Non-linear seepage model of hydraulic fracturing assisted oil displacement coupled with effects of high-pressure reduced adsorption: A case study of low and medium permeability reservoirs in Daqing Oilfield, NE China

Abstract

Considering the adsorption loss of the hydraulic fracturing assisted oil displacement (HFAD) agent in the matrix, a method is proposed to characterize the dynamic saturation adsorption capacity of the HFAD agent with pressure differential and permeability. Coupled with the viscosity-concentration relationship of the HFAD agent, a non-linear seepage model of HFAD was established, taking into account the adsorption effect of high pressure drops, and the influencing factors were analyzed. The findings indicate that the replenishment of formation energy associated with HFAD technology is predominantly influenced by matrix permeability, fracture length and the initial concentration of the HFAD agent. The effect of replenishment of formation energy is positively correlated with matrix permeability and fracture length, and negatively correlated with the initial concentration of the HFAD agent. The initial concentration and injection amount of the high-pressure HFAD agent can enhance the concentration of the HFAD agent in the matrix and improve the efficiency of oil washing. However, a longer fracture is not conducive to maintaining the high concentration of the HFAD agent in the matrix. Furthermore, the fracture length and pump displacement are the direct factors affecting the fluid flow velocity in the matrix subsequent to HFAD. These factors can be utilized to control the location of the displacement phase front, and thus affect the swept area of HFAD. A reasonable selection of the aforementioned parameters can effectively supplement the formation energy, expand the swept volume of the HFAD agent, improve the recovery efficiency of HFAD, and reduce the development cost.