页岩气水平井固井二界面油基泥饼化学活化方法与固化交联机理研究

Sustained annular pressure (sustained casing pressure) is a problem involving the complex theory and technology for obtaining maximum productivity of horizontal shale gas wells. One of its important reasons is the isolation failure of cement-formation interface. The key to solve this problem is to achieve oil-based mud cake solidification and interfacial crosslinking among cement, oil-based mud cake and formation. Well then, can it be achieved when the oil-based drilling fluid and cement slurry are kept unchanged? Based on the self-established experimental system which simulates cement-formation interface, the conditions, method and mechanism of the chemical activation of organobentonite in the oil-based mud cake in horizontal shale gas well is explored emphatically combined with the modern testing technology and quantitative simulation experimental method. Then the mechanism of oil-based mud cake solidification and interfacial crosslinking at cement-formation interface is studied deeply, and their reliable evidences can be obtained. They will provide scientific basis and technical support for solving the problem of sustained annular pressure in horizontal shale gas wells. Through this study, it intends to reveal the evolution law of electron binding energy and element state on the surface of organobentonite particles in the oil-based mud cake. Then it plans to explore the characters of resultants in the solidified oil-based mud cake and crosslinking network structure, and their chemical reaction mechanisms can be proposed. In view of this, the new materials used for oil-based mud cake solidification can be developed, and their compatibility and responsiveness will be studied. Then a new method which can significantly improve the shearing strength at cement-formation interface in horizontal shale gas wells is established. At last, the actual effect of this theory and method is verified by their applications in the national shale gas project demonstration area.

环空带压是页岩气水平井获得最大产能亟待解决的一个复杂性理论和技术难题，而固井二界面封隔失效是引起环空带压的一个重要原因，解决之关键是油基泥饼固化和界面交联。那么，在油基钻井液和水泥浆均不变的条件下能实现吗？本项目基于自主建立的固井二界面仿真实验系统，拟用现代分析测试技术和定量模拟实验方法，着重探索井内油基泥饼有机土化学活化的条件、方法和机理，深入研究固井二界面油基泥饼固化机理与界面交联机制，获得油基泥饼固化与界面交联的可靠证据，为解决页岩气水平井环空带压难题提供科学依据和技术支持。通过本项研究，揭示油基泥饼有机土颗粒表面电子结合能和元素状态的演化规律，探明固化油基泥饼和交联网络结构的生成物性状，提出油基泥饼固化和界面交联的化学反应机理；创制出油基泥饼固化材料，明确油基泥饼固化材料的适应性和响应性，创建一套能大幅提高页岩气水平井固井二界面胶结强度的新方法；选定页岩气示范区，验证理论方法实效。

自2017年8月获批以来，通过4年多的研究，已全面完成了项目的各项研究内容。通过本项目的研究，创立了油基钻井液和水泥浆不变条件下固井二界面油基泥饼固化（Oil-based Mudcake Solidification，即OMS）胶结理论（一是油基泥饼内有机土转化为类无机土的化学反应机理，二是油基泥饼固化机理，三是水泥环-固化油基泥饼-地层三者之间的交联机制），获得了OMS的实验证据（即一是油基泥饼内有机土转化为类无机土前后的组成和结构；二是油基泥饼固化和界面交联的生成物性状和微观结构；三是研究后的固井二界面胶结强度较研究前的最高提高了101.2倍）；创新设计并制备出油基泥饼固化材料（共三种：其中一种材料已申请国家发明专利，即名称为一种油基泥饼固化剂及其制备方法、使用方法与用途，申请号：202110655223.1），形成了OMS固井新技术，为解决页岩气水平井环空带压难题提供了一种新理论和一条新途径。为了验证本项目理论研究成果的实用性和有效性，创制出油基泥饼固化剂（70立方米），截止2021年12月底已在四川、重庆、贵州等页岩气水平井中完成了8口井的现场试验验证与应用，效果显著：固井施工一次成功率100%，固井质量合格率100%（一界面优良率90%以上，二界面胶结中等以上的86.7%），且8口井压裂前后均未出现环空带压，即压裂前后环空带压率均大幅度降低。目前，该新技术已在四川、重庆、贵州等页岩气水平井完井固井中推广应用。已发表学术论文16篇（12篇已被SCI收录/EI收录），申请国家发明专利1项，培养毕业硕士研究生7名（硕士研究生5名，博士研究生2名）；培养学术骨干1名（即1名项目组成员于2020年12月从讲师升任副教授）。通过本项目4年多的理论探索与研究、新材料研制与改进、现场试验与应用，达成了基础研究（发表16篇论文）、技术研发（申请发明专利1项）、工程应用（现场应用8口井且效果显著）的相互协同，即较好地实现了基础研究成果走向应用。