Simulation Study of In-Depth Gel Treatment in Heterogeneous Reservoirs with Sensitivity Analyses

Abstract

Abstract In-depth gel treatment has become an attractive and optimum technology for remedying any problems that cause poor sweep efficiency, such as heterogeneity of the reservoir and unfavorable mobility ratio (due to high oil viscosity). The low recovery factor resulted from the difference in reservoir properties especially reservoir permeability, would lead eventually to use of the chemical materials such as polymer and gel to correct this condition. A comprehensive simulation study of deep placement of weak gel in thick heterogeneous reservoir is presented in this paper. A conceptual model with quarter of inverted nine spot pattern using CMG-STARS commercial simulator was built, to demonstrate the effectiveness of in-depth gel treatment in correcting the heterogeneity in this thick reservoir. The model consists of one injector and three producers with three layers of different permeabilities and thicknesses. These wells are perforated in all layers of the model (i.e., layers 1, 2, & 3). The results showed that injecting even a low PV of gel into high permeability layers could make a remarkable increase in oil recovery factor and incremental oil over the base case water flooding. Polymer and gel degradation rate have a significant impact on the reservoir performance after the treatment. Three different scenarios for both polymer and gel degradation are considered: no degradation, 2 years and 4 years degradation. The results were showed that always the runs without degradation yielded higher recovery factor regardless the injected PV. In addition, when gel is injected into only high permeability layers a higher incremental oil and higher oil recovery factor were obtained in comparison with runs when gel is injected into all three layers. Moreover, the more homogeneous the reservoir is, the higher recovery factor could be obtained. However, in this study, changing the crossflow (kv/kh) value has no effect on oil recovery values over the ranges selected (i.e., 0.001, 0.005, 0.01, and 0.02). The best time to start gel injection is also investigated, it was revealed that it is better to start gel treatment when water cut is about 80%, because before that time the high permeability layers may still contain a moveable oil that can be recovered. Another set of runs were carried out to show the importance of injecting polymer and gel together. The results showed that when gel is injected into all three layers with 4 years gel degradation and 2 years polymer degradation, polymer flooding then gel treatment yielded better results than gel treatment then polymer flooding. Finally, a sensitivity analyses, by CMG-CMOST, was carried out to show the importance of in-situ parameters (i.e., k1, k2, k3, kv/kh, RRFT, and thicknesses of the layers) and operating parameters (i.e., polymer properties, injection pressure, and injection time) on cumulative oil production and oil recovery factor. An optimum values have been obtained that yielded the highest cumulative oil production and highest oil recovery factor. All gel treatment runs had been compared with water and polymer flooding to evaluate the diversion potential of in-depth gel treatment.