Experimental investigation of flow regime transition characteristics of fractured coal bodies around gas extraction boreholes

Pang, Mingkun; Pan, Hongyu; Ji, Bingnan; Zhang, Hang; Zhang, Tianjun

doi:10.1016/j.energy.2023.126758

Cited by 11 publications

(4 citation statements)

References 22 publications

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“…① Gas in the coal body around the borehole enters the pore space under the effect of concentration difference, forming the gas diffusion phenomenon; following Fick's law of diffusion, the flow equation is The current research into gas flow within the fracture field of the coal body around the borehole belongs to the field of dual medium flow, where the pore and fracture structures around the borehole are considered as two separate permeable media [29]. The flow process can also be divided into three main stages:…”

Section: Theorymentioning

confidence: 99%

Experimental Investigation of the Fractal-Permeability Properties of Locally Fractured Coal Bodies around Gas Extraction Boreholes

et al. 2023

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To investigate the permeability characteristics in the in-situ fractured coal body around the perimeter of gas extraction boreholes, the steady-state permeability of fractured coal bodies with different gradations was tested using the fractured rock permeability test system. By controlling the axial displacement and permeability pressure, the permeability parameters were obtained under different porosities. The interactions between the permeability parameters and the process of permeability destabilisation are discussed. The results show that the permeability characteristics of the broken coal body obey the Forchheimer relationship: As the axial displacement increases, the permeability resistance of the fluid increases and the non-Darcy property of the sample becomes more significant. With the decrease in the porosity of the sample and the increase in the power index n, the permeability k decreases and the non-Darcy factor β increases. The final fractal structure of the sample will be changed by particle fragmentation and migration during the loading process of the sample with different levels, and the internal pore structure of the sample will further affect the penetration of the penetration channel. A critical characteristic value for the seepage instability in broken coal bodies is given, and an expression for determining the seepage instability by permeability and non-Darcy factors is proposed. The results indicate that a negative non-Darcy factor is not a necessary condition for permeability instability, and the critical Reynolds number for the permeability instability in broken coal bodies was determined from the perspective of the Reynolds number. The conclusions of this study can provide theoretical support for the theoretical study of permeability and the permeability of pre-smoking coal seams.

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Section: Theorymentioning

confidence: 99%

Experimental Investigation of the Fractal-Permeability Properties of Locally Fractured Coal Bodies around Gas Extraction Boreholes

et al. 2023

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“…Gas extraction ensures the safe mining of working faces and allows for the acquisition of gas resources, resulting in supplementary economic and social benefits for the mines. − High-gas mines are the primary target for gas extraction in our country, and data indicates that nearly 95% of the coal seams within these high-gas mines are soft . The characteristics of smooth coal seams, such as low strength coefficients and mechanical intensity, make them prone to accidents such as collapsing, drilling suction, roof drilling, blowouts, and stuck drilling, particularly under the weight of overlying rock strata in deeper areas. − These incidents, ranging from minor impacts on drilling efficiency, length, and extraction scope to severe cases of lost drilling directly, affects the progress of gas extraction work, restricting the safety and efficiency of the coal industry. − …”

Section: Introductionmentioning

confidence: 99%

Preferred Ratio and Properties of Microfoam Drilling Fluid for Gas Extraction in Soft Coal Seams

Cheng,

Hou,

Luo

et al. 2024

Energy Fuels

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During the gas extraction drilling process, especially the soft coal seam drilling process, due to the constraints of geological conditions, technical conditions, and other factors, it is easy to encounter stuck holes, blowout, lost circulation, and hole collapse, which affect the realization of efficient gas management. In the petroleum industry, microfoam drilling fluid has unique advantages as a drilling and flushing medium. Through the response surface method, this study conducts a preliminary experimental study on the types of foaming agents, foam stabilizers, modified bentonite materials, and filtrate reducers and determines the optimal formula as 3.98% modified bentonite + 0.586% compound foaming agent + 0.776% foam stabilizer + 1% sulfonated phenolic resin + 2% carboxymethyl starch sodium. The performance of the microfoam drilling fluid system is tested. Subsequently, a simulated soft coal seam drilling test is carried out to verify the effectiveness of the developed directional microfoam drilling fluid for protecting coal rock holes. This microfoam drilling fluid system technology can improve the drilling quality of the sealing section of coal seam gas extraction drilling and effectively improve the gas extraction rate of coal mines.

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“…Efficient extraction of gas energy from mines not only reduces gas disasters, but also plays an important role in improving China’s energy structure and helps to achieve the goal of "carbon neutrality" [ 1 , 2 ]. In recent years, China’s gas extraction and utilization technology has made progress, but there is still unbalanced extraction, and the overall low extraction concentration and extraction rate [ 3 , 4 ].…”

Section: Introductionmentioning

confidence: 99%

Ultrasonic characteristics and equivalent crack width of coal and rock bodies around boreholes during progressive failure

Zhang

et al. 2023

PLoS ONE

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The ultrasonic characteristics of the coal and rock bodies around boreholes during failure are closely related to the crack propagation law. To investigate the ultrasonic characteristics and crack propagation law of coal and rock bodies around boreholes, different grouting samples with boreholes were taken to carry out ultrasonic test during progressive failure. The ultrasonic amplitude, velocity and attenuation coefficient of the samples were analyzed. According to the ultrasonic time difference formula, the equivalent crack width of the sample during the failure process is calculated. The influence of grouting material on the crack propagation law is quantitatively analyzed. The results show that: (1) The peak stress, elastic energy at the peak, ultrasonic parameters and crack propagation of the coal and rock bodies around boreholes show obvious differences influenced by the strength of the grouting material. (2) During the loading process, the arrival time of the first wave of the sample with holes is 5μs later than that of the grouting sample, and the ultrasonic energy attenuates fastest in the time domain, and the coda wave is not developed. (3) During the progressive failure, the ultrasonic velocity and attenuation coefficient of all show three stages of stability(0~0.6σp), slow change(0.6σp~0.8σp) and rapid change(0.8σp~1.0σp). According to the "sudden decrease" of velocity and the "sudden increase" of attenuation coefficient to judge the crack propagation of sample. (4) The equivalent crack width of the sample increases exponentially with the increase of stress level. At the time of reaching the peak stress, the equivalent crack width of SH-BH increases about 0.027mm~0.032mm, SH-PU about 0.01mm~0.014mm, and SH-CEM about 0.002mm~0.006mm.

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Experimental investigation of flow regime transition characteristics of fractured coal bodies around gas extraction boreholes

Cited by 11 publications

References 22 publications

Experimental Investigation of the Fractal-Permeability Properties of Locally Fractured Coal Bodies around Gas Extraction Boreholes

Experimental Investigation of the Fractal-Permeability Properties of Locally Fractured Coal Bodies around Gas Extraction Boreholes

Preferred Ratio and Properties of Microfoam Drilling Fluid for Gas Extraction in Soft Coal Seams

Ultrasonic characteristics and equivalent crack width of coal and rock bodies around boreholes during progressive failure

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