Experimental Study on Spontaneous Imbibition of CO₂-Rich Brine in Tight Oil Reservoirs

Abstract

This paper focuses on the CO 2 -EOR in fractured tight oil reservoirs after water-flooding treatment. In previous works, few studies were presented about the spontaneous imbibition experiments of CO 2 -rich brine at formation pressure. We investigated the influence of CO 2 injection on spontaneous imbibition, which is an essential mechanism to improve oil recovery in tight reservoir. In this paper, a laboratory equipment was set up to conduct spontaneous imbibition experiments at formation temperature of 65 °C and pressures of 10−22 MPa on different low-permeability core samples from Nugget, Kentucky, Colton, and Crab-Orchard in the United States. Moreover, we proposed a saturation-based dimensionless time model to scale the spontaneous imbibition and a modified Ma model to fit the oil recovery curves of spontaneous imbibition of CO 2 -rich brine with double peaks of imbibition rate. The results of quantitative imbibition experiments confirm that both the oil production per unit area and the oil recovery have a positive proportional relationship with permeability. A primary reason is that both the capillary pressure and the viscous resistance increase with decreasing of capillary size, but the viscous resistance is more sensitive. The result also quantitatively demonstrates that both the oil production and the oil recovery increase with confining pressure, especially when the pressure exceeds minimum miscibility pressure. However, the pendent drop test illustrates that CO 2 decreases the oil−water interfacial tension with the elevating of pressure. CO 2 can improve the recovery of tight oil by spontaneous imbibition in two main mechanisms: decreasing oil viscosity to improve flowing ability and oil swelling to enhance the cocurrent imbibition. This work provides theory basis and feasible measure for CO 2 -EOR in the fractured and water-flooded tight reservoir.

Phase-Field Modeling of Pore-Scale Oil Replacement by Spontaneous Imbibition in Fractured Porous Media

“…By comparing the numerically simulated results obtained in this study with the existing experimental and simulation data, it can be concluded that the variations of imbibition recovery and imbibition rate under the influences of rock wettability, oil–water viscosity ratio, interfacial tension, and microfractures have the same trend as the previous studies, − ,− which further extend the broad scope of application of the method.…”

Investigation of the Combination Mechanism of Spontaneous Imbibition and Water Flooding in Tight Oil Reservoirs Based on Nuclear Magnetic Resonance

“…Researchers subsequently conducted extensive experiments to assess the impact of matrix and fluid characteristics on spontaneous imbibition. These characteristics include porosity, permeability, viscosity, interfacial tension (IFT), wettability, mineral composition, fluid chemical composition, boundary conditions, and salinity [9][10][11][12][13][14][15][16]. These studies have led to continuous enhancements in the models of spontaneous imbibition.…”

Mechanisms of Imbibition Diffusion and Recovery Enhancing of Fracturing Fluids in Tight Reservoirs

“…The investigation performed by Wang et al explored the influence by surfactants on the imbibition process in tight reservoirs. The results demonstrate that altering the capacity of a surface to be wetted and reducing the force between two interfaces can improve the extraction of fluids by capillary action in low-permeability reservoirs. − Khosravi performed an experiment to investigate the capacity of ionic surfactants to be assimilated by the surfaces of rocks and evaluated their influence on imbibition recovery. The findings indicate that the absorption efficiency of the active agent on the rock surface is primarily influenced by electrostatic interactions, leading to an enhancement in imbibition recovery. − Sun et al conducted a mathematical model to examine the impact for interfacial tension on imbibition.…”