固井二界面弹性化泥饼形成机理与密封特性

The mud cake being unable to solidify formed after the well cementation is the primary cause for the fluid channeling. At present, the mud cake removal technology and the mud cake solidification technology are difficult to fundamentally solve the problem of the fluid channeling through the mud cake. Therefore, the concept of elastification of mud cake was put forward in this application. The construction technology of the mud cake solidification technology and the underground crosslinked gel water shutoff agent which is used maturely in the profile control and water shutoff field were used for reference. The elastification agent was introduced in the preflush, and the elastification agent was injected into the mud cake through the fluid loss of the preflush. The bentonite and the drilling fluid additive existed in the mud cake could react with the elastification agent to form a crosslinked gel, which is the elastification of the mud cake. To realize the elastification of the mud cake, the material composition change of the mud cake with the injection of the elastification agent, the effect of the material composition of the mud cake on the structure and property of the mud cake, and the effect of elasticity modulus and other factors on the sealing character of the mud cake will be studied in this project. By the study mentioned above, the relation between material composition of the mud cake and the injection degree of the elastification agent, the relation between the structure and property of the elastification mud cake, and forecasting model about the sealing ability of the elastification mud cake could be obtained. The performance optimization of the elastification mud cake could be realized by the forecasting model and the relation between the structure and property of the elastification mud cake. The study and the result mentioned above could provide theory and technology support for the realization of the elastification of the mud cake and enhancing the sealing ability of the mud cake.

固井二界面残留的钻井液泥饼是引起环空窜流的主要原因之一。鉴于难以实现泥饼的彻底清除，泥饼固化技术形成的泥饼固化物在压裂等措施下发生破坏的风险较大，难以根本解决流体经泥饼窜流的难题。借鉴调剖堵水领域成胶时间可控的地下交联凝胶堵水剂及泥饼固化技术的施工工艺，本项目提出了实现泥饼弹性化的技术思路，在固井前置液或水泥浆中加入弹性化剂，通过前置液或水泥浆的失水使弹性化剂渗入泥饼，与泥饼中的膨润土及钻井液外加剂发生交联，实现泥饼弹性化。通过研究泥饼物质组成随弹性化剂注入的变化规律，明确弹性化剂在泥饼中的侵入程度与泥饼物质组成的关系；研究泥饼物质组成对弹性化泥饼结构与性能的影响，明确弹性化泥饼结构与性能的关系；研究弹性模量等因素对弹性化泥饼密封特性的影响，建立密封能力预测模型，基于建立的模型及泥饼结构与性能的关系对弹性化泥饼性能进行优化。为实现泥饼的弹性化及增强泥饼的密封能力，提供理论基础与技术支撑。

油气井固井结束后，在固井二界面处会有一层泥饼残留，这层泥饼的存在容易导致环空二界面密封失效，同时也是导致环空水泥环整体密封能力失效的关键。本项目在泥饼固化技术的实验方法和实验思路的基础上，基于吸水树脂的成胶原理，提出了泥饼弹性化方法。该方法以固井流体作为依托介质，不改变钻井液组成与性能，将弹性化剂置于固井流体（主要是前置液）中，弹性化剂在固井流体向地层中的滤失过程中被带入泥饼中，通过控制泥饼成胶时间使其在注水泥结束后发生交联反应实现泥饼转化成弹性化泥饼。.为了优选出对弹性化泥饼具有良好作用性能的弹性化剂及钻井液外加剂，本项目通过混掺的方式制备黏土和弹性化剂的聚合物试样，通过测试试样的抗压恢复率、吸水倍率得出了成胶性能最优的弹性化剂配方，明确了钻井液外加剂对试样性能的影响规律。通过室内实验，研究了挤入压力、挤入时间、弹性化剂浓度对弹性化泥饼性能的影响规律，并对弹性化泥饼的微观结构进行了分析表征。最后实验研究了弹性化泥饼对环空密封性能的影响。.研究结果表明，以丙烯酰胺、N、N-亚甲基双丙烯酰、过硫酸铵为弹性化剂可以制备出抗压恢复率、抗拉强度等性能较好的弹性化泥饼。随着挤入压力、挤入时间、弹性化剂浓度的逐渐增加，弹性化泥饼的性能逐渐改善并趋于稳定。钻井液外加剂对弹性化泥饼的性能有较大影响，但是不影响弹性化泥饼的成胶性。与未弹性化的泥饼相比，弹性化泥饼有较好的抗冲击破坏能力和耐水冲刷破坏能力，可较好的改善环空二界面的持久密封性能。本项目的研究，对拓展凝胶的理论和制备方法具有一定科学意义。通过本项目的研究，揭示了弹性化泥饼的形成机理，明确了现场施工参数、钻井液外加剂对泥饼弹性化技术的影响，对指导泥饼弹性化技术的施工具有重要的现实意义。