Numerical study of multi-stage hydraulic fracture propagation behaviors in triaxial stress state under different mining stages

Abstract

Hydraulic fracturing has been widely applied in underground mines for disaster prevention. The effectiveness is highly depended on the morphology of hydraulic fracture (HF), which, however, greatly affected by mining activities. Revealing the propagation behaviors of HF is of profound significance to understand the coupling of coal mining and hydraulic fracturing. In this paper, HF propagation was conducted based on lattice-spring method (LSM) after the analysis of mining-induced triaxial stress. The effects of mining stage, injection rate, and fracturing interval on HF propagation are investigated. The results show that mining-induced triaxial stress is beneficial to the formation of HF network. Once beyond rock failure pressure, increasing injection rate emphasized the stress shadow effect regardless of high or low stress state, resulting in crossing and diversion HFs. However, this effect was mitigated by broadening fracturing intervals which beneficial for vertical cessation HFs. Due to the complicated stress state in severely-affected stress region, the propagation length and angle of HF were influenced significantly, contributing to the occurrence of distortional HFs, HFs connection, and cross-layer phenomenon. Therefore, in the severely-affected stress region, an interlaced fracture network is likely to emerge, particularly in the case of narrow fracturing intervals and high injection rates. The research is committed to provide constructive suggestions for optimizing hydraulic fracturing under mining.