Hydraulic Fracturing of a Tight Conglomerate Sample with Distributed Optical Fibre Monitoring

ABSTRACT In this paper, a distributed fiber-optic monitoring system is used to finely portray the effect of gravel on crack extension during a true triaxial physical simulation experiment. The experimental results show that under the control of stress difference, the obstruction effect of large-grained gravels on cracks is much higher than that of small-grained gravels on cracks. The fracture encounters the large-grained gravels to wind around the gravels mainly, and the fracture produces more microfractures within the rock. The waterfall cloud map shows a greater variation in the stretching and compression regions. When the fractures encounter small gravels, the fractures are still predominantly gravel-wrapping with some gravel penetration, and the strain distribution on the waterfall cloud diagram is uniform. When the gravel is disordered, the fracture morphology is complex and diverse. INTRODUCTION Conglomerate reservoirs are low porosity and low permeability. Hydraulic fracturing technology contributes to the efficient development of conglomerate reservoirs. The shape of the sewing mesh after pressing affects the final production result (Kang et al., 2020). Conglomerate reservoirs, another key development target in China after shale, have large development potential. Due to the high non-homogeneity of conglomerate, The extension of fractures in conglomerate reservoirs is affected by complex mechanisms, and characterization of fracture morphology is more difficult (Tang et al., 2022). Some scholars have conducted indoor experimental studies on the hydraulic fracture morphology of conglomerate reservoirs. Ren et al. found that hydraulic fractures extend along the edges of conglomerate grains by large-scale physical simulations with conglomerate outcrops (Ren et al., 2023). Liu et al. used the baikouquan formation of the Mahu depression as the object of study. The indentation hardness tests found that the gravel was 5.3 times harder than matrix hardness (Liu et al., 2014). Li experimentally clarified several forms of fractures and gravels (Li et al., 2013).