Review and prospect of coal rock hydraulic fracturing physical experimental research

Physical simulation of hydraulic fracturing is an approximate representation of fracture evolution and its dynamic process, which represents an important direction of fracture evolution research. Similarity theory is the theoretical basis of the transformation between field prototype and experimental model. Test equipment and similar materials are the material premise of physical simulation experiment. Monitoring and detection technology is the key part to evaluate the fracturing effect of hydraulic fracturing. This paper summarizes the development of similarity theory of hydraulic fracturing physical experiments, the evolution of experimental materials and devices, and the characteristics and application scope of common monitoring and detection methods from the above three aspects. The analysis shows that: the similarity criterion of hydraulic fracturing has been preliminarily formed, but it needs to be further modified according to the physical and mechanical properties of coal and rock. Numerical simulation method can be used to explore the influence degree of minor factors ignored in the derivation of similarity criterion, so as to improve the reliability and applicability of the empirical equation. In view of various physical and mechanical properties of coal and rock, many empirical formula equations of similar materials have been obtained at present, but a set of detailed experimental specification and a large number of experimental attempts are still needed to improve the repeatability of the experiments, so as to establish a more universal database of empirical equations of similar material matching. Fracturing devices are developing towards the direction of multi-field coupling with more simulation conditions, larger simulation scale and wider simulation range, and fracturing methods are gradually diversified with engineering applications. However, the accuracy of triaxial loading of fracturing devices needs to be further improved to ensure effective fracturing experiments under high stress conditions, and reduce the impact of experimental operations on the final results. Monitoring methods and detection technologies have their own advantages in evaluating the fracturing effect of hydraulic fracturing, and similar materials also have a significant impact on the effectiveness and accuracy of monitoring methods and detection technologies. How to rationally select and combine monitoring methods and detection technologies based on experiments is the key to meet the research needs of micro-structures.