, such stable recovery processes may be unreasonably slow due higher oil viscosity. The goal of this paper is to study unstable ASP flooding (i.e., oil to ASP slug mobility ratio < 1) in secondary and tertiary modes. A viscous oil of viscosity 100 cp was displaced by an ASP slug in a quarter 5-spot sandpack. The ASP formulation was developed by studying the phase behavior of the oil with several alkaline-surfactant formulations. The effectiveness of the ASP formulation was validated in a 1D sandpack by conducing a water flood followed by a stable tertiary ASP flood. A reservoir sand was used to create a sandpack inside a square steel cell similar to a quarter five-spot pattern. Several ASP floods were then conducted in this cell to study both the displacement efficiency and the sweep efficiency of ASP floods. The tertiary ASP flood recovered most of the oil (similar to 98% of OOIP) when the ASP slug viscosity exceeded the oil viscosity, but pressure gradients were high at similar to 1 ft/d injection. When the ASP slug viscosity was lowered to about 1/3 of the oil viscosity, the oil recovery dropped slightly to 90% OOIP, but the pressure gradient decreased significantly. As the extent of waterflood preceding the ASP flood became shorter, the oil was recovered faster for the same pore volumes injected. The ultimate recovery was independent of the extent of waterflood. The laboratory 5-spot floods were modeled by the simulator UTCHEM. The calibrated simulator can be used at the field scale to determine optimum viscosity ratio and ASP flood timing for viscous oil reservoirs.