Investigation on the propagation characteristics of tensile fractures crossing interfaces within dry hot rock reservoirs based on the Brazilian split test

Abstract

An in-depth exploration of the expansion behavior of hydraulic fractures across natural interfaces holds significant engineering importance for enhancing geothermal exploitation of dry hot rock reservoirs. In this research, two types of granite specimens featuring distinct cementation strength characteristics were chosen to investigate the behavior of hydraulic fractures extending across the interface under diverse loading angles. Firstly, X-ray diffraction (XRD) and polarizing microscopy were employed to analyze the mineral composition and distribution disparities at the granite interface and on either side. Subsequently, the Brazilian split test was performed on the two granite specimens with natural interfaces using the acoustic emission (AE) system and digital image correlation (DIC) method at five loading angles. The results demonstrate that the extension behavior of hydraulic fractures in granite is profoundly influenced by the loading angle, the cementation strength of the interface, and the physical property discrepancies between the two sides of the interface. The tensile strength of both granites ascends initially and then descends as the loading angle increases. The mineral composition content and spatial distribution characteristics of the granite interface on both sides determine the physical property differences between the two sides of the interface. The main fracture formed in granite is more prone to shift towards the side of the weaker material, and secondary fractures are more likely to occur in the area of the weaker material. These discoveries are anticipated to furnish theoretical guidance for the development of hydraulic fracturing technology for dry hot rock reservoirs.