Method for designing safety drilling fluid density window during shale formation drilling

Abstract

The invention relates to a method for designing a safety drilling fluid density window during shale formation drilling. The method specifically comprises the following steps: testing crustal stress, formation pore pressure and the like; transforming a borehole rectangular coordinate system, a geostress coordinate system and a geodetic coordinate system; calculating each stress component of the well walls caused by geostress and drilling fluid pressure in the borehole; transforming effective stress of each stress component on the well walls in the borehole rectangular coordinate system into aneffective stress form in a borehole polar coordinate system; deducing mechanical laws of tensile and compressive shear failure occurring in wall rock during shale drilling, namely calculating the pressure of drilling fluid in the borehole when tensile and compressive shear failure occurs at different positions of the wall along the circumferential direction of the borehole, and respectively determining the converted drilling fluid density corresponding to the fracture pressure and collapse pressure; summarizing the converted drilling fluid density corresponding to the fracture pressure and collapse pressure at all well depths on the interval of interest of a target well, and drawing the safety drilling fluid density window. According to the method disclosed by the invention, the design result of the safety drilling fluid density window is true and reliable.

Description

technical field [0001] The invention relates to a wellbore stability evaluation technology for drilling in shale formations, in particular to a method for designing a safe drilling fluid density window for drilling in shale formations. 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 ...

AI Technical Summary

Problems solved by technology

[0010] The object of the present invention is to provide a method for designing a safe drilling fluid density window for drilling in shale formations. This method for designing a safe drilling fluid density window for drilling in shale formations is used to solve the well wall rupture of the upper and lower limits of drilling fluid density in shale formation drilling. Pressure and collapse pressure calculation issues

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