Phenomenon of methane driven caused by hydraulic fracturing in methane-bearing coal seams

Huang, Bingxiang; Cheng, Qingying; Chen, Shuliang

doi:10.1016/j.ijmst.2016.05.042

Cited by 36 publications

(24 citation statements)

References 15 publications

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“…This is because after water enters the coal, both the free methane in the pores and the free methane from the adsorbed methane displaced by water are driven out at the same time. Although only a small volume of the methane is displaced by water, its existence is confirmed by the experiment [1,[32][33][34][35]. Currently, the methane displaced by water cannot be quantitatively calculated by the mathematical formula.…”

Section: Comparisons Of the Experiments And Numericalmentioning

confidence: 93%

“…During the process of water injection or hydraulic fracturing in gassy coal, the methane concentration of the airflow in the roadway clearly increases. This phenomenon is known as the water-driven-methane effect [1]. The existence of this phenomenon has been shown in laboratory experiments.…”

Section: Introductionmentioning

confidence: 90%

“…The water drives the methane in the pore to move forward in the pore channel until the methane is expelled from the coal rock mass. At the same time, the pore space of methane is also occupied by water [1]. The pore space occupied by water forms the water zone, but a certain amount of methane remains in the water zone.…”

Section: Geofluidsmentioning

confidence: 99%

“…A coupled fluid-solid mathematical model that considers the effects of methane adsorption and desorption has already been established to describe this stage, but it still cannot be directly used to describe the water-driven-methane process in coal because of the following reasons. (1) The coupled fluid-solid model of coalbed methane drainage is used to describe the process of water-methane two-phase flow with a decrease in the water pressure and adsorbed coalbed methane becoming free coalbed methane. However, a coupled fluid-solid model of methane driven by water is required to describe the process of driving out methane in coal by the injected water, which is injected into the coal.…”

Section: Introductionmentioning

confidence: 99%

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A Fluid-Solid Coupling Mathematical Model of Methane Driven by Water in Porous Coal

Huang

2018

Geofluids

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The existence of the water-driven-methane effect in gassy coal has been verified by field tests and laboratory experiments. However, a water-driven-methane mathematical model that considers methane adsorption and desorption has not yet been established. Based on the water-driven-methane process, a fluid-solid coupling mathematical model of methane driven by water is established. The model’s reliability is verified by the results of a water-driven-methane physical experiment and by using a solution of the COMSOL Multiphysics software. The space-time distribution regularities of the pore pressure, water-methane two-phase saturation, and pore pressure gradient in the water-driven-methane process are analysed. The results reveal the following. (1) The water-driven-methane fluid-solid coupling mathematical model for porous coal is reliable. (2) In the water-driven-methane process, there is an increasing zone and a decreasing zone of pore pressure in the coal sample. The increasing zone of pore pressure is closest to the side of the water inlet, and its area gradually decreases. The decreasing zone of pore pressure is closest to the side of the methane outlet, and its area gradually increases. Over time, the methane pressure in the increasing zone of pore pressure first increases and then decreases, and the methane pressure in the decreasing zone of pore pressure continuously decreases. The change (increase or decrease) rate of the methane pressure gradually decreases from both ends towards the middle of the coal sample. (3) The curve of the water saturation over time changes from a lower concave curve to a straight line, while the curve of the methane saturation with time changes from an upper convex curve to a straight line. The methane saturation in the decreasing zone of pore pressure is greater than that in the increasing zone of pore pressure. Over time, the water saturation of a specific point in space continuously increases while its methane saturation continuously decreases. Both of the increase rate of the water saturation and the decrease rate of the methane saturation gradually reduce over time. (4) The pore pressure gradient along the driving direction first decreases and then increases. The decreasing zone of the pore pressure gradient is located in the increasing zone of pore pressure, and the increasing zone of the pore pressure gradient is located in the decreasing zone of pore pressure. Over time, the pore pressure gradient at the side of the water inlet increases, and its increase rate decreases. The pore pressure gradient at the side of the methane outlet decreases, and its decrease rate decreases. The rate of increase in the pore pressure gradient at the side of the water inlet is greater than the rate of decrease in the pore pressure gradient at the side of the methane outlet.

