| Summary: | In destressing and fracturing formation with multipulse gas loading, the pressure gradient of deflagration gas along cracks affects crack initiation and extension. The overlay principle is used to resolve complicated loads of the borehole wall into simple ones, based on elastic mechanics and linear elastic fracture mechanics. A function describing gas pressure distribution along the crack is proposed to derive the corresponding stress strength of the crack top, and then the conditions of crack initiation in borehole rocks are concluded. The conditions reflect the influence of the gas pressure gradient varying with time on fracture geometry. The example analysis and field contrast test reveal that, compared with the common High Energy Gas Fracturing, multipulse gas loading fracturing gives rise to higher crack initiation pressure, lower crack arrest pressure, greater extension of fracturing time, and forms twice to thrice the fracture length in the formation. Combined with hydraulic fracturing, it can lower formation breakdown pressure and further improve formation permeability. Key words: multipulse, load fracturing, deflagration gas, crack extension
|
|---|
