A New Tree-Type Fracturing Method for Stimulating Coal Seam Gas Reservoirs
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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.Keywords:
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Coalbed Methane
As the hunt for important unconventional gas resources in America expands, an increasingly popular method of wringing resources from stubborn underground formations is a process called hydraulic fracturing – also described as hydrofracturing, fracking, or fracing – wherein fluids are pumped at high pressure underground to fracture a formation and release trapped oil or gas. Operators have fraced wells for more than fifty years, but the practice has recently grown rapidly in areas like the Barnett Shale of North Central Texas and the Marcellus Shale beneath Pennsylvania, New York, and other Appalachian states. This Article describes the process of hydraulic fracturing, existing studies of the environmental effects of hydraulic fracturing, and the laws and regulations that apply to the practice. It argues that there is no direct federal regulation of the fracing process (the pumping of fluids into a wellbore), that court guidance in this area is limited, and that state regulations differ substantially. Although other general regulations apply to the practice, the Article argues that in light of the dearth of regulation specific to fracturing in some areas, more study of the potential environmental and human health effects of fracing is needed in order to determine whether current regulation is sufficient. The EPA completed a partial study in 2004, but this Article focuses on the deficiencies of that study and calls for a new, national, scientific study of the practice.
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As the hunt for important unconventional gas resources in America expands, an increasingly popular method of wringing resources from stubborn underground formations is a process called hydraulic fracturing – also described as hydrofracturing, fracking, or fracing – wherein fluids are pumped at high pressure underground to fracture a formation and release trapped oil or gas. Operators have fraced wells for more than fifty years, but the practice has recently grown rapidly in areas like the Barnett Shale of North Central Texas and the Marcellus Shale beneath Pennsylvania, New York, and other Appalachian states. This Article describes the process of hydraulic fracturing, existing studies of the environmental effects of hydraulic fracturing, and the laws and regulations that apply to the practice. It argues that there is no direct federal regulation of the fracing process (the pumping of fluids into a wellbore), that court guidance in this area is limited, and that state regulations differ substantially. Although other general regulations apply to the practice, the Article argues that in light of the dearth of regulation specific to fracturing in some areas, more study of the potential environmental and human health effects of fracing is needed in order to determine whether current regulation is sufficient. The EPA completed a partial study in 2004, but this Article focuses on the deficiencies of that study and calls for a new, national, scientific study of the practice.
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