The explanation of low recovery of fracturing fluid in shale hydraulic fracturing by pore-scale simulation

Abstract

Within the low recovery of fracturing fluid during hydraulic fracturing in shale, the displacement between water and gas is simulated in pore-scale. The lattice Boltzmann model with high-density ratio is employed, and the geometry is three-dimensional shale digital core, which is reconstructed by Markov Chain Monte Carlo method with a high resolution SEM scanning image as input. The model is verified by calculating the surface tension and relative permeability. Water (gas) is saturated at first, and then, gas (water) is injected at inlet. The simulation is terminated when breakthrough of displacement phase occurs at outlet. The kinetic viscosity ratio and density ratio of gas and water are set to 10:1 and 1:1000, respectively. The water saturation is 70% at breakthrough when water displaces gas, while the gas saturation is only 4.5% at breakthrough when gas is advancing phase. The distribution of displacement phase is given in three-dimensional digital core. Most water is trapped in the pore at breakthrough, when water is displaced by gas. Hence, the phenomenon of recovery of fracturing fluid is less than 10% in shale is explained.