Experimental Research and Fractal Analysis of Supercritical CO<sub>2</sub> Pneumatic Fracturing under True Triaxial Stress
Xiaofei Wang, Shaobin Hu, Enyuan Wang
Abstract
Supercritical CO 2 pneumatic fracturing technology has promising applications in petroleum and shale gas extraction. A true triaxial supercritical CO 2 pneumatic fracturing experimental system was developed, and nine sets of experiments were conducted to study the fracturing effect of different polyenergy agent dosage and various CO 2 pressure. The pressure profile of the fracture tube demonstrated that an increase in the initial CO 2 pressure at the same dosage resulted in a better fracturing effect, with little change in the fracturing effect at the same initial pressure at sufficient dosage. The tensile stresses generated by the shock wave reflection were responsible for the micro-annular cracks. The binarized fractal distribution had a clear fractal character, and there was a well linear fit between the fractal dimension F d and the damage variable w (defined by the crack area). The computation of the fractal dimension contained information on the crack morphology, thus using the fractal dimension as the damage variable provided a more comprehensive description of the damage. The study provided the basis for engineering problems in the field of new waterless fracturing technology for supercritical CO 2 in shale gas extraction, where future monitoring of temperature changes in the fractured tube is required.