盐穴储气库薄互层岩体顶板封闭性机制研究

This project aims at the key scientific issue in the sealability mechanism and assessment of the low grade thin interbedded salt rock cavern roof, to conduct experimental and theoretical study by depending on the demonstration projects of Huai’an underground salt gas storages. The main investigative contents includes: as for the high impure salt rock in roof strata, the stress-percolation coupling tests are to be conducted under variable stress regime, then the permeability evolution law and the onset condition of leakage are to be indicated and the corresponding percolation model and dilatancy-criterion are to be established. As for the different types of interfaces which connect the mudstone interlayer and salt rock layer, mechanical testing as well as permeability coupling testing is to be carried out. Micro-survey and observation of thin slices will be supplemented to investigate the fracture features of the interface. And then the control criteria of fracture and the decision condition of local percolation channels formation around the interface are to be proposed, respectively. In the end, the percolation model, control criteria as well as decision condition are to be verified and improved by comparing with the field measurements, and then the theory and method on evaluating the sealability of the low grade thin interbedded salt rock roof are to be formed. The results of this project can provide significant references for geological strata selection, roof designing and tightness assessment of the salt cavern in domestic.

本项目紧密围绕我国盐穴储气库低品位薄互层盐岩顶板封闭性机制这一关键科学问题，依托江苏淮安盐穴储气库工程，开展试验和理论研究。主要研究内容为：针对典型薄互层盐岩顶板中高杂质盐岩层，开展储库运行时各种应力状态下的气固耦合的室内模拟试验研究，探明盐岩的渗透演化规律及发生渗漏的条件，建立相应的渗透模型及扩容准则；针对薄互层盐岩顶板中的盐岩-泥岩交界面，开展力学及渗透耦合试验，辅以细观观察及切片技术，揭示交界面局部破损的演化特征，建立交界面破坏控制判据及渗漏局部通道形成的判定条件；最后，结合数值模拟及现场测试对相关模型及判据进行检验和修正，形成储气库低品位薄互层盐岩顶板封闭性能评价的理论和方法。研究成果可为我国盐穴储气库的地层选段、顶板设计及封闭性评价等提供重要依据。

天然气是重要的清洁能源，对于碳减排及雾霾治理具有重要的意义。我国的天然气消费逐年升高，对外依存度也高达45%。但我国天然气生产区主要位于西部，而消费区主要在中东部。为了保障天然气消费的安全，必须建立一定数量的储气库。中东部地区缺乏含水层及枯竭气藏构造，只有选取盐岩地层作为储气库选址。我国盐岩具有薄互层构造，在腔体顶部具有很厚的盐岩-泥岩互层，这种盐层作为盐岩储气库的顶板的封闭性能，是值得深入研究和探索的重要课题，事关储气库的长期密闭性。.围绕薄互层盐岩储气库顶板封闭性机制这一关键科学问题，本项目拟开展的研究内容包括：顶板薄互层盐岩的细观组构特征及物性封闭机理，高杂质盐岩渗透演化机理及扩容特征，顶板交界面的破坏控制判据及局部渗漏通道形成的判定条件，渗透模型、扩容准则及破损判据嵌入数值仿真软件、并结合现场测试对其验证、修正和应用。.通过项目研究得出的重要结果包括：通过系统的封闭指标测试、细观实验与孔渗测试等研究，揭示了盐岩地层盖层的物性与密闭性封闭机理；基于非稳态、稳态渗透-力学耦合实验，探明了不同试样类型的渗透演化规律与扩容规律研究；基于渗透试验与理论，研究了运行30年的腔体及顶板密闭性；基于顶板盐层破损及垮塌的事故分析，研究了顶板垮塌对密闭性的影响特征，并提出相应的对策。.关键数据包括：顶板泥岩盖层的突破压力范围为2.94-66.43MPa，平均值为27.279MPa，参考油气盖层封闭指标属于“很好”的级别；泥岩盖层的渗透率在10-18~10-20m2量级，属于极低渗透的介质；界面的渗透率在10-17~10-18m2，是最易渗透的部位，但仍然属于低渗透介质。夹层和界面是渗透的主要通道。.探明了顶板薄互层盐岩的封闭性机制问题，研究了泥岩夹层渗透性对腔体顶板密闭性的问题，研究了顶板局部垮塌对密闭性及气体渗漏的影响，提出了相应对策。