Effects of Pressurizing Cryogenic Treatments on Physical and Mechanical Properties of Shale Core Samples—An Experimental Study

Abstract

The technique of cryogenic treatments requires injecting extremely cold fluids such as liquid nitrogen (LN2) into formations to create fractures in addition to connecting pre-existing fracture networks. This study investigated the effects of implementing and pressurizing cryogenic treatment on the physical (porosity and permeability) and mechanical properties (Young’s modulus, Poisson’s ratio, and bulk compressibility) of the Marcellus shale samples. Ten Marcellus core samples were inserted in a core holder and heated to 66 °C using an oven. Then, LN2 (−177 °C) was injected into the samples at approximately 0.14 MPa. Nitrogen was used to pressurize nine samples at injection pressures of 1.38, 2.76, and 4.14 MPa while the tenth core sample was not pressurized. Using a cryogenic pressure transducer and a T-type thermocouple, the pressure and temperature of the core holder were monitored and recorded during the test. The core samples were scanned using a computed tomography (CT) scanner, and their porosities, permeability, and ultrasonic velocities were measured both before and after conducting the cryogenic treatments. The analyses of CT scan results illustrated that conducting cryogenic treatments created new cracks inside all the samples. These cracks increased the pore volume, and as a result, the porosity, permeability, and bulk compressibility of the core samples increased. The creations of the new cracks also resulted in reductions in the compressional and shear velocities of the samples, and as a result, decreasing the Young’s modulus and Poisson’s ratio. Moreover, the results revealed that pressurizing the injected LN2 increased the alterations of aforementioned properties.