Hydraulic flushing in soft coal sublayer: Gas extraction enhancement mechanism and field application

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.

Download Full-text

A Novel In-Seam Borehole Discontinuous Hydraulic Flushing Technology in the Driving Face of Soft Coal Seams: Enhanced Gas Extraction Mechanism and Field Application

Rock Mechanics and Rock Engineering ◽

10.1007/s00603-021-02691-w ◽

2021 ◽

Author(s):

Hao Zhang ◽

Yuanping Cheng ◽

Cunbao Deng ◽

Longyong Shu ◽

Zhejun Pan ◽

...

Keyword(s):

Field Application ◽

Gas Extraction ◽

Coal Seams ◽

Extraction Mechanism ◽

Soft Coal

Download Full-text

Coupling numerical model of hydraulic fracturing seepage in soft coal based on elastoplastic damage

E3S Web of Conferences ◽

10.1051/e3sconf/202019801038 ◽

2020 ◽

Vol 198 ◽

pp. 01038

Author(s):

LI Liangwei

Keyword(s):

Numerical Simulation ◽

Numerical Model ◽

Hydraulic Fracturing ◽

Yield Criterion ◽

Calculation Model ◽

Field Application ◽

Soft Coal ◽

Plastic Shear Strain ◽

Strain Relationship ◽

Relationship Equation

In order to guide the field application of hydraulic fracturing of soft coal in coal mine, based on the elastic-plastic damage theory, the coupling numerical model of soft coal hydraulic fracturing seepage was studied. The porosity strain relationship equation, permeability strain relationship equation, the relationship between permeability and volume plastic tensile strain and volume plastic shear strain of coal and rock mass are derived, and the plastic correction equation and softening parameters are defined. The stress coupling equation and yield criterion are programmed and embedded into the finite difference software FLAC3D for numerical solution. The numerical simulation shows that the numerical calculation model of soft coal hydraulic fracturing conforms to the actual law, and the field fracturing radius investigation experiment is consistent with the numerical simulation results.

Download Full-text

Investigation of Large-Diameter Borehole for Enhancing Permeability and Gas Extraction in Soft Coal Seam

Geofluids ◽

10.1155/2020/6618590 ◽

2020 ◽

Vol 2020 ◽

pp. 1-13

Author(s):

Yongwen Wang ◽

Wanjun Yan ◽

Zhongjiu Ren ◽

Zhiqiang Yan ◽

Ziwen Liu ◽

...

Keyword(s):

Coal Seam ◽

Shear Failure ◽

Large Diameter ◽

Gas Content ◽

Gas Extraction ◽

Extraction Area ◽

Damage Area ◽

Soft Coal ◽

Coal Deformation ◽

Soft Coal Seam

The efficiency of gas extraction from the soft coal seam with ultralow permeability is low. Gas extraction with large-diameter borehole is proposed to deplete gas content for preventing gas outburst disaster in this study. The fractures around the large borehole will enhance the permeability in the damage area to promote gas extraction. We established a damage-stress-seepage coupling model for large-diameter borehole gas extraction in soft coal seam. This mathematical model contains governing equations of gases sorption and transport, coal deformation, and damage, reflecting the coupling responses between gas and coal seam. The model is solved by the finite element method to simulate the gas drainage large-diameter borehole through roadway. Distributions of elastic modulus, damage area, and maximum principal stress in soft coal seam with different borehole diameters including 94 mm, 133 mm, 200 mm, and 300 mm are analyzed. The gas pressure, gas content, and effective extraction area in soft coal seam are discussed. Results show that the shear failure zone appears around the large-diameter borehole, and its permeability rises sharply. This opens up the gas transport channel and is conducive to the rapid extraction. It is confirmed that gas extraction using large-diameter borehole (300 mm) can greatly improve the efficiency of the gas preextraction in soft coal seam by increasing gas extraction rate. These provide a foundation for guiding the operation of gas extraction with large borehole from the soft coal seam in the field.

Download Full-text

Optimization on Gateway Section of Soft Coal Seam and Hard Roof and Supporting Technology

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.90-93.622 ◽

2011 ◽

Vol 90-93 ◽

pp. 622-625

Author(s):

Lu Chen ◽

Chuan Wei Zang ◽

Feng Hai Yu ◽

Xiang Kun Yu

Keyword(s):

Plastic Zone ◽

Coal Seam ◽

Field Application ◽

Geological Condition ◽

Hard Roof ◽

Soft Coal ◽

Production Safety ◽

Geological Conditions ◽

The Stability ◽

Soft Coal Seam

Support invalidity of a roadway have a largely influence on production safety of coal mines, especially the soft coal roadway, which deforms heavily. To solve this problem, it began from the gateway section optimization, based on the actual geological condition of Chang-gouyu Mine. The computational model was established up to optimize tunnel shapes using FLAC3D. The scopes of plastic zone, stress field, displacement field were compared and analysed for different shapes of roadway. The irregular trapezoid section is adopted, then the bolt support parameters were designed and field application was done. By using the irregular trapezoid, the stress distribution around the roadway is improved and the deformation and plastic zone is decreased. Under the geological conditions of the soft coal seam and hard roof strata, the stability of roadway was effectively controlled by using optimized trapeziform cross-section and bolting support.

