Evaluation of EOR methods for heavy-oil recovery in naturally fractured reservoirs

When unfavorable conditions such as heavy-oil, large matrix size, high IFT, low matrix permeability, oil-wet matrix and poorly connected fracture network exist in an oil reservoir, additional support to enhance the matrix oil recovery is inevitable. Water and gas can be injected in order for the matrix oil to be recovered by capillary and gravity forces, respectively. These processes may not yield significant recovery increase as matrix oil becomes heavier and less water wet. In this case, thermal, chemical and miscible gas injection can be thought to overcome the limitations. Recent studies and limited number of field applications have shown that those methods might result in substantial amount of additional oil recovery. On the other hand, there exist certain conditions where the methods may not be technically and economically feasible. This paper reviews different EOR methods and the parameters affecting the performance of heavy-oil recovery based on experimental observations. The application conditions from technical and economical points of view are also discussed.