A Digital Rock Physics-Based Multiscale Multicomponent Model Construction of Hot-Dry Rocks and Microscopic Analysis of Acoustic Properties under High-Temperature Conditions

Abstract

Summary The development of hot-dry rock (HDR) resources relies on the accurate evaluation of acoustic properties. The acoustic properties are usually measured by rock physical experiments. However, the high-temperature heating experiment is difficult because of high costs, long time-consumption, and complex operations. Hence, digital rock physics (DRP), a less time-consuming and more economical way, is used to analyze the acoustic properties. Here, multiple scanning experiments, including X-ray computed tomography (X-ray CT) for reconstructing 3D model, quantitative evaluation of materials by scanning electron microscopy (QEMSCAN), and modular automated processing system (MAPS), are conducted, and a fusion method of multiple scanning images is proposed to solve the contradiction between image resolution and the sample size caused by small pore size and complex mineral distribution and to generate the multiscale multicomponent digital rock. Then, the acoustic numerical modeling at high temperatures is conducted, where the essential idea is to derive the theoretical correlation between the elastic moduli of the minerals and the temperatures to obtain the elastic moduli of minerals at different temperatures. Finally, the acoustic properties of the digital rock are calculated, and the microscopic mechanism at high temperatures is studied in detail. The simulating results demonstrate that bulk modulus, shear modulus, Poisson’s ratio, Young’s modulus, P-wave velocity, and S-wave velocity decrease as the temperature rises. More importantly, the thermal cracking behavior of HDR is represented, and fractal Brown motion is utilized to generate the fractured digital rock. The simulation results of fractured digital rock illustrate that it is the fracture to cause rapid decline of acoustic properties after 250℃. Overall, this pore-scale work accurately illustrates the acoustic properties of HDR and provides a new idea to study the rock physics properties at high temperatures and a microscopic interpretation for geothermal fracturing development.