Effect of Hydration under High Temperature and Pressure on the Stress Thresholds of Shale

Jianfa Wu, Yintong Guo, Haoyong Huang (), Guokai Zhao, Qiyong Gou, Junchuan Gui and Ersi Xu
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Jianfa Wu: Shale Gas Research Institute of PetroChina Southwest Oil & Gas Field Company, Chengdu 610051, China
Yintong Guo: State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China
Haoyong Huang: Shale Gas Research Institute of PetroChina Southwest Oil & Gas Field Company, Chengdu 610051, China
Guokai Zhao: State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China
Qiyong Gou: Shale Gas Research Institute of PetroChina Southwest Oil & Gas Field Company, Chengdu 610051, China
Junchuan Gui: Shale Gas Research Institute of PetroChina Southwest Oil & Gas Field Company, Chengdu 610051, China
Ersi Xu: Shale Gas Research Institute of PetroChina Southwest Oil & Gas Field Company, Chengdu 610051, China

Energies, 2023, vol. 16, issue 23, 1-13

Abstract: The stress threshold of deep reservoir shale subjected to fracturing fluid immersion is an important factor affecting fracture initiation and propagation during fracturing. However, little information has been reported on the effect on shale of soaking at high temperature and high pressure (HTHP). In this study, immersion tests and triaxial compression tests were carried out at reservoir temperature and in-situ stress on the downhole cores with different mineral compositions. The characteristics of stress thresholds, i.e., crack initiation stress ( σ c i ), crack damage stress ( σ cd ), and peak deviator stress ( σ p ), of shale affected by the different times of soaking with low-viscosity fracturing fluid (a) and the different viscosity fracturing fluids (a, b, and c) were investigated. The results show that hydration at HTHP has a significant softening effect on the stress thresholds ( σ c i , σ cd , σ p ) of reservoir shale, but the softening rate varies for samples with different mineral compositions. The crack initiation stresses of quartz-rich and clay-rich shales treated with different soaking times and different soaking media remain almost unchanged in the range of 47 to 54% of the corresponding peak strength, while the crack initiation stresses of carbonate-rich shales are significantly affected. The ratio σ cd / σ p of quartz-rich shale is significantly affected by the different viscosity fracturing fluids (a, b) and the different times of soaking with low-viscosity fracturing fluid (a), while clay- and carbonate-rich shales are less affected. The results of this study can provide a reference for the fracturing design of deep shale gas development.

Keywords: shale; stress thresholds; fracturing fluid; high temperature and pressure (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
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