Simulation Study of Application of a Water Diverting Gel in Enhanced Oil Recovery

Abstract

Abstract The objective of this research is to widen the understanding of a cost-effective and green hybrid gel system developed for water diversion in waterflood applications in heterogeneous systems characterized by high water cuts. Feasibility of the new gel system is evaluated by investigating its transport through porous medium and the blocking mechanism using numerical simulation studies. It is attempted to present guidelines for selecting the best reservoir candidate and optimum conditions of successful gel application by this research. Comprehensive simulation study of deep placement of a polymer gel system in layered reservoirs is presented in this paper. The controlled release of crosslinkers for delayed gelation is modeled by long half-life of the gelants assuming a simple model of reaction kinetics. Results of the gel injection are compared with water and polymer floods to evaluate the diversion potential of the gel system. Sensitivity analysis is done on several parameters affecting the gelation such as injection concentration, time and gelation rate. Effects of permeability contrast, crossflow, injection strategy and blocking properties on oil recovery are also considered. Mechanisms studied in this work are diversion or blockage and crossflow. Results indicate that high permeability reduction in the thief zone is a necessity to obtain high incremental recovery. In addition, gelation time should be long enough for the gelants to propagate deep into the formation. Blockage or permeability reduction is modelled by adsorption of the gelants or gel. The best results are obtained when the treatment is initiated at the time of water breakthrough. Gel treatment is more effective than polymer flooding considering increased oil recovery and reduced water cut while using less polymer. Polymer flood recovers more oil with high crossflow where the idea is to overcome the layered system heterogeneities. Unlike water and polymer flooding, high crossflow between layers will result in poor sweep efficiency of the gel treatment since more gelants will penetrate the low permeability zone and cause damage. Higher crossflow results in pressure equilibrium between the layers and reduces the possible oil resaturation of the depleted high permeability zone and instead causes additional water crossflow. Increased gel treatment size and injected concentration will result in more recovery; however, an economic analysis seems necessary to define the optimum conditions. This work presents a detailed application study of a new gel system which is based on novel multifunctional hybrid polymers with the ability to control the release of the crosslinkers and delay the formation of the gel for weeks or months. This was made possible by encapsulation of the crosslinkers, and hydrolysis within the requested time window triggers the gelation process. Long gelation times needed for deep penetration previously used in some theoretical studies were however not technically achievable. Another benefit of the gel system discussed here is that unlike many other gel systems, it is environmentally acceptable.