TY - JOUR

T1 - Influence of cyclic normal stress on shear friction of EGS granite fractures

AU - Sheng, Mao

AU - Li, Pu

AU - Zhuang, Xiaoying

AU - Wang, Jianbo

N1 - Funding Information: This work was financially supported by the National Natural Science Foundation of China (Nos. 51704308 & 51911530239 ). We thank Professor Quan Xu for his valuable discussion and Mr. Tianwen Jiang, Mr. Waleed Ali Khan, and Mr. Panpan Zhang for their helpful assistants of testing.

PY - 2020/8/15

Y1 - 2020/8/15

N2 - Cyclic hydraulic fracturing has been proved to be an effective stimulation technique to explore EGS resouces. The shear friction behaviors under cyclic normal stress are essential to understand the hydro-shearing mechanisms. This paper proposed a cyclic shear friction test to understand the friction characteristics of granite fracture during cyclic hydraulic fracturing. A cyclic normal force in sinusoidal function and a constant shear velocity were enforced on the rock specimen. The time-dependent friction behaviors were observed. Results indicate that the frictional coefficient is highly correlated with the variation of the normal force. Futhermore, the frequency dependency of cyclic shear friction was observed. High-frequency normal force motivates a lower frictional shear slip. However, the amplitude of normal force displays an irregular influence on the frictional coefficient. Microstructure analysis demonstrated that numerous scratches and a powder-lubrication layer were generated along the sheared asperity between the fracture surfaces. High-frequency shear friction accelerates jumping shear and creates finer powder to lubricate the shear slip. The present work is helpful to understand the mechanisms of cyclic hydraulic fracturing to activiate the existing natural fractures.

AB - Cyclic hydraulic fracturing has been proved to be an effective stimulation technique to explore EGS resouces. The shear friction behaviors under cyclic normal stress are essential to understand the hydro-shearing mechanisms. This paper proposed a cyclic shear friction test to understand the friction characteristics of granite fracture during cyclic hydraulic fracturing. A cyclic normal force in sinusoidal function and a constant shear velocity were enforced on the rock specimen. The time-dependent friction behaviors were observed. Results indicate that the frictional coefficient is highly correlated with the variation of the normal force. Futhermore, the frequency dependency of cyclic shear friction was observed. High-frequency normal force motivates a lower frictional shear slip. However, the amplitude of normal force displays an irregular influence on the frictional coefficient. Microstructure analysis demonstrated that numerous scratches and a powder-lubrication layer were generated along the sheared asperity between the fracture surfaces. High-frequency shear friction accelerates jumping shear and creates finer powder to lubricate the shear slip. The present work is helpful to understand the mechanisms of cyclic hydraulic fracturing to activiate the existing natural fractures.

KW - Cyclic loading

KW - Granite fracture

KW - Jumping shear

KW - Powder lubrication

KW - Rock friction

UR - http://www.scopus.com/inward/record.url?scp=85089507315&partnerID=8YFLogxK

U2 - 10.1016/j.engfracmech.2020.107268

DO - 10.1016/j.engfracmech.2020.107268

M3 - Article

AN - SCOPUS:85089507315

VL - 238

JO - Engineering fracture mechanics

JF - Engineering fracture mechanics

SN - 0013-7944

M1 - 107268

ER -