Study of Mechanisms of Enhanced Oil Recovery by Multi-Thermal Fluids

Abstract

A new process using multi-thermal fluids as an innovative technique for recovery of offshore heavy oil has been used in Bohai oilfield pilot tests. However, the mechanisms of its enhanced oil recovery and reservoir adaptability (sensitivity) have not been studied in depth. Through theoretical, numerical simulation and experimental analyses, the stimulation mechanisms of various components in this process and the coupling effects between these components in terms of enhanced oil recovery are studied and analyzed in detail. In addition, using oil viscosity, rock permeability and heterogeneity parameters of heavy oil reservoirs in the Bohai oilfield, production results and adaptability to reservoir conditions between the standard steam stimulation process and the stimulation process of multi-thermal fluids are compared. The results indicate that the latter process can enlarge the radius of a thermally swept volume, increase formation energy, and reduce heat loss, but the total enthalpy carried by this process drops slightly. Consequently, the process of multi-thermal fluids stimulation is more suitable to heavy oil reservoirs whose oil viscosity is not too high, heterogeneity is relatively weak, oil formation is thin and natural energy is low. Key words: Offshore heavy oil reservoirs; Multi-thermal fluids; Cyclic steam stimulation; Stimulation mechanism; Production efficiency; Reservoir adaptability; Bohai oilfield