Abstract
In this paper, whether the coal fines can be induced by shear failure during drainage process has been discussed in detail. By coupling with the percolation theory, the elasticity mechanics were used to construe the extra stresses in the formation surrounding with the hydraulic fracture. The safe window of the bottom hole pressure was also calculated from the failure envelope. The research shows that the formation pressure on the fracture surface of the coal seam is negatively related with the bottom hole pressure, and the induced stress is positively related with the bottom hole pressure during the drainage process of fractured CBM wells. The pore pressure around the fracture changed due to pore-elastic effects, which also caused a significant change of the in situ stresses. In order to avoid the breakout of the coal seam around hydraulic fracture during drainage process, the model of the reasonable bottom hole pressure is also built.
Highlights
IntroductionThe coalbed methane (CBM) resources in China are abundant, and the exploration and development of CBM in China have made great achievements; what is more, the CBM has achieved commercial exploitation and development
The coalbed methane (CBM) resources in China are abundant, and the exploration and development of CBM in China have made great achievements; what is more, the CBM has achieved commercial exploitation and development.During the operation of CBM wells, coal fines are generated due to the rise of liquid level or pressure changes (Liu et al 2012a, b; Zhang et al 2009)
The conclusion can be made that the formation pressure on the fracture surface of the coal seam is negatively related with the bottom hole pressure, and the induced stress is positively related with the bottom hole pressure
Summary
The coalbed methane (CBM) resources in China are abundant, and the exploration and development of CBM in China have made great achievements; what is more, the CBM has achieved commercial exploitation and development. During the operation of CBM wells, coal fines are generated due to the rise of liquid level or pressure changes (Liu et al 2012a, b; Zhang et al 2009). Wei et al (2013) points out that coal fines production results from unreasonable drainage operation parameters, such as unreasonable bottom hole pressure and drainage quantity (Wei et al 2013). Hydraulic fracturing can produce induced stress and result in the formation pressure declination in the coal seam, which leads to the redistribution of the in situ stress field near the fractures. The stability of fractures surface can be evaluated by the instability criterion, which is good to determine reasonable bottom hole pressure and hinders coal fines production
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