Propagation Characteristics of Supercritical Carbon Dioxide Induced Fractures under True Tri-Axial Stresses

Yi Hu,Jiawei Liu,Yong Kang,Feng Liu,Hao Chen,Yuqiang Hu

doi:10.3390/en12224229

Yi Hu, Jiawei Liu + Show 4 more

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https://doi.org/10.3390/en12224229

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Abstract

Supercritical carbon dioxide (SC-CO2) fracturing is a non-aqueous fracturing technology, which has attracted considerable attention on exploiting shale gas. In this study, shale specimens and artificial sandstone specimens were used to conduct SC-CO2 fracturing and water fracturing experiments to investigate the characteristics of SC-CO2 induced fractures. An acoustic emission (AE) monitoring device was employed to monitor the AE energy release rate during the experiment. The experiment results indicate that the breakdown pressure of SC-CO2 fracturing is lower than that of water fracturing under the same conditions, and the AE energy release rate of SC-CO2 fracturing is 1–2 orders of magnitude higher than that of water fracturing. In artificial sandstone, which is homogeneous, the main fracture mainly propagates along the directions perpendicular to the minimum principal stress, no matter if using SC-CO2 or water as the fracturing fluid, but in shale with weak structural planes, the propagation direction of the fracture is controlled by the combined effect of a weak structural plane and in-situ stress.

Highlights

Shale gas is one of the unconventional resources which is stored in organic matter-rich shale formations
5a, theofartificial sandstone fractured by initiated from the open hole section and extended along directions approximately perpendicular to had a main fracture with multi-fracture branches, and the main fracture initiated from the open the minimum principal stress (σ h), connecting with a fracture propagated along the joint plane and a hole section and extended to the specimen surface along approximately perpendicular directions to the fracture branch initiated well connecting with the plane
A series of SC-CO2 fracturing and water fracturing experiments were conducted on planes and joint planes

Summary

Introduction

Shale gas is one of the unconventional resources which is stored in organic matter-rich shale formations. Due to the very small porosity (2% or less) and ultra-low permeability (0.1 to 0.0001 mD or even less) of shale, it is difficult to exploit shale gas by conventional oil and gas exploitation methods. In the past 20 years, the breakthrough of horizontal drilling and hydraulic fracturing technology has triggered the “Shale Oil and Gas Revolution” all over the world [3]. Hydraulic fracturing with multiple horizontal wells has been widely used in the exploitation of shale gas [4,5,6]. The hydraulic fracturing needs to consume a large amount of water and a typical shale gas well injects 2–4 million gallons of water into a deep shale reservoir, which is not conducive to the exploitation of shale gas reservoirs located in water shortage areas [7,8]. The injection of water will alter the distribution of Energies 2019, 12, 4229; doi:10.3390/en12224229 www.mdpi.com/journal/energies

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