Multiscale Characterization of Pore Structure and Mechanical Property of Organic-Rich Shale

The mechanisms of gas transport, rock deformation, and fracture initiation and propagation are critical to the improvement of hydraulic fracturing effectiveness and shale gas production. In this work, the multiscale pore structure in organic-rich shale is precisely characterized by using the combination of various 3D imaging techniques, including Micro-CT, focused-ion-beam/scanning-electron-microscopy (FIB/SEM), and focused-ion-beam/helium-ion-microscopy (FIB/HIM). The pores thought to be isolated with conventional imaging techniques are proved to be connected by higher-resolution imaging. Based on the pore structure characterization, we propose an image-based workflow for gas transport simulation. The simulations and experimental results are in good agreement. On the other hand, nanoindentation and microindentation are performed to characterize the elastic properties of the main constituents in shale at the mineral scale and the whole shale rock at the core scale, respectively. An upscaling scheme is proposed to predict the macroscopic properties based on the nanoindentation results. The predictions agree well with the microindentation measurements. In addition, micro-crack propagation in shale is investigated by using SEM in situ mechanical test technique. The videos of crack initiation and propagation process, as well as the corresponding load-displacement curves, are collected side-by-side. Various fracturing mechanisms are demonstrated through tests. In summary, by means of a variety of state-of-the-art experimental techniques, a systematic study of pore structure and mechanical property of organic-rich shale is provided. The application of these experimental techniques is also discussed in this work.