Experimental study on hydraulic fracture geometry of shale

For thorough understanding of the propagation and spatial form of hydraulic fracture of shale formations, a large-scale physical simulation test method for hydraulic fracture of shale is established by means of the large real triaxial simulation experiment system, servo control system of hydraulic fracturing, acoustic emission (AE) source orientation technique and CT scanning technology. The mechanism of the formation of the fracture network is exposed according to the crack extension and special distribution of shale tested by this method. The results indicate that the typical jagged pump pressure-time curve at extending stage, which may be closely related to the formation of fracture network, is an obvious feature of the volume fracture of shale. The fracture morphology is strongly influenced by the development degree of bedding planes, pump pressures and stress conditions. Branching and re-orientation of hydraulic fractures in bedding planes and then interconnecting with natural fractures are the main factors of the formation of fracture network. The bedding plane which is too weak or too strong is not conducive to the formation of fracture mesh. The stress condition plays a great role in controlling the extension of fractures for intermediate formations. Hydraulic fractures are easy to change direction and propagate when the pump pressure is kept at a lower level. The physical simulation method for hydraulic fracture and the corresponding test results can provide references for fracture optimization design in exploiting shale gas.