Analysis of fracture network development in Oimasha granite samples by thermal gradients and dehydration in experiments at 600°C

Abstract

The mechanisms underlying the growth of fracture networks in Oimasha granite sub- jected to heating at 600◦C were investigated. A combination of thermogravimetric anal- ysis (TGA) and Python-based image processing was employed to track the evolution of these fractures post-heating. Results revealed a substantial 26% increase in the total fracture area and a 19% surge in the number of fracture branches. Notably, the average branch length remained remarkably stable, suggesting that new cracks exhibit a similar scale to those already present. Because the orientation of the new fractures was observed to be random, thermal gradients were determined not to be the primary driving force. Instead, significantly higher fracture densities were identified around water-bearing min- erals such as chlorite and sericite, pointing to dehydration and fluid decrepitation as the primary catalysts. These findings were corroborated by TGA data, which demonstrated a weight loss of 0.334wt-% as trapped water was released during the heating process. While Python scripts were utilized for the rapid quantification of crack networks, man- ual oversight was still required to accurately distinguish between fracture types. These results contribute to a more comprehensive understanding of rock stability in high-heat environments, particularly for applications in geothermal energy. Finally, the use of real- time acoustic sensors is proposed for future research to pinpoint the precise temperature at which fluid-driven cracks initiate.