Laboratory investigation of multiphase permeability evolution due to fracturing fluid filtrate in tight gas sandstones.

摘要

Injection of large volumes of fluids during fracture treatment may result in leak-off, capillary imbibition and trapping of the fracturing fluid filtrate in the pores of the reservoir. The trapped fluid affects the mobility of hydrocarbons during clean-up and production. Additionally, the fracturing fluid filtrate near wellbore and fracture region is one of variable composition and can induce alterations in rock-fluid and fluid-fluid interactions. The concomitant changes in multiphase permeability during fluid invasion and clean-up is one that is not fully understood.;The aim of this study is to investigate the role fracturing fluid filtrate composition has on the evolution of multiphase permeability during imbibition and drainage of the aqueous phase. In this work, multiphase flow of fracturing fluid filtrate in low permeability sandstones was investigated by means of laboratory experiments for three commonly employed fracturing fluids. The multiphase flow experiments were conducted using brine, helium and filtrate from various fracturing fluids in sandstones cores of different permeabilities. The alteration of rock-fluid properties and changes in interfacial tension in the presence of gas were determined by evaluation of the obtained relative permeability curves to both gas and liquid/filtrate phase. Experimental results indicate that there was a reduction in end-point and liquid phase relative permeability following imbibition of slickwater into the core sample. The liquid phase relative permeability decreases with increasing concentration of friction reducer (Polyacrylamide solution) present in the fluid system. Adsorption flow experiments with slickwater confirm the adsorption of polyacrylamide molecules to the pore walls of the rock sample and results in increased wettability of the rock sample. This process was found to increase liquid trapping potential of the rock surface. For linear and crosslinked gels, filtrate composition does not have a significant effect on liquid relative permeability during fluid invasion due to limited polymer invasion into the core.;This study also investigated the effect of alcohol and surfactant used as remediation additives on multiphase permeability evolution with different fracturing fluid systems. Multiphase permeability flow tests were conducted to determine, understand and quantify the mechanisms that govern multiphase permeability evolution using alcohols and surfactants to remediate aqueous phase trapping. Methanol and two surfactant chemicals, Novec FC-4430 and Triton X-100 were used as remediation additives in this study.;Results from multiphase permeability flow tests conducted with methanol indicated that the volume of liquid removed by displacement increases with methanol concentrations for all fracturing fluids. This is attributed to increased liquid mobility from addition of methanol during the displacement process. Interfacial tension does not contribute to multiphase permeability during the displacement phase. Additionally, friction reducer alters the flow properties of the trapped liquid as indicated by increased surface tension, lower volumes of liquid removed and lower gas endpoint permeability at the same methanol concentration for cores saturated with slickwater. Majority of the improvement in gas permeability from methanol addition is by evaporation of the trapped liquid phase and is caused by increased volatility of the fracturing fluid. Results from multiphase permeability flow tests conducted with surfactant indicated that multiphase permeability evolution is driven by wettability alteration of the rock surface. Pretreatment of core sample with Novec FC-4430 before flooding with fracturing fluid results in best gas permeability improvement and liquid recovery. Triton X-100 did not improve gas permeability or liquid recovery during cleanup. Findings from this study can be used to optimize fracturing fluid and additive selection for field applications. Multiphase permeability data obtained is also useful for model assisted analysis of post fractured production performance in low permeability reservoirs.