Abstract
Mining high-gas coal seams in China has the characteristics mining of deep, high storage and low permeability, and low drainage efficiency, which seriously restrict the efficient prevention and control of mine gas disasters. Based on the characteristics of low viscosity and permeability, phase change pressurization, and strong adsorption potential energy of liquid CO2, the technology system of liquid CO2 displacement for high-gas and low-permeability coal seam was developed, and field industrial of low-pressure (0.5~2.5 MPa) and medium-pressure (2.5~15.0 MPa) combined injection test was carried out. In this test, the mode of injection followed by drainage was adopted, and the gas drainage effect was investigated for 30 days. The test results show that the effective influence radius of CO2 in this test is 20 m, and the liquid seepage radius is 5 to 7 m. After the injection of liquid CO2 into coal seam, the average gas drainage concentration and drainage purity of all drainage holes were increased by 3.2 and 3.4 times, respectively, and the gas promotion effect was significant. Taking the liquid CO2 low-medium-pressure displacement gas test area as the calculation unit, from the comprehensive benefit analysis, compared with the original drainage mode, the liquid CO2-combined pressure injection process can save 34.7% of the engineering cost and shorten the gas drainage standard time by 45.9%. Therefore, the application of this technology has important technical support and reference significance for the efficient management of gas in the same type of mine.
Highlights
“High storage and low permeability” is a common attribute of most of the coal seams in deep mines in China
Based on the mechanism of CH4 generation, storage, and migration, increasing coal seam CH4 production mainly starts from two aspects: one is to promote the desorption of coalbed methane, so that the CH4 adsorbed on the inner surface of the coal matrix pores can be changed from the adsorbed state to the free state as much as possible, and the Geofluids diffusion of Coalbed methane (CBM) from the matrix and micropores to the cracks is expanded [5]
Few fundamental studies on enhanced coalbed methane (ECBM) recovery technologies using liquid CO2 have been conducted, and related studies have mainly focused on the promotion of coal seam gas drainage by gaseous and supercritical CO2 [20, 21]
Summary
“High storage and low permeability” is a common attribute of most of the coal seams in deep mines in China. With the importance of environmental protection in China, enhanced coalbed methane (ECBM) recovery technology has become the focus of gas prevention and control. To improve the efficiency of CBM disaster control and reuse in deep well mining, a variety of coal seam permeability enhancement and gas drainage promotion technologies have been developed, mainly including protective layer mining, hydraulic fracturing, hydraulic slotting, highenergy detonation wave blasting fracturing, shock wave fracturing, and liquid CO2 blasting [8,9,10]. From the analysis of the engineering application effect, the above-mentioned technical processes can obviously improve the permeability of the coal seam and achieve the purpose of promoting gas drainage. Few fundamental studies on ECBM recovery technologies using liquid CO2 have been conducted, and related studies have mainly focused on the promotion of coal seam gas drainage by gaseous and supercritical CO2 [20, 21]. The feasibility of the process technology was debugged on site, the key parameters of the field test were investigated, and the comprehensive benefits of the process technology were verified by subsequent gas drainage effects
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