在模拟井下环境中堵剂的结构形成与失效机理

采用XRD，TG和SEM－EDS等研究了在模拟油井深处温度，压力条件下养护的G级油井水泥和YLD型堵漏剂浆体的水化产物和显微结构。在高温高压动态养护条件下，硬化水泥浆体内部存在大量CSH凝胶和Ca(OH2)晶体，而堵漏剂浆体的主要水化产物是CSH凝胶。在钢管－浆体界面，虽然水化程度更高，但CSH凝胶和Ca(OH)2晶体的量却很少；主要的水化产物是钙矾石和水化钙黄长石。界面处的显微结构也比浆体内部疏松。这表明在钢管－浆体界面处存在严重的溶蚀现象，导致水泥浆体很快损失胶凝性，这可能是水泥基堵剂失效的主要原因。堵漏剂浆体的溶蚀速率小于油井水泥浆体，其溶蚀表面可发生再水化过程，新生成的CSH凝胶具有修补受损界面的“自愈”作用，使堵漏剂浆体与钢管的粘结作用得以维持，从而延长堵漏剂的有效使用期。

MICROSTRUCTURE FORMATION AND INVALIDATION MECHANISM OF SEALANT IN THE SIMULATED ENVIRONMENT AT THE BOTTOM OF OIL-WELL

The hydration products and microstructure of Class G oil_well cement and YLD sealant pastes cured under the conditions of the simulated temperature and pressure at the bottom of oil_well were investigated with XRD, TG and SEM-EDS. There are abundant CSH gel and Ca(OH) 2 crystal formed inside the cement paste. The main hydration product of YLD sealant is CSH gel. However, there are seldom CSH gel and Ca(OH) 2 crystal formes at the interface between the cement paste and steel tube. The main hydrates are ettringite and gehlenite hydrate. The microstructure at the interface is not so dense as that in the paste, which causes serious leaching and a quick loss of cementing properties. Leaching also occurs at the interface between YLD sealant paste and the tube, but slower than in the case of the cement. A re_hydration process may take place at the interface and the newly formed CSH gel has self_healing effect to repair the damaged interface, which prolongs the life of the sealing by YLD sealant.