Calculation method for crack initiation pressure of shale formation fracturing crack

Abstract

The invention relates to a calculation method for the crack initiation pressure of a shale formation fracture crack. The calculation method specifically comprises the steps that 1, the magnitude of ground stress, the pore pressure of formation and the elastic modulus and Poisson ratio in different directions of a shale are tested; 2, a certain well depth value is selected for a layer section of atarget well, and a borehole rectangular coordinate system, a ground stress coordinate system and a geodetic coordinate system are converted according to designed wellbore structure data that; 3, stress components of the borehole wall caused by the ground stress and the fracturing fluid pressure in a wellbore are calculated; 4, the effective stress of the stress components on the borehole wall in the borehole rectangular coordinate system is converted into a effective stress form under polar coordinates of the wellbore; 5, a mechanical criterion of a tensile fracture of a rock of the fracturingwall of the shale formation is derived; and 6, the fracturing fluid pressure in the layer section wellbore of the target well is calculated along the circumferential direction of the wellbore when tensile fractures are generated at different positions of the borehole wall, and the minimum value of the fracture is determined as the crack initiation pressure. The calculation method for the crack initiation pressure of the shale formation fracture crack enables the calculation result of the crack initiation pressure more realistic and reliable, and reduces the construction cost.

Description

technical field [0001] The invention relates to shale formation fracturing reconstruction technology, in particular to a method for calculating the initiation pressure of shale formation fracturing cracks. Background technique [0002] Shale gas has been regarded as an important sustainable energy alternative to coal and conventional oil and natural gas. The total global resources of shale gas are about 4.56×10 14 m 3 , accounting for about 50% of the world's unconventional oil and gas resources, equivalent to 1.4 times of conventional natural gas, has been recognized as an important energy source that changes the world's energy pattern and enables global oil and gas exploration to show good development prospects. [0003] According to statistics, there are about 600×10 natural gas supply in my country in 2015 8 m 3 The left and right gap needs to be imported, and it is estimated that by 2020, the domestic natural gas gap will reach 1000×10 8 m 3 . If shale gas resour...

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Problems solved by technology

[0010] The purpose of the present invention is to provide a method for calculating the initiation pressure of fracturing fractures in shale fo

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