A New Approach to Modeling Miscible Displacement Tests

Abstract

Abstract To develop a design basis for water-alternate-gas miscible flooding with hydrocarbon solvents in two of Esso Resources Canada Limited's carbonate reservoirs, a series of waterflood and tertiary solvent miscible flood core tests were conducted using restored-state composite cores. Because of the major differences in fluid compositions and properties, the tests provided insights into the physics as well as quantified the impacts of water/solvent ratio (WSR), displacement rates and water blockage on ultimate recovery, oil recovery rates and asphaltene precipitation. In both reservoirs, it was observed that water blocking was not significant even at water/solvent ratios as high as 5. Ultimate residual oil saturations that resulted in the tertiary miscible floods were dependent on the amount of asphaltene precipitation. In addition, when it occurred, permeability reduction due to asphaltene precipitation showed the largest effects under pure solvent injection conditions. Simulations of each waterflood and the subsequent tertiary floods using the Tqdd-Longstaff mixing parameter model were conducted, and led to a methodology that enabled both oil recovery and pressure drop data to be matched. It was possible to apply the waterflood relative permeabilities to match the tertiary flood performances. For one of the reservoir fluids that was characterized by the larger amount of asphaltene precipitation, a new asphaltene precipitation model was developed that provided additional quantification of the permeability reduction process.