Deformation mechanism and displacement ability during CO2 displacing CH4 in coal seam under different temperatures

Coupling Mechanism of THMC Fields in Crushed Soft Coal with Low Permeability after CO2 Injection and Its Application in CO2-ECBM Technology

“…The injected CO 2 diffuses backward from the fracture to the pore and adsorbs on the pore surface. According to Fick’s law, the diffusion of binary gases within the coal matrix can be characterized by the following basic relationship: Q s t = prefix− 3 π 2 D i L 2 M g i R T ( P m g i − P f g i ) = prefix− 1 τ i M g i R T ( P m g i − P f g i ) where D i is the diffusion coefficient of i , m 2 /s; L is the cutting width, m; P fgi is the pressure of i in the fracture system, Pa; τ i is the time required for i to desorb 63.2% of the total adsorbed gas during the diffusion process between the matrix and fracture, s.…”

“…The adsorption/desorption process of gas in the matrix is accompanied by an expansion/contraction effect, and the adsorption process of mixed gases follows the extended Langmuir equation. The volume strain caused by gas adsorption follows the following relationship: ε a i = ε L i b i P m g i 1 + falsefalse ∑ j = 1 2 b j P m g j where ε Li is the Langmuir type strain coefficient, which can represent the maximum expansion capacity.…”

Expansion Characteristics and Creep Test of New Curing Expansion Material for Gas Extraction Boreholes

“…The effectiveness of gas control indicates that gas pre-extraction can effectively eliminate the problem of gas concentration exceeding the limit in high-gas mine tunnels, and reduce and eliminate the risk of gas outbursts in the mining face from the source [1][2][3]. After years of research and practice, technologies such as hydraulic fracturing, hydraulic cutting, deep hole blasting, and liquid CO 2 fracturing have achieved certain results in transforming formation stress, expanding the pressure relief range and increasing coal seam permeability [4][5][6][7][8]. However, there are still many problems with the technology and process of gas extraction in Chinese mines at present.…”

Dynamic Response of Gas Recovery Enhancement Efficiency in Coalbed Methane Displacement by Hot Flue Gas: From the Perspective of Thermo–Hydro–Mechanical–Chemical Coupling

“…In contrast, the binary gas mixture (CO 2 /N 2 ) performs well in strengthened gas injection and reservoir permeability recovery, thus bringing about a better gas recovery enhancement effect. , The hot flue gas emitted from gas power plants is actually a nitrogen-rich gas that mainly consists of N 2 , CO 2 , and H 2 O. , Therefore, the injection of hot flue gas into coal seams through surface boreholes can help to increase the gas recovery rate and realize CO 2 geological storage. CBM displacement by hot flue gas (CBMDHFG) involves complex physical and chemical response processes, including the evolution of pore–fracture structure, dynamic evolution of reservoir pressure, multiscale migration of multicomponent gases, migration of gas–liquid two-phase fluid, heat transfer, mineral dissolution, and ion migration. − In fact, these complex physical and chemical response processes are controlled by the interaction among the geomechanical field, gas–liquid two-phase flow field, temperature field, and chemical field during CBMDHFG. Though the multifield coupling model that considers the chemical reactions in CBMDHFG has rarely been mentioned, many meaningful multifield coupling models have been built to describe the complex physical and chemical responses in the coal reservoir during displacement by gas injection.…”