Numerical Simulation of Natural Fractures on EOR by Cyclic Gas Injection in Unconventional Reservoirs Using DFN Approach

摘要

Major published works on EOR by cyclic gas injection in shale reservoirs have focused on the use of Dual porosity/Dual permeability approach for fracture model development. To adequately account for fluid transport, storage mechanisms, and complex reservoir heterogeneities, natural fractures are modeled using the Discrete Fracture Network (DFN) modeling approach in this study. This allows for discrete modeling of the natural fractures as against an equidistant approach and improves the accuracy of 3D numerical model. A 3D reservoir simulation model was developed for the enhanced oil recovery by cyclic gas injection in a shale reservoir using a commercial simulator. The field 3-D simulation of EOR by cyclic gas injection was carried out using a field in Zavalla County of the Eagle ford shale play. Fracture effectiveness based on fracture contribution to flow was considered in fracture model generation. Using the model the impact of natural fractures is evaluated. The effectiveness of DFN in fractured shale simulation was simulated with cyclic gas injection. The effects of fracture density and orientation of natural fractures, soaking period on ultimate EOR by cyclic gas injection were analyzed. The main driving mechanisms are the oil viscosity reduction and volume swelling. Compared to the conventional Dual porosity/Dual permeability model, the DFN modeling provides a realistic method of evaluating the potential recovery from EOR in shale reservoirs and moves us a step closer to successful field implementation of cyclic gas EORs in shale plays.