New method of in situ high-resolution experiments and analysis of fracture networks formed by hydraulic fracturing

Hydraulic fracturing plays a key role in the oil and gas development of unconventional tight reservoirs. Therefore, it is important to study the fracturing mechanism of rocks. Thus far, the exploration of this problem through laboratory experiments has been regarded as the best method. However, the current laboratory experiments cannot achieve in situ high-resolution observation and analysis. Accordingly, an online scanning platform composed of hydraulic fracturing and micro-computed tomography (HFCP) was developed in this study. The in situ measurements obtained using the HFCP include three parts: a computed tomography (CT) system with a maximum imaging resolution of 7 μm, a power system with a continuous changeable fluid pressure, and a post-processing system with rock reconstruction, grayscale calibration, threshold segmentation and efficient extraction of the fracture network. Furthermore, we carried out hydraulic fracturing experiments on tight sandstone samples using the HFCP, and the entire experimental process was conducted in situ. The statistics showed that under different confining pressures, the breakdown pressure and average fracture aperture increased with increasing injection rate, but the branch fracture volume fraction exhibited diverse characteristics. The HFCP provides a new method of studying the mechanism of the hydraulic fracturing of rocks, and it has the potential to reveal the in situ differences in fracture networks in tight reservoirs.