Design and Application of an Integrated Experimental Apparatus for Shale Scratch and Indentation Based on an In-Situ Environment

Abstract The proven reserves of shale oil are continuously increasing, with hydraulic fracturing being the key technology enabling its commercial exploitation. Compressive strength, fracture toughness, and hardness are important parameters reflecting the mechanical properties of shale. Research on these parameters can effectively guide fracturing operations and help identify optimal fracturing zones. Given this, it is of great significance to understand the mechanical properties of the entire shale formation. This study designs an experimental apparatus for the integrated measurement of shale scratch and indentation based on an in-situ environment. The system combines the functions of shale scratch and indentation tests, allowing for scratch and indentation experiments by simply replacing the blade and adjusting program instructions. This novel scratch system enables continuous measurement of shale mechanical properties at an engineering scale. The designed temperature-pressure device replicates reservoir conditions. The device was used to evaluate the mechanical characteristics of various lithofacies in the shale basin. Results are as follows. The device primarily consists of a scratch and indentation execution system, a data acquisition system, and a data processing system. The scratch and indentation execution system includes a horizontal movement subsystem, a vertical movement subsystem, and an execution blade, among others. These subsystems collaborate to conduct scratch and indentation experiments. The temperature-pressure device can simulate reservoir conditions for scratch and indentation experiments at temperatures ranging from room temperature to 150 ℃, and pressures ranging from 0.1 to 27 MPa. The device has been used to evaluate the mechanical characteristics and compressibility of four common shale lithofacies in the Songliao Basin. The study analyzed the evolution of shale mechanical properties under the influence of lamination, microfractures, and mineral composition. Different types of shale exhibit varying levels of fracturability, with siltstone shale demonstrating the highest fracturability, followed by laminated feisic shale, laminated diamictic shale, and finally, foliaceous shale. Compared to conventional mechanical experiments and well logging results, the design of this experimental apparatus provides a convenient, economical, and precise method to study the mechanical properties of shale. The measurement results exhibit continuous variations and achieve millimeter-level accuracy, providing a robust theoretical foundation for hydraulic fracturing operations and identification of the optimal fracturing zones.