A laboratory study of microcracks variations in shale induced by temperature change

•Effects of hydration and temperature were studied separately by over 40 CT tests.•Temperature change is driving force of fracture propagation for hydrated shales.•Area growth ratio of rapid cooling was more than 3 times that of gradual heating.•Hydration coupled with temperature was 1.5 times more effective than single effect.•Two suggestions for fracturing and soaking.