Abstract: Aiming at the problem that the micro-fractures of the cement sheath destroy the integrity of the cement sheath, this work successfully prepared an oil-water dual-response self-healing material using sodium silicate as a self-healing agent, diatomite as a carrier, and ethyl cellulose as a surface coating material, and evaluated its self-healing effect. The results showed that the optimum calcination temperature of diatomite was 600℃. At this time, the specific surface area and pore volume of diatomite were the largest, and the pore distribution was uniform, which was most conducive to the adsorption of sodium silicate. Ethyl cellulose did not react with sodium silicate and diatomite. The 2wt% ethyl cellulose solution had the best coating effect on sodium silicate, and could form a smooth and dense film on the surface of diatomite adsorbed with sodium silicate. The optimum content of coated self-healing material in cement was 4wt%. After 14 days of self-healing, the micro-cracks of cement paste were completely closed, and the permeability of cement paste decreased to 0.31 mD, which was 69.31% lower than that of blank cement paste. After 14 days of self-healing, the compressive strength of cement paste with 4wt% coated self-healing material reached 26.6±1.3 MPa, and the recovery rate of compressive strength was 85.3%, which was 2.1 times that of blank cement paste. It was found by data fitting that the compressive strength recovery rate of cement paste increased first and then decreased with the increase of self-healing material content, and the self-healing effect was the best when the content was 4.5wt%. The results of XRD and TG analysis showed that when cracks occurred in the cement paste, the ethyl cellulose film on the surface of the self-healing material dissolved in oil, and then the self-healing agent sodium silicate consumed calcium hydroxide and water in the cement paste to form hydrated calcium silicate, and then filled the cracks to achieve self-healing.

Key words: cementing cement sheath, micro-crack, oil-water dual-response, self-healing materials, permeability, compressive strength recovery rate

摘要： 针对固井水泥环微裂缝破坏其完整性的问题，本工作以硅酸钠为自修复剂、硅藻土为载体、乙基纤维素为表面包覆材料，成功制备了油水双响应型包覆式自修复材料，并系统评价其对水泥石的自修复效果。结果表明，硅藻土的最佳煅烧温度为600℃，此温度下制备的硅藻土具有最大的比表面积和孔体积，且孔洞分布均匀，对硅酸钠的吸附性能最优。乙基纤维素与硅酸钠、硅藻土均无化学反应，其中2wt%乙基纤维素溶液的包覆效果最佳，可在吸附硅酸钠的硅藻土表面形成一层平整光滑且致密的包覆膜。包覆型自修复材料在水泥中的最佳掺量为4wt%。自修复14 d后，水泥石微裂缝完全闭合，渗透率降至0.31 mD，较空白水泥石降低69.31%；同时，其抗压强度达到26.6±1.3 MPa，抗压强度恢复率高达85.3%，为空白水泥石同期恢复率的2.1倍。经数据拟合发现，水泥石抗压强度恢复率随自修复材料掺量的增加呈先上升后下降趋势，4.5wt%掺量时自修复效果最佳。结合X射线衍射和热重分析结果可知，当水泥石中产生微裂缝时，自修复材料表面的乙基纤维素膜遇油溶解，随后自修复剂硅酸钠消耗水泥石中的氢氧化钙和水反应生成水化硅酸钙，进而填充裂缝实现自修复。

关键词: 固井水泥环, 微裂缝, 油水双响应, 自修复材料, 渗透率, 抗压强度恢复率