The mechanism of hydraulic fracturing assisted oil displacement to enhance oil recovery in low and medium permeability reservoirs

Abstract

Aiming at the technology of hydraulic fracturing assisted oil displacement which combines hydraulic fracturing, seepage and oil displacement, an experimental system of energy storage and flowback in fracturing assisted oil displacement process has been developed and used to simulate the mechanism of percolation, energy storage, oil displacement and flowback of chemical agents in the whole process. The research shows that in hydraulic fracturing assisted oil displacement, the chemical agent could be directly pushed to the deeper area of the low and medium permeability reservoirs, avoiding the viscosity loss and adhesion retention of chemical agents near the pay zone; in addition, this technology could effectively enlarge the swept volume, improve the oil displacement efficiency, replenish formation energy, gather and exploit the scattered residual oil. For the reservoir with higher permeability, this measure takes effect fast, so to lower cost, and the high pressure hydraulic fracturing assisted oil displacement could be adopted directly. For the reservoir with lower permeability which is difficult to absorb water, hydraulic fracturing assisted oil displacement with surfactant should be adopted to reduce flow resistance of the reservoir and improve the water absorption capacity and development effect of the reservoir. The degree of formation energy deficit was the main factor affecting the effective swept range of chemical agents. Moreover, the larger the formation energy deficit was, the further the seepage distance of chemical agents was, accordingly, the larger the effective swept volume was, and the greater the increase of oil recovery was. Formation energy enhancement was the most important contribution to enhanced oil recovery (EOR), which was the key to EOR by the technology of hydraulic fracturing assisted oil displacement.