Insights Into Water-based EOR Methods In The Water Invaded Zone Of Fractured Reservoirs Using Numerical Simulation

Summary Fractured reservoirs account for most of the hydrocarbon subsurface resources worldwide. Water invaded zone is a specific and important area within the fractured reservoirs where oil can become trapped within the matrix blocks particularly when water passes through the surrounding fracture network. Water-based enhanced oil recovery (EOR) methods can be used to recover the residual oil saturation left within the matrix block located in water invaded zone. In the present study, we attempt to simulate different EOR scenarios including water-alternate-gas (WAG), polymer, surfactant, and low salinity flooding using a conceptual model that is positioned in the water invaded zone and associated with a middle eastern giant oilfield via commercial simulators. First, we report the effects of different parameters including fracture permeability, matrix block height, and injection rate on the extent of different drive mechanisms such as gravity, capillary and viscous forces and further on the ultimate oil recovery and the time required to reach ultimate oil recovery. Then, extensive efforts are made to elucidate the effects of different parameters on the efficiency of each EOR scenario within the defined conceptual model. These parameters include water injection salinity concentration, water injection polymer concentration, water injection surfactant concentration, block height, injection rate, additive (surfactant or polymer) adsorption, water/gas injection duration, and tertiary/secondary schemes. The findings illustrate that in the absence of any viscous forces, capillary and gravity forces both tend to contribute in oil recovery with the capillary and gravity being the dominant force within the early and late time regions, respectively. Sensitivity analysis implies that raising injection rate, decreasing matrix block height, and fracture permeability all lead to an increase in the viscous force, and thus ultimate oil recovery of the matrix block. From the viewpoint of EOR methods, it is generally shown that salt concentration and adsorption of surfactant/polymer additives on the rock surface leave an adverse effect on both the ultimate oil recovery and time required to reach ultimate oil recovery, in contrast to the impact of surfactant/polymer concentration. In addition, the results show that implementing EOR methods as secondary outperforms tertiary schemes as secondary causes the time required to reach ultimate oil recovery sooner. We also report the differences of commercial reservoir simulation packages (ECLIPSE and CMG) and their pros/cons in modeling water-based EOR scenarios. The results of this study help establish a framework for processing each water-based EOR scenario in water-invaded zones of fractured reservoirs.