Download Full-text

A new method for layout layer optimization of long horizontal borehole for gas extraction in overlying strata: a case study in Guhanshan coalmine, China

10.21203/rs.3.rs-759379/v1 ◽

2021 ◽

Author(s):

Wenbing Guo ◽

Mingjie Guo ◽

Ruifu Yuan ◽

Gaobo Zhao ◽

Guofu Li ◽

...

Keyword(s):

Physical Simulation ◽

Accumulation Rate ◽

Engineering Application ◽

Spatial Location ◽

Theoretical Method ◽

Field Application ◽

Gas Extraction ◽

Fracture Permeability ◽

Borehole Stability ◽

Overlying Strata

Abstract The large emission of pressure-relief gas in coal mining will cause atmospheric greenhouse effect. Arranging long horizontal borehole (LHB) to extract the gas is an effective solution. However, the determination of LHB layout layer in strata has a decisive effect on efficient gas extraction. A "zone-block" theoretical method for determining the LHB layout layer, in present study, was proposed by combining physical simulation test, theoretical analysis and engineering application. Three processes of the method were presented. Firstly, stable fractured subzone (SFSZ) was the optimum zone of the LHB layout based on the analysis of mining-induced fractures distribution and the borehole stability, and spatial location boundaries of the SFSZ in overlying strata were defined. Secondly, the SFSZ was divided into nine-grid blocks, the LHB layout suitability rate of each block were determined according to borehole stability rate, fracture permeability rate and gas accumulation rate. Finally, the LHB drilling could be conducted sequentially according to the layout suitability rate of each block in SFSZ. Field application results show that: the maximum and average amount of pure gas extracted through single borehole arranged in block I can reach up to 5.52 and 2.43 m3·min-1, respectively; and the pure amount in the entire extraction stage of the borehole is 2.53 and 6.69 times of boreholes arranged in blocks II and III, respectively. The proposed method can effectively determine the LHB layout layer in strata, so as to improve the gas extraction efficiency and ensure safe and green mining.

Download Full-text

Influence of Coal Rock Hardness and Confining Pressure on load Fluctuation Characteristics of PDC bit during Gas Extraction Borehole in Soft Coal Seam

International Journal of Advanced Engineering Research and Science ◽

10.22161/ijaers.4.8.8 ◽

2017 ◽

Vol 4 (8) ◽

pp. 44-48

Author(s):

Shifeng Wang ◽

Xiaoming Han ◽

Qiangqiang Zhang ◽

Jialiang Li ◽

Detuo Chene

Keyword(s):

Coal Seam ◽

Confining Pressure ◽

Gas Extraction ◽

Rock Hardness ◽

Soft Coal ◽

Load Fluctuation ◽

Pdc Bit ◽

Coal Rock ◽

Soft Coal Seam

Download Full-text

Influence of Water Injection Fracturing on Crack Damage in Soft Coal and Application in Gas Extraction

Journal of Power and Energy Engineering ◽

10.4236/jpee.2014.24001 ◽

2014 ◽

Vol 02 (04) ◽

pp. 1-6

Author(s):

Zhirong Wang ◽

Jianshi Jin ◽

Zhongyang Hang ◽

Xiangzhi Hu

Keyword(s):

Water Injection ◽

Gas Extraction ◽

Soft Coal ◽

Influence Of Water

Download Full-text

New Method for Reducing Coal Mine Gas Disasters via Directional Drilling and Hydraulic Jet

10.21203/rs.3.rs-951390/v1 ◽

2021 ◽

Author(s):

Dingqi Li ◽

Shuren Wang ◽

Yubo Chen ◽

Mingzhong Wang ◽

Xu Chang

Keyword(s):

Coal Seam ◽

Coal Mine ◽

New Method ◽

Equivalent Diameter ◽

Gas Extraction ◽

Drilling Machine ◽

Directional Drilling ◽

Soft Coal ◽

Porosity And Permeability ◽

The Cost

Abstract Gas extraction is an important topic because of poor permeability and high gas seam in coal mines. A new method for reducing stress and improving permeability of coal seam was proposed to reduce the cost of gas extraction and danger of coal and gas outbursts. In this method, the roadway in coal floor was replaced with directional main borehole, directional branch boreholes were used to replace crossing holes, and soft coal was mined along soft sub layers using a directional drilling machine and a directional hydraulic jet. The numerical simulation showed that the porosity and permeability of coal seam significantly improve after soft sub layers being removed by the directional hydraulic jet. The application of the proposed method and its supporting equipment was carried out under the special gas conditions of Hudi Coal Mine. Results show that the soft coal is mined efficiently along the soft sub layer using the main borehole, branch boreholes, and directional hydraulic jet. Compared the hydraulic punching in the borehole with the ordinary drilling machine, the average speed of mining soft sub layers increased from 0.5 t/h to 3.6 t/h, the equivalent diameter of mining soft sub layers increased from 1.2 m to 7.6m, and the average flow of gas extraction increased from 0.41 m3/d to 6.25 m3/d. The conclusions obtained in this study can provide a reference to the similar coal mining methods.

Download Full-text