Abstract：In order to analyze damage evolution state of coal sample in hydraulic fracture process，a joint test method combining borehole strain and electrical resistivity has been proposed. The borehole strain and electrical resistivity response characteristic of coal samples in hydraulic fracture process have been studied with self-developed hydraulic fracture experimental system. The curves of borehole strain，electrical resistivity and water pressure have been obtained while the response mechanism is analyzed. The results show that there is strong regularity in borehole strain and electrical resistivity curves. The borehole strain curves show “V” shape while the electrical resistivity curves show “” shape. When water takes up the space of borehole，the electrical resistivity of coal samples reaches the minimum value. When the borehole fractured，borehole strain and electrical resistivity increase to the maximum value gradually. Borehole strain reflects the deformation characteristic of borehole during hydraulic fracture process while the electrical resistivity reflects the initiation and development of fissure inner coal samples. Volume fracturing of coal samples causes the dilatation of fissure，resulting in sudden change of electrical resistivity. The curves of borehole strain，electrical resistivity and water pressure have rich information for fracturing of coal sample in hydraulic fracture process. And it provides a new method to analyze initiation behavior of coal sample in hydraulic fracture process.
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2016, Vol. 35 