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Section: Comparisons Of the Experiments And Numericalmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 90%

Section: Geofluidsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Fluid-Solid Coupling Mathematical Model of Methane Driven by Water in Porous Coal

Huang

2018

Geofluids

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“…Longwall gob is composed of fractured and caved (or crushed) rocks and compressed by overburden load [1][2][3]. Considering the importance of caved rocks in longwall gob, they have been researched and applied in many respects, including inferring the position of main roof and overburden structure [4][5][6], estimating the pressure and permeability distribution of gob [7,8], and evaluating feasibilities of mining in methane relieving seam [9].…”

Section: Introductionmentioning

confidence: 99%

Experimental Research on Internal Behaviors of Caved Rocks under the Uniaxial Confined Compression

Zhāng¹,

Feng²,

Qi³

2017

Advances in Materials Science and Engineering

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As main composition of longwall gob, caved rocks’ behaviors and their impacts under compression crucially influence strata control, subsidence, associated resources extraction, and many other aspects. However, current researches are based on a whole sample, due to looseness of caved rocks and limitation of observation technology. In this paper, an experiment system was built to investigate internal behaviors of caved rocks’ sample, under the uniaxial confined compression, including movement and breakage behavior by the digital image processing technologies. The results show that the compression process of caved rocks could be divided into two stages by relative density. Boundary effect and changes of voids and contact pressure among caved rocks lead to different movement law in different position in sample’s interior. A stratification phenomenon of breakage was discovered, which presents breakage concentration in the middle of the sample. The nonlinear movement and shear dislocation induced by shifts among caved rocks are the reason of the breakage stratification phenomenon. This phenomenon would have an effect on the permeability and seepage research of similar medium.

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Analysis of the tempo‐spatial effects of hydraulic fracturing by drilling through underground coal mine strata on desorption characteristics

Bai

2018

Energy Science & Engineering

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To elucidate the tempo‐spatial effect and the corresponding mechanism of hydraulic fracturing on gas desorption, the experiments of the hydraulic fracturing in the field and the gas adsorption‐desorption in the laboratory were carried out, respectively. The difference of the effects on the total amount of gas desorption, desorption proportion, moisture content, and in situ gas drainage concentration of the original and fracturing coal samples were studied. The results show that coal moisture increase in the 29 m area of hydraulic fracturing, the greater moisture content and the smaller amount of gas desorption, and the 9 m coal samples moisture content is 2.77 times greater than that of the original coal samples, and whose total amount of gas desorption for 29.8% of the original coal samples. In addition, the closer to the fracturing borehole, the smaller the desorption velocity, which is the fastest in the initial 5 minutes. The desorption velocity of the original coal samples is 5.6 times greater than that of the 9 m coal samples. The desorption proportion of the coal samples is high in early stages, η30 min is 64% (ηi is the proportion of the instantaneous total of gas desorption to the total gas desorption, %), and for η6 h‐12 h is 10%. The tempo‐spatial effects of desorption characteristics can be expressed as the time‐delay effect and a space‐reduction effect. Furthermore, the upper limit of deformation of the coal seam is 3.3‰ and the ability of gas desorption in coal seam significantly decreases. The time of gas drainage concentration exhibits more than 30% increases from the 10 days in the nonfracturing area to 90 days in the fracturing area. Finally, hydraulic fracturing crushes coal, replaces absorption gas, increases the moisture content of coal, reduces various stresses, makes coal shrink, and ultimately achieves the effects of pressure relief and permeability improvement.

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Phenomenon of methane driven caused by hydraulic fracturing in methane-bearing coal seams

Cited by 36 publications

References 15 publications

A Fluid-Solid Coupling Mathematical Model of Methane Driven by Water in Porous Coal

A Fluid-Solid Coupling Mathematical Model of Methane Driven by Water in Porous Coal

Experimental Research on Internal Behaviors of Caved Rocks under the Uniaxial Confined Compression

Analysis of the tempo‐spatial effects of hydraulic fracturing by drilling through underground coal mine strata on desorption characteristics

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