Investigation and Optimization of the Effects of Geologic Parameters on the Performance of Gravity-Stable Surfactant Floods

Abstract

AbstractA systematic simulation study of gravity-stable surfactant floods has been done to understand the conditions under which it is practical and to optimize its performance. Different optimization schemes have been introduced to minimize the effects of geologic parameters and improve the performance and the economics of surfactant floods. The simulations were carried out using horizontal wells in heterogeneous reservoirs. The results show that gravity-stable surfactant floods can be done at a reasonable velocity and with very high sweep efficiencies for reservoirs with high vertical permeability. These simulations were carried out using a three-dimensional fine grid and a third-order finite-difference method to accurately model fingering. A sensitivity study was conducted to investigate the effects of heterogeneity and well spacing. The simulations were performed using realistic surfactant properties based on laboratory experiments. The critical velocity for a stable surfactant flood is a function of the microemulsion viscosity and it turns out there is an optimum value that can be used to significantly increase the velocity and still be stable. The salinity gradient can be optimized to gradually change the microemulsion viscosity. Another alternative is to inject a low concentration polymer drive following the surfactant slug (without polymer). Polymer complicates the process and adds to its cost without a significant benefit in most gravity-stable surfactant floods, but an exception is when the reservoir is highly layered. The effect of an aquifer on gravity-stable surfactant floods was also investigated and strategies were developed for minimizing its effect on the process.