Strain localization in hydraulic fracturing of granite specimens based on DIC method

Abstract

Hydraulic fracturing is a crucial and widely-used technology in shale gas exploitation and enhanced geothermal systems, while the fundamental mechanisms of hydraulic fracturing are not comprehensively understood. This paper aims to promote the understanding of strain localization in hydraulic fracturing of granite specimens based on digital image correlation (DIC) method. Through a specially designed pressure enclosure, the hydraulic fracturing processes were captured by a high-speed camera. The strain localization phenomenon, evolution, and coalescence of SLZs in hydraulic fracturing were analyzed. Results show that obvious strain localization occurs before the specimen failure, which gradually develops into a continuous strain localization zone. With the evolution of SLZs, the specimen will be unable to bear the liquid pressure, and macro cracks occur at SLZs. The statistical data in the query region shows that the strain localization in hydraulic fracturing occurs earlier than previously thought, and the evolution of SLZs can be divided into steady, soaring, and fracture stages according to the changing trend. The coalescence of the patchy distribution SLZs occurs frequently throughout the evolution process of SLZs, and the coalescence of SLZs may be the cause of the increasing speed of evolution.

Method for macro-microscopic damage observation of rock hydraulic fracturing based on dic and thin section techniques

“…Based on DIC analysis, obvious strain localization phenomena was observed before the expansion of the hydraulically induced cracks [11,12], as shown in figure 5(a). Before failure, a clear strain localization zone appeared at the crack tip and gradually extended towards both ends of the sample over time, showing progressive damage evolution characteristics.…”

“…This facilitated the successful visualization of hydraulically induced crack propagation experiments, achieving high-precision displacement and strain fields using DIC analysis. Zhao et al [11] conducted experimental studies on fast granite and reported strain localization phenomena [12] and crack merging patterns [11] in hydraulically induced crack propagation, gaining a better understanding of the mechanism. Niu [9] adopted a "two rigid and one flexible" approach, realized true triaxial loading on a conventional biaxial testing machine, and conducted several experiments to study the crack propagation pattern and its influencing factors under true triaxial loading in hydraulic fracturing.…”