Shrinkage of coal matrix with release of gas and its impact on permeability of coal

Harpalani, Satya; Schraufnagel, R.A.

doi:10.1016/0016-2361(90)90137-f

Cited by 372 publications

(140 citation statements)

References 2 publications

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“…These HM coupled processes can have important consequences during underground mining of coal (Liu andElsworth 1997, Xiao andXu, 2000) and during extraction of methane from coal seams. To recover a large percentage of methane gas in coalbeds, reservoir pressure must be reduced significantly (Harpalani and Schraufnagel 1990). Two distinct effects are associated with the reduction of pressure during methane extraction: (1) the release of gas and (2) an increase in effective stress.…”

Section: Coal Mining and Coal Methane Extractionmentioning

confidence: 99%

The role of hydromechanical coupling in fractured rock engineering

Rutqvist

Stephansson

2003

Hydrogeology Journal

575

332

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This paper provides a review of hydromechanical (HM) couplings in fractured rock, with special emphasis on HM interactions as a result of or directly connected with human activities. In the early 1960s, the coupling between hydraulic and mechanical processes in fractured rock started to receive wide attention. A series of events-including dam failures, landslides, and injection-induced earthquakes-were believed to result from HM interaction. Moreover, the advent of the computer technology in the 1970s made possible the integration of nonlinear processes such as stress-permeability coupling and rock mass failure into coupled HM analysis. Coupled HM analysis is currently being applied to many geological engineering practices. One key parameter in such analysis is a good estimate of the relationship between stress and permeability. Based on available laboratory and field data it was found that the permeability of fractured rock masses tends to be most sensitive to stress changes at shallow depth (low stress) and in areas of low in situ permeability. In highly permeable fractured rock sections, fluid flow may take place in clusters of connected fractures that are locked open as a result of previous shear dislocation or partial cementation of hard mineral filling. Such locked open fractures tend to be relatively insensitive to stress and may therefore be conductive at great depths.Because of out the great variability of HM properties in fractured rock, and the difficulties in using laboratory data for deriving in situ material properties, the HM properties of fractured rock masses are best characterized in situ.

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Section: Coal Mining and Coal Methane Extractionmentioning

confidence: 99%

The role of hydromechanical coupling in fractured rock engineering

Rutqvist

Stephansson

2003

Hydrogeology Journal

575

332

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“…Both effects will significantly affect coal permeability. Harpalani and Schraufnagel (1990) believed that coal permeability to methane increases with decreasing gas pressure despite increased effective stress. Zhu et al (2013) considered the coal-matrix damage induced by gas adsorption/desorption to explain the change in coal permeability under constant effective stress.…”

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confidence: 99%

Coal permeability model on the effect of gas extraction within effective influence zone

Xie

Gao

et al. 2015

Geomech. Geophys. Geo-energ. Geo-resour.

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In situ gas extraction is the main measure adopted by mines to achieve mining safety standards. Coal permeability is significantly influenced by coal shrinkage during gas release. Based on effective stress and additional damage that resulted from gas extraction, a unique model was proposed to describe the spatial and temporal distribution of coal permeability within the effective influence zone. Calculation models for the conditions of one and two extracting boreholes were developed. A parametric study on both two models was also conducted, in which the effect of extraction time, extraction pressure, interval between two boreholes, and extraction pressure combination were qualitatively analyzed. The results demonstrated that with the increase of extraction time, gas extraction can result in less permeability reduction in the beginning but can enhance permeability. Coal permeability obviously increases when extraction time increases but gradually stabilizes, presenting ''high middle and low around'' surrounding the extracting borehole. Meanwhile, a decreasing relative amplification implies that permeability ratio does not increase linearly with the increase in extraction pressure. Both intervals between two extracting boreholes and different combinations of extraction pressure significantly influence the distribution of coal permeability. A comparison with some previous permeability studies was conducted to validate the proposed model, and the predicted evolution results matched the permeability testing data. In conclusion, the proposed model is consistent with the phenomenon in real engineering, and the model results can provide preliminary guidance for the design of extracting borehole distribution.

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“…Cleats contribute to permeability by providing migration pathways for gas and water flow to the well. The CBM gas is produced by diffusion from the coal matrix and Darcy flow through the cleat system [4], until it reaches the production well. Since cleats are responsible for the majority of fluid flow to the producing gas, they are considered to be one of the most important parameters that determine the permeability of CBM reservoirs.…”

Section: Introductionmentioning

confidence: 99%

Tectonics and Geological Factors Controlling Cleat Development in the Barito Basin, Indonesia

Sapiie

Rifiyanto

2017

J. Eng. Technol. Sci.

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Abstract. Cleats are natural fractures within coal seams. This paper presents the results of regional cleat mapping and characterization in relation to coalbed methane (CBM) exploration and development in the Barito Basin, South Kalimantan, Indonesia involving two major coal layers, namely the Late Eocene Tanjung Formation and Early to Middle Miocene Warukin Formation with thicknesses ranging from 2 to 50 m. The coal is classified as lignite to subbituminous with calorific values ranging from 6000-8000 Cal/gr with ash content 0.68-17.42%. We applied two methods of cleat measurement, i.e. scanline and window sampling using a 100 x 100 cm grid. More than 20,000 cleats were measured from 65 scanline and 37 window sampling locations. The results revealed that face and butt cleats are predominantly oriented in the WNW-ESE and NNE-SSW directions, respectively. The results showed that cleat density increases related to structural position such as fold hinge and fault zone. The formation of the cleats may be influenced by several geological processes, where the cleats, which form during coalification, are superimposed by later processes such as fluid pressure and tectonic stresses and are seemingly also affected by the composition of the coal.

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Shrinkage of coal matrix with release of gas and its impact on permeability of coal

Cited by 372 publications

References 2 publications

The role of hydromechanical coupling in fractured rock engineering

The role of hydromechanical coupling in fractured rock engineering

Coal permeability model on the effect of gas extraction within effective influence zone

Tectonics and Geological Factors Controlling Cleat Development in the Barito Basin, Indonesia

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