Mechanism of microfracture propagation under mechanical–chemical coupling conditions considering dissolution

Abstract

Microfracture propagation is well known to significantly impact the stability of well bores in shale formations; however, there is a lack of research on the role of dissolution. Herein, a shale microfracture propagation model is constructed that couples mechanics and chemistry by considering hydration, capillary, strength weakening, and dissolution effects. Combining relevant experiments with the model reveals the mechanism of microfracture propagation. Results indicate that ΔK(stress intensity factor) shows an upward trend with increasing hydration micromechanical forces and when hydration time exceeds 30 h, the rate of increase in ΔK gradually slows down. ΔK increases linearly with tensile strength. When the yield zone length “a” remains constant, ΔK first decreases and then increases with increasing a/b ratio, reaching its minimum value when the a/b ratio is 0.6. ΔK shows a linear increase with interfacial tension and decreases with increasing wetting angle and initiation angle of cracking. The dissolution of carbonate minerals can considerably influence the propagation of microcracks. Initially, the impact of this dissolution may not be pronounced; however, as the duration of the rock samples' exposure to the dissolution process exceeds 100 h, the increase in the stress intensity factor becomes substantial. The increase in ΔK accelerates the propagation of microcracks within rocks. Constructing a shale microfracture propagation model based on dissolution effects is crucial for elucidating the microscopic mechanisms of mechanical–chemical coupled changes in shale microfractures, which is significant for analyzing wellbore stability.