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.