The effect of shale bedding on supercritical CO2 jet fracturing: A experimental study

Abstract

The bedding plane of shale is related to anisotropic mechanical property, which apparently affects the shale fracturing. To investigate the influence of shale bedding on the fracture morphology and perforation damage under Supercritical Carbon Dioxide (SC–CO2) jet fracturing, the experiments were comprehensively studied via the macro fracture analysis, strain monitoring, Scanning Electron Microscope (SEM) test and Energy Dispersive Spectroscopy (EDS) test. The results demonstrated that the average Young's Modulus (YM) and Uniaxial Compressive Strength (UCS) of shale specimen with the bedding plane angle of 0° is 9.37 times and 2.89 times of the shale specimen with bedding plane angle of 90°, respectively. During jet fracturing, both the jet pressure and existing bedding are beneficial for fracture initiating and propagating naturally along the weak bedding planes, and shear fracture can enhance the fracture complexity. When the perforation distributes in the direction perpendicular to the bedding plane, the less strain can be obtained, and the mass loss and CO2 absorption of shale specimen significantly increase by 350% and 300%, respectively, as the jet pressure increases from 25 MPa to 50 MPa, which is larger than the shale specimen with bedding plane angle of 0°. The perforation damage is explored after jet fracturing via SEM and EDS, and it is found the direction of perforation perpendicular to the bedding plane is beneficial for micro-cracks generation, and leads to 10% decline of carbon (C) and oxygen (O) elements in the samples. These studies clearly show the influence of the bedding plane angle on the fracture morphology and perforation damage, which are crucial for SC-CO2 fracturing and CO2 storage in shale reservoir.