Modeling Water Leak-off Behavior in Hydraulically Fractured Gas Shale under Multi-mechanism Dominated Conditions

Coupled Thermo-Hydro-Mechanical-Chemical Modeling of Water Leak-Off Process during Hydraulic Fracturing in Shale Gas Reservoirs

“…The following fluid and heat flow equations for water and gas in hydraulically fractured shale reservoirs are the extension of "MMM model", which was developed by Wang et al [37] for the iso-thermal fracturing-fluid leak-off simulation, but without considering the phenomena of water thermal osmosis and rock thermal poroelastic deformation. In this study, the THMC leak-off model is considered as a triple-porosity model including three interconnected domains of hydraulic fractures (F), natural fractures (f ) and matrix (m).…”

“…where p f l and p w f denote the fluid pressure in natural fractures and flowing pressure at the bottom-hole (10 −1 MPa); α 1 and α 3 denote the shape factors between the hydraulic fracture and the natural fracture and the wellbore (cm −2 ), respectively, which are decided as presented in Wang et al [37] and Bian et al [50]; and B l denotes the fluid volume factor (dimensionless).…”

“…The relative permeability of gas-water in F, f and m are set according to a previous simulation case [37]. The empirical equation proposed by Gdanski et al [59] is used to calculate the capillary pressure curves.…”

“…Although many leak-off models have been published based on laboratory experiments and numerical simulation [3,[5][6][7][8][11][12][13][14]16,32,36,37], none of the models coupled the transient fluid flow modeling with natural fracture dilation, heat transfer and chemical-potential equilibrium phenomena. To investigate all of the above-mentioned mechanisms, a coupled thermo-hydro-mechanical-chemical (THMC) model, which is based on our previous multi-mechanistic multi-porosity multi-permeability (MMM) model [37] without considering heat transfer and rock deformation, is developed to simulate the fluid/heat flow during the leak-off process of hydraulic fracturing in this study. Results from this study aim to provide a better understanding of the predominant leak-off mechanisms for slickwater fracturing-fluids in shale gas reservoirs, and therefore contribute to the post-fracturing prediction and evaluation of shale gas wells.…”

Hydrodynamic Equilibrium Simulation and Shut-in Time Optimization for Hydraulically Fractured Shale Gas Wells

“…An increase in capillary force can promote the occurrence of water flowing through porous media and cause a water lock in the matrix, but also reduce the initial gas production; complex fractures can help to increase gas production but reduce flowback rate; and with the increase of shut-in time, gravity differentiation is significant. Wang et al [7] established a numerical model to investigate the chemical osmosis phenomena on fracturing-fluid leakoff during shut-in periods. Their simulation results indicate that chemical osmosis can lead to an extra leakoff volume of 7% .…”