Damage and fracture characteristics of coal-sandstone-shale under high pressure water jet impact

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Journal of Vibration and Shock ›› 2021, Vol. 40 ›› Issue (13) : 174-181.

GE Zhaolong1,2, ZHAO Hanyun1,2, LU Yiyu1,2, XIAO Songqiang1,2, ZHOU Zhe1,2, BO Tao3

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Abstract

High pressure water jet technology is widely used in field of resource exploitation as an efficient method to exploit oil and gas resources. Here, considering different destruction characteristics of unconventional oil and gas reservoir rock under impact of high-pressure water jet, taking representative coal, sandstone and shale as study objects, water jet rock breaking tests were conducted, and coal rock failure mode, morphology of micro-destruction and pore structure change were analyzed using the scanning electron microscope, CT and nuclear magnetic resonance technology. The results showed that under the same test parameters, failure characteristics of 3 kinds of rock body under high-pressure water jet impact are obviously different, coal body after erosion is dominated by longitudinal splitting due to water wedge leading action, sandstone is dominated by "spindle" fracture pits due to jet erosion leading action, and shale is dominated by shallow transverse annular cracks and bottom longitudinal splitting caused by stress wave and water wedge; damage degree of different depth sections of coal body fluctuates within 10%, only weak damage exists at fracture pits of sandstone, and serious damage exists in shallow part of shale, the maximum is up to 70%; macropores in coal body after erosion are 8 times of those before erosion, a large number of micro-pores in sandstone are changed into mesopores after erosion, and macropores in shale significantly increase, their number after erosion is about 300 times of that before erosion; for micro- fracture mechanism after erosion, there are traces of crystal fracture on coal body surface, rock bits on erosion surface of sandstone are greatly reduced and a large number of pores are left, traces of uniform crystal tensile fracture can be seen on erosion surface of shale; the study results can provide a theoretical guidance for using water jet to improve crushing efficiency of unconventional natural gas reservoir rock.

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high-pressure water jet / unconventional oil and gas reservoir / damage failure / micro-fracture / pore

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GE Zhaolong1,2, ZHAO Hanyun1,2, LU Yiyu1,2, XIAO Songqiang1,2, ZHOU Zhe1,2, BO Tao3. Damage and fracture characteristics of coal-sandstone-shale under high pressure water jet impact[J]. Journal of Vibration and Shock, 2021, 40(13): 174-181

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