Simulation of optimal peak oil production rate in a fractured reservoir during miscible CO<inf>2</inf> flooding

Increasing oil prices and depleting domestic resources have generated interest in Enhanced Oil Recovery (EOR) methods. Many EOR methods are currently being used, and CO2 flooding is of great interest, particularly in fractured reservoirs as it not only increases the ultimate recovery but also reduces greenhouse emissions allowing companies to earn carbon credits. In general, primary recovery based on the natural energy of reservoir can produce only 33% of original oil in place (OOIP), while secondary recovery methods based on gas and water flooding can enhance it to 66% in non-fractured reservoirs. However, in fractured reservoirs, gas/water bypass the resident fluid residing within the low-permeability rock-matrix due to the marked difference in porosity and permeability between fracture and its associated rock matrix, and eventually, provides poor sweep efficiency. Thus, fractured reservoirs have always been considered as poor candidates for EOR as these high permeability fractures provide a preferential pathway for injected fluids to channel through directly from injection to production wells without significant fracture-matrix interaction. In the present study, Computer Modeling Group (CMG - GEM) and WINPRO reservoir simulators are used to perform CO2 injection experiments numerically using the concept of "dual-porosity" with different CO2 injection rates and eventually to determine the optimal peak oil production rate during CO2 fluid injection within a fractured reservoir process in a single fracture. Through simulation, sensitivity analysis is conducted to determine the effect of parameters like fracture permeability, matrix porosity, matrix permeability, fracture spacing and fluid velocity on oil recovery factor. Results suggest that oil recovery in case of fractured reservoir is significantly greater than that in a non fractured reservoir or porous reservoir. Copyright 2011, Society of Petroleum Engineers.