scholarly journals Study on the mechanism of coal-rock interface hindering hydraulic fracture propagation in the process of indirectly fracturing broken soft coal seam

2021 ◽  
Vol 861 (6) ◽  
pp. 062104
Author(s):  
Hao Li ◽  
Weiguo Liang ◽  
YanXia Wu
Keyword(s):  
Coal Seam ◽  
Hydraulic Fracture ◽  
Fracture Propagation ◽  
Soft Coal ◽  
Rock Interface ◽  
Coal Rock ◽  
Hydraulic Fracture Propagation ◽  
Soft Coal Seam

scholarly journals Theoretical Study and Numerical Simulation Research on the Effect of Coal-Rock Interface on Multistaged Fracturing in the Roof of Outburst Coal Seam

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Fan Zhang ◽  
Yang Tang
Keyword(s):  
Elastic Modulus ◽  
Coal Seam ◽  
Hydraulic Fracture ◽  
Mechanical Parameters ◽  
Multiple Fractures ◽  
Rock Stratum ◽  
Gas Drainage ◽  
Rock Interface ◽  
Coal Rock ◽  
Outburst Coal Seam

Multistaged fracturing in the roof of outburst coal seam is an efficient and creative technology for coalbed methane (CBM) drainage, which can effectively improve the permeability of coal seam. To reveal its mechanism of permeability enhancement, the effect of coal-rock interface on multistaged fracturing in the roof of outburst coal seam was simulated and discussed in this paper. Firstly, the lithological difference between outburst coal seam and roof was compared, and the concept and significance of multistaged fracturing in the roof of outburst coal seam were explained. Then, the mechanical conditions of multiple fractures in the roof traversing coal-rock interface were analyzed. The effects of mechanical parameters on multiple fractures were numerically simulated. The results indicated that fracturing borehole in adjacent rocks of outburst coal seam is much easier to drill and maintain gas drainage. Considering gas drainage efficiency and avoiding being blocked by coal fines, multistaged fracturing borehole is generally drilled in the stable rock stratum of roof. Whether the multiple fractures in the roof can traverse coal-rock interface is related to mechanical parameters of coal and rock, friction factor of coal-rock interface, angle between horizontal profile and coal-rock interface, cementing strength of coal-rock interface, minimum horizontal stress, and other factors. Higher fracturing fluid pressure contributes to propagating from the reservoir with low elastic modulus to the one with high elastic modulus for hydraulic fracture. Hydraulic fracture is more likely to propagate in the rock stratum with high brittleness index. The research results can improve multistaged fracturing theory and provide technological support for field test.

scholarly journals Research and Application of Hydraulic Punching Pressure Relief Antireflection Mechanism in Deep “Three-Soft” Outburst Coal Seam

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Beifang Gu ◽  
Yanling Wu
Keyword(s):  
Coal Seam ◽  
Large Scale ◽  
Water Pressure ◽  
Pressure Relief ◽  
Gas Drainage ◽  
Technical Problems ◽  
Soft Coal ◽  
Coal Rock ◽  
Outburst Coal Seam ◽  
Soft Coal Seam

To solve the problems of gas predrainage in deep seams with “three softs” and low-air permeability, hydraulic punching pressure relief antireflection technology is proposed on the basis of the research background of gas predrainage technology in Lugou Mine to alleviate technical problems, such as low gas drainage efficiency, in this mine. Through the analysis of the mechanism of hydraulic punching and coal breaking, combined with FLAC3D software, a hydraulic punching pressure relief antireflection model is established. Then, the fracture radii of coal rock are simulated and calculated. The results show that, under hydraulic punching with a water pressure of 10 MPa and coal outputs of 3 m3, 6 m3, 9 m3, and 12 m3, the fracture radii of coal and rock are 3.4 m, 4.8 m, 5.5 m, and 5.9 m, respectively. Using the software to fit the relationship between coal output V and hydraulic punching fracture radius R under the same water pressure, R = 2.32479 V0.3839 is obtained. The field test is carried out in the bottom drainage roadway of 32141 in Lugou Mine. The application effect is as follows: the gas concentration of hydraulic punching with a coal output of 3 m3 is twice that of ordinary drilling, and the coal output of hydraulic punching with a coal output of 6 m3 is four times that of ordinary drilling. The extraction concentration is four times that of ordinary drilling, and the extraction concentration of hydraulic punching with a coal output of 9 m3 is 6.4 times that of ordinary drilling. Combining the results of the numerical simulation and taking into account the actual construction situation on site, the coal output of water jetting from the borehole is 9 m3, and the fracture radius is 5.5 m. This outcome means that the effective half radius is 5.5 m, and the borehole spacing is 7.7 m. These values are the construction parameters for large-scale applications. This proposal provides effective technology and equipment for gas drainage in the deep three-soft coal seam. Consequently, it has promotion and reference significance for gas drainage in coal seam of the same geological type.

