The Impact of the Fracturing Fluid Spontaneous Imbibition on the Petrophysical Properties of Low Permeability Reservoirs

摘要

In the present study, spontaneous imbibition experiments, steady-state permeability measurements, and numerical simulation are integrated to quantify the changes in the effective water permeability, capillary pressure and water relative permeability curves due to the polymer adsorption of the spontaneously imbibed fracturing fluid. The effect of the surfactant and core bedding plane on the fluid spontaneous imbibition volumes were also investigated. The researchers considered a spontaneous imbibition of a 0.1 wt% friction reducer fluid into low- permeability sand core samples extracted from Scioto, Crab Orchard, and Kentucky outcrops. Three comparative systematic spontaneous imbibition experiments were conducted for each of the core samples using distilled water, friction reducer fluid, and distilled water again. Prior to each experiment, the core sample was cleaned with toluene and then dried completely. The core sample water permeability before and after the imbibition experiment was measured using a constant rate steady-state permeability apparatus. The results showed that the polymer adsorption throughout the fracturing fluid spontaneous imbibition significantly reduces the water spontaneous imbibition volumes. Moreover, the polymer adsorption effect increases as the porosity increases. The results showed also that the effective water permeability is decreased because of the polymer adsorption effect. The Residual Resistance Factors calculated from the spontaneous imbibition experiments are in agreement with the values calculated from the constant rate permeability measurements. Adding surfactant to the pad stage- friction reducer fluid increases its spontaneously imbibed (leak-off) volumes. The results showed also that the effect of polymer adsorption on the imbibition rates is significantly less when the rock-fluid contact surface is parallel to the bedding plane. The imbibition potentials were calculated before and after polymer adsorption. Since the water permeability was calculated independently, the capillary pressure curves were calculated from the imbibition potentials. The results showed polymer adsorption leads to a slight increase in the capillary pressure. The spontaneous imbibition experiment is numerically simulated using ECLIPSE commercial simulator and the imbibition water relative permeability curves were calculated by matching the results to the water spontaneous imbibition experimental data. The results showed that the polymer adsorption significantly reduces the water relative permeability curves for Scioto and Crab Orchard.