Full
Outline
Coal permeability directly affects the efficiency of gas extraction. Using the multiphase and multifield true triaxial dynamic seepage test system of coal and rock, combined with acoustic emission monitoring, ultrasonic testing and high-resolution image processing, the fracture structure and permeability evolution of in-situ coal subjected to hydraulic fracturing with low-concentration ammonium persulfate were investigated, and the influence mechanism of five groups of different liquid injection rates and pressure injection spaces (the action space between fracturing fluid and coal wall in the open hole section) was quantitatively analyzed. The results show that the larger the liquid injection rate is, the shorter the time required for coal to fracture is, the larger the pressure injection space is, the lower the coal fracture pressure is, and the 4-hole fracturing tube (the largest pressure injection space) has the most acoustic emission positioning points and the widest distribution. After hydraulic fracturing, the ultrasonic velocity of five groups of coal samples decreased. Compared with water fracturing, the coal fractured with ammonium persulfate has fewer acoustic emission positioning points (lower damage), but the oxidation and dissolution of ammonium persulfate can further improve the degree of fracture development, and the effect is better in improving coal permeability. Under the same conditions, the larger the pressure injection space is, the wider the range of coal fracture penetration and ammonium persulfate action is, and the more significant the permeability improvement is. When the pressure injection space is the same, the lower the liquid injection rate, the better the permeability improvement effect. The synergistic effect of oxidation dissolution of ammonium persulfate and hydraulic fracturing can promote the expansion of coal fracture network, and the pressure injection space affects the fracture expansion range and density. The research results can provide theoretical guidance for the modification of seepage characteristics of low permeability coal seams.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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