Stress–Strain Modeling and Brittleness Variations of Low-Clay Shales with CO2/CO2-Water Imbibition
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A better understanding of the stress–strain behaviors of shale samples after shale-CO2 or shale-water–CO2 interactions is of great importance to CO2 enhanced shale gas exploitation and CO2 sequestrating in shale reservoirs. In this study, a constitutive model that combines with the modified Duncan–Chang model and Weibull distribution-based model is applied to investigate the stress–strain characteristics of low-clay shale samples treated by sub-/super-critical CO2 and sub-/super-critical CO2 + water for different times (10 days, 20 days, and 30 days). The results show that the model could describe well the crack closure stage, the elastic stage, and the inelastic stage of shale samples. The axial strain at the connection point between the two models varies from 28.51 to 43.36% of the axial strain at the failure point. Shale-CO2 or shale-water–CO2 interactions make shale samples more ductile at the crack closure stage, which can be depicted as the increase of initial elastic modulus during the imbibition process. The brittleness index values (BI) which are calculated based on the combined constitutive model increase with increasing soaking time for shale samples treated by sub-/super-critical CO2, and decrease with increasing soaking time for shale samples treated by sub-/super-critical CO2 + water.
KeywordsLow-clay shale CO2/CO2 + water imbibition Constitutive model Brittleness
The authors would like to thank all the technical staffs of the Geo-lab at Monash University for their help with the experimental work, the help of Prof. Jeffrey M. Dick and Dr. Asim Shahzad for the writing revision, and the financial support from the Innovation-Driven Project of Central South University (Grant no.: 502501005), the National Natural Science Foundation of China (Grant No. 41872151), and the China Postdoctoral Science Foundation (Grant no.: 2018M630913).
Compliance with ethical standards
Conflict of interest
On behalf of all authors, the corresponding author states that there is no conflict of interest.
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