Abstract
Due to the advantages of good fracture performance and the application of carbon capture and storage (CCS), supercritical carbon dioxide (SC-CO2) is considered a promising alternative for hydraulic fracturing. However, the fracture initiation mechanism and its propagation under pressurized SC-CO2 jet are still unknown. To address these problems, a fluid–structure interaction (FSI)-based numerical simulation model along with a user-defined code was used to investigate the fracture initiation in an inhomogeneous shale rock. The mechanism of fracturing under the effect of SC-CO2 jet was explored, and the effects of various influencing factors were analyzed and discussed. The results indicated that higher velocity jets of SC-CO2 not only caused hydraulic-fracturing ring, but also resulted in the increase of stress in the shale rock. It was found that, with the increase of perforation pressure, more cracks initiated at the tip. In contrast, the length of cracks at the root decreased. The length-to-diameter ratio and the aperture ratio distinctly affected the pressurization of SC-CO2 jet, and contributed to the non-linear distribution and various maximum values of the stress in shale rock. The results proved that Weibull probability distribution was appropriate for analysis of the fracture initiation. The studied parameters explain the distribution of weak elements, and they affect the stress field in shale rock.
Highlights
Due to its clean nature, shale gas has become the focus of research and development in the field of energy sciences
The SC-CO2 hydro-jet fracturing is regarded as a unique, cost-effective and efficient well-stimulation treatment owing to its capability to accomplish a multi-stage pin-point fracturing without the use of mechanical packers
Flow Field and Stress Filed before Fracture Initiation
Summary
Due to its clean nature, shale gas has become the focus of research and development in the field of energy sciences. Hydraulic fracture is an efficient method for commercial extraction of hydrocarbons in shale and tight reservoirs and has contributed to the boom of shale gas in the United States [1,2]. In order to reduce water consumption and CO2 emissions, SC-CO2 fracturing is regarded as a potential futuristic technology [3]. Compared to the conventional hydraulic fracturing technology, shale gas has several advantages, including low viscosity, small damage to the reservoir, outstanding permeability in fine pores and micro-cracks of shale. The SC-CO2 hydro-jet fracturing is regarded as a unique, cost-effective and efficient well-stimulation treatment owing to its capability to accomplish a multi-stage pin-point fracturing without the use of mechanical packers. The fracturing is accomplished due to the jet pressurization effect, while SC-CO2
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