煤层气井内隔水层界面水窜形成演化过程与耦合作用机制

Controlling water channeling (water inrush) is the key to the efficient exploitation of coalbed methane (CBM). Well then, whether the confined water (bottom water) below aquifuge (coal seam floor) could migrate upward along cement-aquifuge interface (cementation plane between cement slurry and aquifuge), which leads CBM well to high water cut and even sudden water flooding? Based on the simulation experiment system of cement-aquifuge interface established independently, this project plans to use quantitative simulation experiments and modern chemical analysis to emphatically study the influence mechanisms of channeling medium characters (thickness and composition of mud cake, fracture of cement-aquifuge interface) and dynamic parameters (production pressure drop, bottom-water pressure) on the upward channeling of bottom water along cement-aquifuge interface. And the relational data between them are obtained. This will provide scientific basis for solution of water channeling problem, which exists universally in the exploitation of CBM reservoirs. Through this research, the quantitative relationship between these influence factors and upward channeling of bottom water along cement-aquifuge interface is clear. Based on the principles of mechanics and physical chemistry, the formation and evolution of channeling pathway of cement-aquifuge interface also is revealed. Meanwhile, a couping equation that depicts the upward channeling of bottom water is established, and its boundray conditions is determined. The couping equation is sloved by using numerical analysis method. And the coupling mechanism among the fracture of cement-aquifuge interface, mud cake, bottom water and dynamic is clarified. This will lay a theoretical and technical foundation for control of water channeling in the efficient exploitation of CBM reservoirs.

控制水窜(突水)是煤层气高效开采的关键，那么隔水层(底板)下部的承压水 (简称底水)会沿隔水层界面(隔水层岩体与水泥浆的胶结面)上窜而导致煤层气井高含水甚至爆性水淹吗？基于自主建立的隔水层界面仿真实验系统，拟用定量模拟实验和现代分析测试方法，着重研究窜流介质(泥饼厚度、泥饼组成、界面裂隙)和窜流动力(生产压差、底水压力)对底水沿隔水层界面上窜的影响机理，获得底水沿隔水层界面上窜与窜流介质和窜流动力的关系数据，为解决煤层气藏开采普遍存在的水窜难题提供科学依据。通过本项研究，明确底水沿隔水层界面上窜与窜流介质和窜流动力的定量关系，然后根据力学和化学原理，揭示隔水层界面水窜通道的形成与演化过程；同时，基于流固耦合理论，建立起刻画底水沿隔水层界面上窜的耦合方程，确定其边界条件，求解此耦合方程，进而阐明隔水层界面裂隙-泥饼-底水-动力耦合作用机制，为控制底水上窜提高煤层气开采效率奠定理论和技术基础。

控制水窜（突水）是煤层气高效开采的关键。通过本项目的研究，阐明了窜流介质和窜流动力对底水沿隔水层界面上窜的影响机理，揭示了底水沿隔水层界面上窜至储层的窜流通道形成和演化过程：实验研究结果表明，随着压差增大，隔水层界面水窜时间和通道贯通时间均越短，而当流量达到最大值后会迅速减小，减至最小值后又会略有升高，最后趋于平稳，且平缓段的流量与压差成正比关系，这与隔水层界面当量渗透率变化规律是一致的；隔水层界面水窜时间与泥饼厚度呈非线性关系，且随着泥饼厚度增加，隔水层界面水窜通道的贯通时间缩短，而隔水层界面当量渗透率的最小值和变化范围均呈对数式增长；基于提出的隔水层界面窜流系数（ξ）概念，将隔水层界面水窜形成演化过程可划分为三个阶段，即ξ＜1时水窜处于渗透阶段，1＜ξ＜1.12时水窜处于溶蚀阶段，ξ＞1.12时水窜处于致突阶段。在此基础上，理论推导并建立了底水沿隔水层界面上窜的耦合方程，进而分析了隔水层界面裂隙-泥饼-底水-动力耦合作用机制。同时，还基于自主建立的实验装置，验证了该此方程，结果表明方程计算值与实验值具有较好吻合度。这些研究成果可为控制底水上窜提高煤层气开采效率提供科学依据和技术基础。