Abstract
High-energy gas fracturing (HEGF) and gas fracturing (GF) are considered to be efficient to enhance the permeability of unconventional gas reservoir. The existing models for HEGF mainly focus on the dynamic loading of stress wave or static loading of gas pressurization, rather than on the combined actions of them. Studies on the combination of HEGF and GF (HEGF+GF) are also few. In this paper, a damage-based stress wave propagation-static mechanical equilibrium-gas flow coupling model is established. Numerical model and determination of mesomechanical parameters in finite element analysis are described in detail. Numerical simulations on crack evolution under HEGF, GF, and HEGF+GF are carried out, and the impact of in situ stress conditions on crack evolution is discussed further. A total of 11 cracks with length of 2.3-4 m in HEGF, 4 main cracks with length of 6.5–8 m in GF, and 11 radial cracks with length of 2–11.5 m in HEGF+GF are produced. Many radial cracks around the borehole are formed in HEGF and extended further in GF. The crustal stress difference is disadvantageous for crack complexity. This study can provide a reference for the application of HEGF+GF in unconventional gas reservoirs.
Highlights
As an efficient clean resource, unconventional gas, such as shale gas and coal bed methane, is of great significance to the sustainable development of economy and energy [1,2,3,4,5]
Alternatives to water for well fracturing, such as explosive fracturing (EF), high-energy gas fracturing (HEGF, high-pressure gas produced from burning a propellant), and gas fracturing (GF, high-pressure gas produced from compressing air) are considered to be potentially efficient to enhance shale gas and coal gas extraction
Loading curves at steps 1-200 shown in Figure 5 are applied to simulate the damage evolution during High-energy gas fracturing (HEGF)
Summary
As an efficient clean resource, unconventional gas, such as shale gas and coal bed methane, is of great significance to the sustainable development of economy and energy [1,2,3,4,5]. The economic viability of developing unconventional gas depends on the effective stimulation of the reservoirs [6,7,8,9,10]. Hydraulic fracturing (HF) has been used widely to enhance production and has been proven successful in most oil, conventional gas and unconventional gas reservoirs. Alternatives to water for well fracturing, such as explosive fracturing (EF), high-energy gas fracturing (HEGF, high-pressure gas produced from burning a propellant), and gas fracturing (GF, high-pressure gas produced from compressing air) are considered to be potentially efficient to enhance shale gas and coal gas extraction
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