Abstract
Low permeability of coalbed has always been a main bottleneck impeding the safety production of coal mines and the high-efficient gas recovery. A static fracturing technology, relied on hydraulic-driving modules to expand outwards for producing artificial fissures in coalbed, is proposed here for coalbed reservoir stimulation. The mechanical model of borehole fracturing is established to clarify the associated mechanisms for fracturing stimulation based on the elastic-plastic mechanics. The numerical results indicate when the fracturing load is over twice as much as in situ stress, the concentration of hoop stress around borehole would be released and the range of fracturing-induced fissures gradually extends with the rising load. While the lateral stress coefficient of strata rising from 1 to 3, the stress distribution around borehole evolves from a ring to a saddle shape, resulting in the horizontal extension of fissures in the early stage. According to underground monitoring, a significant improvement of coalbed permeability up to 5 times has been achieved in 16031 tailgate, in Guhanshan coalmine, China.
Highlights
On account of a specific energy structure and a gigantic consumption, China has already been the world’s largest coal producer with the output of 3.41 billion tons in 2016, suffering serious gas disasters [1, 2]
Many analytical models [10,11,12,13,14] were proposed to describe the dynamic changes in coalbed permeability during gas drainage period under uniaxial compression conditions. ese models show coal permeability reduces with the increase of in situ stress, representing a negative exponential function as the coalbed buried depth
A static fracturing technology to enhance the permeability of coalbed is proposed here for the high e ciency of gas recovery. e mechanism of borehole fracturing is clari ed based on the mechanical analysis and numerical modeling. e results demonstrate the following (1) When the fracturing load is over twice as much as in situ stress, the concentration of hoop stress around borehole is released and there are more tensile ssures generated with a rising load, which results in the promotion in coal permeability
Summary
On account of a specific energy structure and a gigantic consumption, China has already been the world’s largest coal producer with the output of 3.41 billion tons in 2016, suffering serious gas disasters [1, 2]. Many analytical models [10,11,12,13,14] were proposed to describe the dynamic changes in coalbed permeability during gas drainage period under uniaxial compression conditions. Ese models show coal permeability reduces with the increase of in situ stress, representing a negative exponential function as the coalbed buried depth. The existing permeability models, on the assumptions of uniaxial strain and constant vertical stress, have not taken into account the original stress state and the varying of cleat
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