In situ dynamic X-ray imaging of fluid-rock interactions inside tight sandstone during hydraulic fracturing: fluid flow process and fracture network growth

Hydraulic fracturing plays a fundamental role in unconventional hydrocarbon production and the development of enhanced geothermal systems. Thus, studying the fluid flow process and fracture network growth during hydraulic fracturing is necessary to provide guidance for creating and sustaining fracture networks in target reservoirs. The actual formation stress state and hydraulic fracturing process can be simulated in the laboratory for small-scale rock samples in hydraulic fracturing experiments. High-energy industrial X-ray computed tomography (CT) has been used to directly track the fracture propagation in millimeter-scale samples under triaxial stress loading. In this study, a large-scale fracture network with economic benefits for unconventional energy exploitation was the target of the experiment; therefore, centimeter-scale samples were used. A hydraulic fracturing simulation experiment was conducted on tight sandstone by applying triaxial compression and injection pressures. With the assistance of the PEEK core holder and third-generation medical X-ray CT scanner, in situ dynamic X-ray imaging of the fluid-rock interactions inside the sample was conducted for the first time. The fluid-rock interactions and fracture network growth can be dynamically observed, revealing the fluid-rock interactions during the hydraulic fracturing process and how macroscopic failure develops from the microfracture.