Investigating Effects of Thermal Shock Technique on Unconventional Reservoir Rock Mechanical Properties

In thermal shocking, a cold fluid is injected into a hot formation to generate thermal shocks. These shocks can create fractures in the surface of the formation, which can connect with natural networks of fractures. This study assessed the capacity of thermal shocking with cold nitrogen gas to initiate fractures in shale-oil and shale-gas reservoirs. Two core samples were used in a series of experiments. These samples were heated at 82 °C (180 °F) for one hour and then rapidly cooled in three thermal shocks. In each shock, nitrogen at -18 °C (0 °F) was injected at approximately 1,000 psi for about 5 minutes. Ultrasonic velocity tests were performed before and after each shock. Computed tomography (CT) scanner was used to scan the core samples before and after performing the experiment. The results of these experiments were very promising: the thermal shocking generated cracks on the surfaces of the samples, and altered their Young’s moduli, Poisson’s ratios, and brittleness ratios. These results support the conclusions that thermal shocking can be used to create fracture in shale formations and that thermal shocking can thus be considered an alternative to conventional hydraulic fracturing, which relies on water-based fluids.