Study on the influence of stress differences on hydraulic fracturing based on true triaxial experiments and discrete element numerical simulations

Abstract

Laboratory experiments are an effective way to study the initiation and propagation of hydraulic fractures for the complex stress level and structure of underground reservoirs. However, it is difficult to observe hydraulic fractures directly in rock or mortar specimens. In this study, a kind of transparent rock-like material whose tension–compression ratio reaches 1/9.5 at normal temperature was obtained, which helped us to observe fractures directly. Using transparent specimens, triaxial hydraulic-fracturing experiments were carried out to explore the influence of stress differences on the initiation pressure and propagation of hydraulic fractures. The initiation pressure decreased with increasing stress difference, and the hydraulic cracks propagated along the maximum stress direction. The DEM (Discrete Element Method) simulation of hydraulic fracturing was used to verify the results derived from the laboratory experiments. This study provides new insights into the propagation of hydraulic fractures.