Data from: Study of mixed mode fracture toughness and fracture trajectories in gypsum interlayers in corrosive environment

Based on the engineering background of water dissolving mining for hydrocarbon storage in multi-laminated salt stratum, the mixed mode fracture toughness and fracture trajectory of gypsum interlayers soaked in half-saturated brine at various temperatures (20°C, 50°C and 80°C) were studied by using CSNBD (centrally straight-notched Brazilian disc) specimens with required inclination angles (0°, 7°, 15°, 22°, 30°, 45°, 60°, 75°, 90°) and SEM (scanning electron microscopy). The results showed: (i) The fracture load of gypsum specimens first decreased then increased with increasing inclination angle, due to the effect of friction coefficient. When soaked in brine, the fracture toughness of gypsum specimens gradually decreased with increasing brine temperature. (ii) When soaked in brine, the crystal boundaries of gypsum separated and became clearer, and the boundaries became more open between the crystals with increasing brine temperature. Besides, tensile micro-cracks appeared on the gypsum crystals when soaked in 50°C brine, and the intensity of tensile cracks became more severe when soaking in 80°C brine. (iii) The experimental fracture envelopes derived from the conventional fracture criteria and lay outside these conventional criteria. The experimental fracture envelopes were dependent on the brine temperature and gradually expanded outward as brine temperature increases. (iv) The size of FPZ (fracture process zone) was greatly dependent on the damage degree of materials and gradually increased with increase of brine temperature. The study has important implication for the control of shape and size of salt cavern.

本研究以多层盐层油气储库水溶开采工程为背景，采用不同倾角（0°、7°、15°、22°、30°、45°、60°、75°、90°）的中心直切槽巴西圆盘（centrally straight-notched Brazilian disc，CSNBD）试样，结合扫描电子显微镜（scanning electron microscopy，SEM），对半饱和卤水浸泡下不同温度（20℃、50℃、80℃）时石膏夹层的复合型断裂韧性与断裂轨迹开展了实验研究。结果表明：(i) 受摩擦系数影响，石膏试样的断裂载荷随倾角增大先降低后升高；经卤水浸泡后，石膏试样的断裂韧性随卤水温度升高逐渐降低。(ii) 经卤水浸泡后，石膏的晶界发生分离且愈发清晰，随着卤水温度升高，晶体间的边界张开程度愈发明显；此外，在50℃卤水中浸泡时，石膏晶体上出现拉伸微裂纹，而在80℃卤水中浸泡时，拉伸裂纹的严重程度进一步加剧。(iii) 基于常规断裂准则推导得到的实验断裂包络线位于该类常规准则的适用范围之外，且实验断裂包络线依赖于卤水温度，随卤水温度升高逐渐向外扩展。(iv) 断裂过程区（fracture process zone，FPZ）的尺寸极大程度依赖于材料的损伤程度，并随卤水温度升高逐渐增大。本研究对盐穴形状与尺寸的调控具有重要的指导意义。