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Energies 2017, 10(9), 1388; https://doi.org/10.3390/en10091388

A New Tree-Type Fracturing Method for Stimulating Coal Seam Gas Reservoirs

1,2
,
1,2,* , 1,2
,
1,2,* , 1,2
and
1,2
1
State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China
2
National & Local Joint Engineering Laboratory of Gas Drainage in Complex Coal Seam, Chongqing University, Chongqing 400044, China
*
Authors to whom correspondence should be addressed.
Received: 20 August 2017 / Revised: 3 September 2017 / Accepted: 8 September 2017 / Published: 13 September 2017
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Abstract

Hydraulic fracturing is used widely to stimulate coalbed methane production in coal mines. However, some factors associated with conventional hydraulic fracturing, such as the simple morphology of the fractures it generates and inhomogeneous stress relief, limit its scope of application in coal mines. These problems mean that gas extraction efficiency is low. Conventional fracturing may leave hidden pockets of gas, which will be safety hazards for subsequent coal mining operations. Based on a new drilling technique applicable to drilling boreholes in coal seams, this paper proposes a tree-type fracturing technique for stimulating reservoir volumes. Tree-type fracturing simulation experiments using a large-scale triaxial testing apparatus were conducted in the laboratory. In contrast to the single hole drilled for conventional hydraulic fracturing, the tree-type sub-boreholes induce radial and tangential fractures that form complex fracture networks. These fracture networks can eliminate the “blank area” that may host dangerous gas pockets. Gas seepage in tree-type fractures was analyzed, and gas seepage tests after tree-type fracturing showed that permeability was greatly enhanced. The equipment developed for tree-type fracturing was tested in the Fengchun underground coal mine in China. After implementing tree-type fracturing, the gas extraction rate was around 2.3 times greater than that for traditional fracturing, and the extraction rate remained high for a long time during a 30-day test. This shortened the gas drainage time and improved gas extraction efficiency. View Full-Text
Keywords: hydraulic fracturing; coal seam; stimulating reservoir volumes (SRV); triaxial testing; gas seepage hydraulic fracturing; coal seam; stimulating reservoir volumes (SRV); triaxial testing; gas seepage
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Li, Q.; Lu, Y.; Ge, Z.; Zhou, Z.; Zheng, J.; Xiao, S. A New Tree-Type Fracturing Method for Stimulating Coal Seam Gas Reservoirs. Energies 2017, 10, 1388.

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