The forced imbibition model for fracturing fluid into gas shales

Abstract Understanding the factors controlling the fracturing fluid leak-off due to forced imbibition during the hydraulic fracturing operations is critical for the accurate assessment of the fracturing fluid invasion depth and the extent of the formation damage in gas shales. Here, we present results of an experimental and a modeling study of the factors controlling fracturing fluid forced imbibition into the organic rich shale gas reservoirs. The main objectives of the study were to: i-) Experimentally investigate the forced imbibition of the brine and the slick water (SW) into the shale; ii-) Develop an analytical model of the fracturing fluid forced imbibition into the shale matrix. The shale samples collected from Silurian Longmaxi (SL) Shale Formation, which is located in Southern Sichuan Basin in China, were used to conduct the forced imbibition experiments. Effects of varying fluid properties (i.e., the viscosity and the surface tension), the direction of the imbibition with respect to the shale bedding plane/lamination, and the fluid pressure across the shale face on the cumulative mass of the imbibed fluid per unit area over time were investigated. A new analytical model of the forced imbibition into a shale rock was developed. The Hagen-Poiseuille law and the capillary tube bundles model were used to describe flow through tortuous capillary. The new model also considered the effects of the fluid pressure across the rock face (i.e., forced imbibition) and the viscous pressure loss in the capillary. Comparison of the model predictions with the experimental results indicated that the effects of the fluid pressure and viscous pressure loss on the imbibed fluid mass are not negligible. The close agreement with the model predictions and experimental results in the direction parallel to shale lamination confirmed that the new model accurately describes the process of fracturing fluid forced imbibition into the shale matrix in the direction parallel to shale bedding plane. The new model could potentially be used for the field scale prediction of the average depth of fluid invasion into the shale matrix in the direction parallel to lamination due to the forced imbibition of the fracturing fluid.