Research on Evolutionary Laws of Mechanical Properties and Pore Structure during CO 2 Pre-Injection Fracturing in Shale Reservoirs

Jiaping Tao, Siwei Meng (), Dongxu Li, Xu Jin, Lihao Liang and He Liu
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Jiaping Tao: PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China
Siwei Meng: PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China
Dongxu Li: PetroChina Daqing Oilfield Co., Ltd., Daqing 163002, China
Xu Jin: PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China
Lihao Liang: PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China
He Liu: PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China

Energies, 2024, vol. 17, issue 11, 1-15

Abstract: CO 2 pre-injection fracturing is a promising technology for shale reservoirs development, with multiple advantages for improving the complexity of fractures, the production of crude oil, and the sequestration of CO 2 . Previous research mostly focused on the CO 2 effect on macroscopic mechanical properties of shale. However, there are many phenomena closely related to shale micro mechanical behavior. Therefore, this study presents a systematic investigation into the effects of CO 2 on both macro and micro mechanical properties, as well as pore-fracture structures during CO 2 pre-injection fracturing in shale reservoirs. The results show that CO 2 can significantly decrease the tensile strength, uniaxial compressive strength, and elastic modulus of shale. With the increasing CO 2 treatment time, the macro mechanical properties of shale decrease gradually. The microscopic experiments show that this significant decrease may be due to two mechanisms. The first is the significant decrease in the micro-mechanical properties of shale. The results of indentation analysis show that the microscopic elastic modulus and hardness of shale decrease by 51.3% and 63.3% after CO 2 treatment. The second is the changes of the original shale framework. Pore-fractures structure analysis showed that after CO 2 treatment, a large number of dissolution pores are generated in the shale matrix. Meanwhile, there are propagation of original fractures and opening of structural weak planes, which lead to the form of new fractures. Under the action of these two mechanisms, the macro mechanical strength of shale is reduced significantly. Therefore, in the field application, proper soaking following CO 2 injection could lead to a significant overall reduction in mechanical strength, potentially lowering formation breakdown pressure, easing the requirements for treatment equipment, and enhancing fracturing effects.

Keywords: shale formation; CO 2 treatment; indentation; micro-morphology; pore and micro-fracture (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: 2024
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