Insight into the fracturing of silty mudstone in cyclic hydrothermal environments based on computed tomography

Abstract

The objective of this study was to examine the fracture evolution and related mechanism of silty mudstone in cyclic hydrothermal environments. Fracture evolution tests and computed tomography (CT) scans were carried out on silty mudstone specimens subjected to cyclic wetting-heating. The spatial–temporal variations of fracture parameters including the total length ratio, fracture rate, mean fracture width, fracture direction and fractal dimension were investigated. The mechanism underlying the fracture evolution in silty mudstone was also analyzed. The results show that fractures initiate and propagate from the wetting-heating surface down to the deep layer with increasing cycle number. Most of the fractures are parallel or perpendicular to each other and form a reticulate fracture network on every horizontal cross-section. The total length ratio, fracture rate, mean fracture width and fractal dimension considerably decrease as the depth increases, and the total length ratio and fracture rate significantly increase with increasing cycle number. After a wetting-heating cycle, only the zone within a depth of 14 mm shows slight fracturing; however, after 17 wetting-heating cycles, slight fracturing occurs within a depth of 104 mm. The fracture mechanism mainly involves the hydrothermal stress effect, water-softening effect, and mineral hydrolysis.