Modeling Water Imbibition and Penetration in Shales: New Insights into the Retention of Fracturing Fluids
Feng Yang, He Zheng, Qiulei Guo, Bin Lyu, Sijia Nie, Huan Wang
Abstract
Understanding the penetration and retention of fracturing water in geological systems is important for hydrocarbon extraction and fluid disposal during hydraulic fracturing. This paper explores the imbibition of fracturing water and its penetration profiles on shales from Sichuan Basin, China. Water imbibition experiments were performed on the collected shales with a variety of mineralogical compositions and pore structure characteristics. Sorptivity, quantitatively characterizing water imbibition capacity, was evaluated and its dependence on rock fabric and mineralogical compositions was examined. Then, a nonlinear diffusion model is presented to simulate the capillary flow during the water imbibition process according to the unsaturated flow theory. The solution of this model offers quantitative information about water penetration and distribution in shales. The water sorptivity of shales ranges from 0.1 to 1.8 × 10–6 m/s0.5. Water imbibed by shales is mainly along the shale lamination and bedding. The strong mineral alignment also contributes to sorptivity because of the preferential transport pathways. Shales with developed microfracture networks have higher sorptivity. Nevertheless, water penetration into shales is commonly less than 5 cm during the typical shut-in period after fracturing operations. The fracturing fluid loss is related to the development of microfracture networks and the fracture width. The complex fracture networks with a small fracture width result in low water recovery.