The New Technology of Hydraulic Fracturing Soft Coal Rock Permeability Improvement

2014 ◽  
Vol 1030-1032 ◽  
pp. 1255-1259 ◽  
Author(s):  
Xue Xi Chen ◽  
Yan Ke Zhang ◽  
Yong Xu ◽  
Rui Qing Bi
Keyword(s):  
Coal Seam ◽  
New Technology ◽  
Water Injection ◽  
Injection Pressure ◽  
Field Application ◽  
Good Effect ◽  
Gas Extraction ◽  
Soft Coal ◽  
Coal Rock ◽  
Soft Coal Seam

According to the low intensity, good plasticity in soft coal seam, the effect of direct fracturing to increase permeability was not ideal, the new technology of hydraulic fracture soft coal rock was proposed, which increased coal seam permeability. Its technical principles and characteristics were researched. Water injection pressure was analyzed, including injection time, parameters of the technology and so on. Field application experiment and effect of inspection were conducted. The results showed that the concentration of gas extraction increased 4.3 times, and the gas extraction flow increased 6.2times. The technology has a good effect of fracturing and advantages in enlarging the released area and decreasing diffusion seepage resistance of coal seam. Most important, the technology has broad application prospects in soft coal seam.

Natural fractures in soft coal seams and their effect on hydraulic fracture propagation: A field study

2020 ◽  
Vol 192 ◽  
pp. 107255 ◽  
Author(s):  
Shuaifeng Lyu ◽  
Shengwei Wang ◽  
Xiaojun Chen ◽  
Suifeng Wang ◽  
Tao Wang ◽  
...  
Keyword(s):  
Field Study ◽  
Hydraulic Fracture ◽  
Fracture Propagation ◽  
Natural Fractures ◽  
Coal Seams ◽  
Soft Coal ◽  
Hydraulic Fracture Propagation

Numerical Simulation of Hydraulic Fracture Propagation Characteristics of Low Permeable Coal-Rock Mass

2012 ◽  
Vol 482-484 ◽  
pp. 1668-1671 ◽  
Author(s):  
Zhi Gang Yuan ◽  
Hong Tu Wang ◽  
Nian Ping Liu
Keyword(s):  
Rock Mass ◽  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Fracture Propagation ◽  
Injection Pressure ◽  
Horizontal Stress ◽  
Propagation Model ◽  
Fracture Length ◽  
Coal Rock ◽  
Hydraulic Fracture Propagation

Based on the coal-rock mass deformation model, hydraulic pressure descent model in fracture, fracture propagation model and its growth criterion, the mathematical model of hydraulic fracturing of low permeable coal-rock mass is established, and the influencing factors such as injection pressure, elastic modulus of coal-rock mass and in-situ stress, which affect the characteristics of hydraulic fracture propagation, are studied using the ANSYS software. The results show that fracture length presents a linear increase and widest width increases as an exponent function with the increase of injection pressure, and the ability of making fracture width is greater than fracture length during late fracturing; besides, with the increase of Young’s modulus of coal-rock mass and least horizontal stress, fracture length and widest width decrease, which are independent of maximum horizontal stress. The obtained conclusions provide a guiding role for the optimization of operation parameters of field hydraulic fracturing of low permeable coal-rock.

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