Numerical Simulations of Fracture Propagation in Jointed Shale Reservoirs under CO₂ Fracturing

Abstract

Water-based hydraulic fracturing for the exploitation of shale gas reservoirs may be limited by two main factors: (1) water pollution and chemical pollution after the injection process and (2) permeability decrease due to clay mineral swelling upon contact with the injection water. Besides, shale rock nearly always contains fractures and fissures due to geological processes such as deposition and folding. Based on the above, a damage-based coupled model of rock deformation and gas flow is used to simulate the fracturing process in jointed shale wells with CO 2 fracturing. We validate our model by comparing the simulation results with theoretical solutions. The research results show that the continuous main fractures are formed along the direction of the maximum principal stress, whilst hydraulic fractures tend to propagate along the preexisting joints due to the lower strength of the joints. The main failure type is tensile damage destruction among these specimens. The preexisting joints can aggravate the damage of the numerical specimens; the seepage areas of the layered jointed sample, vertical jointed sample, and orthogonal jointed sample are increased by 32.5%, 29.16%, and 35.05%, respectively, at time t = 39 s compared with the intact sample. The preexisting horizontal joints or vertical joints promote the propagation of hydraulic fractures in the horizontal direction or vertical direction but restrain the expansion of hydraulic fractures in the vertical or horizontal direction.

Phase‐Field Simulation of Hydraulic Fracturing by CO2, Water and Nitrogen in 2D and Comparison With Laboratory Data

“…The damage variable is determined by comparing principal strain to maximum tensile or compressive strain based on failure criteria. The Young's modulus and permeability in the transition zone from rock to fracture is described as a function of the damage variable (Liu, Zhu, et al., 2018; J. Wang et al., 2017; J. G. Wang & Zhang, 2018; Q. Zhang et al., 2019). However, the failure criteria are based on the stress response.…”

Geological built and potential CCS perspectives in northern Poland

“…There are two groups of methods that use carbon dioxide in the hydraulic fracturing process (Labuda 2014). The first of them, currently often used in shale gas extraction in the USA, is based on the utilization of so-called energized fluidsingredients preventing by receding of the space between clay particles in shale and with water and a small or large addition of carbon dioxide in the liquid state (Wang et al 2020;Li et al 2015;Zhang et al 2019). The second, patented in 2013 (Middleton et al 2014;Watts and Watts 2015), assumes the use of carbon dioxide itself, using the fact that, as it moves from liquid to gaseous CO2, it increases its volume and protects spaces in the shale rock before reducing them.…”

Coupled Thermo-Hydro-Mechanical-Chemical Modeling of Permeability Evolution in a CO2-Circulated Geothermal Reservoir

“…where σ ij is the component of the stress tensor and f i is the component of the body force. The poroelastic response, including thermal expansion effects, defines the constitutive relation for the deformable porous medium as follows [26][27][28]:…”