Coupled analysis about multi-factors to the effective influence radius of hydraulic flushing: Application of response surface methodology

The effective extraction radius of borehole is the main parameter for determining the design and layout for coalbed methane extraction. This paper is aimed at the problem that the criteria and calculation methods for the effective extraction radius of coal seams are not comprehensive. With Wudong Coal Mine in China taken as an example, the critical gas pressure (0.441 MPa) for the calculation of effective extraction radius is first defined. Next, the gas seepage unit model around the borehole is developed, and the theoretical mathematical expression to calculate the effective extraction radius is derived. Then, the numerical simulation of gas extraction is carried out through a computational fluid dynamics program, and the effective extraction radius is obtained numerically. Furthermore, the influence of original gas pressure, borehole diameter, and negative pressure of gas extraction on gas extraction is analyzed. Finally, the results from the theoretical calculation and numerical simulation are validated by the field engineering measurement and the average relative error is small (less than 10%). The results indicate that the effective extraction radius has a linear relationship with the extraction time. Moreover, it is found that the original gas pressure is the main factor affecting the effective extraction radius and the effective extraction radius is proportional to the borehole diameter and negative pressure through analysis. Therefore, the above findings can provide a theoretical basis for determining parameters such as borehole spacing and extraction time of gas extraction in coal mines.

Section: Theoretical Calculation Of Effective Extraction Radiusmentioning

confidence: 75%

Section: Theoretical Calculation Resultsmentioning

confidence: 99%

Theoretical, numerical, and experimental analysis of effective extraction radius of coalbed methane boreholes by a gas seepage model based on defined criteria

Wang

Chang

et al. 2019

“…At present, methods of coal seam permeability enhancement include N 2 injection, deep hole presplitting blasting, hydraulic fracturing, hydraulic flushing, hydraulic slotting, and other methods . The permeability has shown a trend of increasing sharply, slightly decrease, and then stable at a constant value after injecting N 2 in CO 2 ‐rich low permeable seam .…”

Section: Introductionmentioning

confidence: 99%

“…10,11 Therefore, how to enhance the permeability of coal seam and improve the efficiency of gas drainage, especially complex geological conditions(eg, coal seam with a soft layer), is a difficult problem for experts and scholars all over the world. 12 At present, methods of coal seam permeability enhancement include N 2 injection, deep hole presplitting blasting, 13 hydraulic fracturing, 14 hydraulic flushing, 15,16 hydraulic slotting, and other methods. [17][18][19][20][21][22] The permeability has shown a trend of increasing sharply, slightly decrease, and then stable at a constant value after injecting N 2 in CO 2 -rich low permeable seam.…”

Section: Introductionmentioning

confidence: 99%

A new cross‐borehole hydraulic caving technique in the coal seam with a soft layer for preventing coal and gas outbursts during coal roadway excavation

Qin

Wei

Lou

et al. 2020

Predrainage of gas by cross‐boreholes is an important method to prevent coal and gas outbursts in the process of a coal roadway excavation. Limitations of technologies and poor effects of preventing coal and gas outbursts occur in the coal seam with a soft layer. In this study, a new hydraulic caving technology for cross‐boreholes has been proposed to solve this problem. A CT equipment was used to observe the development of coal fissures around cross‐boreholes in the coal seam with a soft layer. The plastic zone range and permeability distribution of ordinary hydraulic slotting technologies and the new hydraulic caving technology also were compared by numerical simulation. The field test of hydraulic caving was taken in the Xuehu Mine (China). The results show that the fracture development degree of soft coal is greater than that of hard coal at the same distance from cross‐boreholes. The fracture development degree in the plastic zone is greater than that in the elastic zone. The hydraulic caving technique can achieve the same effect as the ordinary hydraulic slotting with less workload. The mass of coal discharged from a cross‐borehole was 1.15 t/m and the average methane concentration of single drainage borehole increased by 1.09‐4.1 times, and the average methane extraction amount of single drainage borehole increased by 6.06 times. Elimination of coal and gas outburst had been completed after 110 days of extraction in the area of hydraulic caving, and Q and S values are lower than the critical value during roadway excavation. It is conclusion that hydraulic caving technique can effectively improve the permeability and rapidly eliminate coal and gas outburst in the coal seam with a soft layer.

“…However, most of the mines in China, India, and a few other countries are in a physical environment of high in situ stress and low permeability, with the mining depth increasing at a rate of 10-25 m/a. [7][8][9][10][11] A series of hydraulic measures, including hydraulic fracturing, [12][13][14] hydraulic slotting, [15][16][17] and hydraulic flushing [18][19][20][21] can promote the development of fractures and pores in the coal reservoir, which effectively improve the gas extraction rate. However, coal seam water injection technology for regional outburst elimination measures was cancelled in the Regulations on Prevention and Control of Coal and Gas Outburst promulgated by the Chinese Government in 2009.…”

Section: Introductionmentioning

confidence: 99%

Response characteristics of the resistivity and water content during the imbibition process in remolded coal without gas

Yue

Wang

Chen

et al. 2019

The water content distribution in a coal body is closely related to the gas distribution. It is difficult to directly determine the water content distribution in the process water imbibition. To retrieve the water content by the resistivity value and establish a relationship between the resistivity and water content, the response characteristics of the resistivity and water content of remolded coal formed under different loads are studied by a self‐designed resistivity experimental system. The results show that the resistivity of the remolded coal decreases over time during the imbibition process, including a rapidly decreasing stage and a slowly decreasing stage. The resistivity of the remolded coal is related to the water in the macropore in the rapidly decreasing stage. In the slowly decreasing stage, the resistivity is related to the contact between coal particles. The pressing load, imbibition range, and imbibition speed are negatively correlated with porosity. The resistivity of the steady state is also negatively correlated with the water content and pressing load. The relationship between the resistivity of the steady state and the water content fit a power function. This study reveals the law of resistivity and the water content during the imbibition process and provides an effective methodology to bridge the gap for measuring water content distribution during the imbibition process.