Journal
JOURNAL OF NATURAL GAS SCIENCE AND ENGINEERING
Volume 55, Issue -, Pages 382-394Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.jngse.2018.04.022
Keywords
Supercritical carbon dioxide; Shale; AE monitoring; CT scanning; Fracture
Categories
Funding
- National Program on Key Basic Research Project of China (973 Program) [2014CB239204]
- National Natural Science Foundation of China [51574049, 51774060]
- Program for Changjiang Scholars and Innovative Research Team in University [IRT_17R112]
- Major Natural Science Program for Central Universities [106112017CDJPT240001]
- Chongqing Frontiers and Application Foundation Research Program [cstc2015jcyjys90001, cstc2014jcyjA1189]
- Fundamental Research Funds for the Central Universities [106112016CDJZR245519]
- Chongqing Land Bureau Science and Technology Planning project [KJ-2015040]
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Supercritical carbon dioxide (SC-CO2) fracturing technique used in the development of shale gas has attracted increasing attention in the past decades. Using a self-developed physical simulation system equipped with acoustic emission (AE) and computed tomography (CT) system, the fracture initiation pressure (FIP) and fracture propagation mechanism of shale in the process of SC-CO(2 )fracturing was invested. The results show that the FIP for the shale without pre-existing fractures obtained from experiment is consistent with the theoretical values under different triaxial stress conditions, indicating that the theoretical calculation for FIP is feasible. The FIP increased gradually with increasing in situ stress for the shale without pre-existing fractures. The pre-existing fractures will affect the FIP and the fracture propagation direction in the shale. AE signals are obviously observed in the fracture initiation and the fracture propagation stages. In addition, the hit, energy, and amplitude are increased stepwise with increasing fracturing time. In the triaxial stress state, the initiation position and the propagation direction of cracks are random in the process of the SC-CO2 fracturing of shale and are along the direction of weak structural planes or pre-existing fractures. The SC-CO2 fracturing technique integrated with AE monitoring and CT scanning can be used to analyse the crack initiation position, the direction and sequence of crack propagation, and the number of the fracturing-generated cracks in shale. This research lays a foundation for SC-CO2 fracturing of shale in the Longmaxi formation in the Sichuan Basin.
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