A Thermo-Hydro-Mechanical-Chemical Coupling Model and Its Application in Acid Fracturing Enhanced Coalbed Methane Recovery Simulation

Abstract

The reservoir permeability dominates the transport of gas and water in coal seam. However, coal seams rich in gas usually contain various pores and fractures blocked by a large amount of minerals, which leads to an ultra-low permeability and gas extraction rate, and thus an increase of drilling workload. We first propose a thermo-hydro-mechanical-chemical coupled model (THMC) for the acid fracturing enhanced coalbed methane recovery (AF-ECBM). Then, this model is applied to simulate the variation of key parameters during AF-ECBM using a 2D geometry. The effect of different extraction schedules are comparatively analyzed to give an insight into these complex coupling responses in coal seam. Result confirms that the AF-ECBM is an effective way to increase the reservoir permeability and improve the gas production using the proposed model. The range of permeability increment zone increases most dramatically in the way of acid fracturing, followed by none-acid fracturing and acidizing over time. The gas production in order is: acid fracturing (AF-ECBM) > fracturing (F-ECBM) > acidification (A-ECBM)> direct extraction (D-CBM).

Hydraulic‐Mechanical Coupling Model with Dual‐Porosity Dual‐Permeability for Anisotropy Coal Seams and Its Application in Mine Gas Extraction

“…According to the pore structure characteristics, gas existence, and migration in the coal seam, the following assumptions are drawn [23,32,33]: (1) as shown in Figure 3, the coal seam is regarded as the anisotropic dual-porosity, dual-permeability elastic continuity medium, and the coal seam consists of fractures and coal matrix, while pores exist in the coal matrix; (2) the relationship between adsorbed gas content and gas pressure follows the Langmuir equation; (3) gas is assumed to be satisfied with ideal gas; (4) the coal seam Gas extraction reduces the pressure near borehole which will break the gas adsorption equilibrium in the coal matrix. e absorbed gas desorbs into the space of pores and transports to the fractures driven by the pressure and concentration gradients via diffusion and seepage accordingly [34,35].…”

“…A coupled model was presented to analyze fluid flow and deformation in porous and fractured rock considering the Klinkenberg effect [19][20][21]. e complex coal and gas interactions under variable temperatures were investigated [22][23][24]. Suites of governing equations for the hydraulic-mechanical model including the dual-porosity structure of the coal seam were developed to model the hydraulic fracturing in the coal seam and optimize the enhanced coalbed methane recovery using CO 2 /N 2 mixtures [25][26][27].…”

Experimental study on controlled-release inhibitor foam for restraining spontaneous combustion of coal

“…In major coal producing countries, such as China, the United States, Australia and India, coal fire disasters are very common and are considered as a global disaster problem (Havva, 2007;James et al, 2009;Kong et al, 2017;Mohalik et al, 2017;Parsa et al, 2017;Wang et al, 2018;Yang and Qiu, 2019). More than 95% of Chinese collieries perform underground coal mining, in which fire accidents due to spontaneous coal combustion account for more than 90% of the total number of mine fires (Deng et al, 2008;Fan et al, 2020Fan et al, , 2019. Especially, certain amounts of coal are left in goafs after mining as broken accumulations.…”

Prediction of Residual Gas Content during Coal Roadway Tunneling Based on Drilling Cuttings Indices and BA‐ELM Algorithm

“…With depletion of shallow coal resources, the mining depth of coal mines in China increases. e coupling effect of great in situ stress and high gas pressure in deep coal seam increases the risk of gas outbursts [1][2][3][4][5]. e residual gas content is an important parameter for gas outburst prediction.…”