四川盆地涪陵地区压力-应力耦合下的页岩超压保存

Gas-rich shales are generally characterized by varying degrees of overpressure, indicating that the preservation of overpressure has significant impacts on the enrichment of shale gas. Only a qualitative connection between the overpressure preservation in shale and the tectonic deformations is incomplete, since the overpressure preservation was inherently controlled by the coupling between pore pressure and stress. Therefore, in order to uncover the correlative mechanisms of the overpressure preservation controlled by pressure-stress coupling and the gas enrichment in shale, a systematic research is essential. Integrating the evolution of tectonic stress and the attributes of multi-period natural-fractures to determine the pressure-stress coupling ratio of various regions in different geologic periods. Then, a systematic assessment on the evolution of maximum sustainable overpressure that controlled by the pressure-stress coupling ratio of various regions in different geologic periods. Additionally, the pressure-stress coupling ratios also would be calculated by using the poroelastic theory and the mechanics properties of rocks in different geologic periods. A comparison between the calculative and real ratios of pressure-stress coupling would be conducted to investigate the control factors that induce changings of the pressure-stress coupling ratio or the maximum sustainable overpressure. Finally, a model would be established to illustrate the correlative of the overpressure preservation and the gas enrichment in shales.

富气页岩普遍含有不同程度的超压，表明页岩超压保存对于页岩气富集具有重要影响。目前，页岩超压保存与构造改造的定性关联存在不足，实际上，超压保存是压力-应力耦合作用的结果。针对压-应耦合下的页岩超压保存和页岩气富集、贫化这一科学问题，综合区域应力场演化和页岩天然裂缝系统时空发育规律及相应属性（期次，产状、开启压力、时间），实际揭示不同地区在不同演化阶段的压-应耦合关系和超压保存能力；基于不同演化阶段各类页岩的固有力学属性变化规律，理论计算不同地区在不同演化阶段的压-应耦合关系，对比耦合关系理论值和实际值，深化复杂地质过程中多因素复合作用对压-应耦合关系的影响，明确超压保存能力、页岩气富集程度时空变化规律和相关主控因素，最终指导海相页岩气勘探，丰富压-应耦合理论。

富气页岩普遍含有不同程度的超压，且超压保存对于页岩气富集具有重要意义。复杂构造带内多尺度变形过程中压力-应力存在耦合调整。围绕压-应耦合下的页岩超压保存和页岩气富集、贫化这一核心问题，通过多学科交叉、静态多层次解析与动态正、反演数值模拟相结合，开展了本次研究。结果表明：齐岳山断裂带核部相对于围岩区具有更高的水平主应力量级；龙马溪组页岩岩心存在燕山期、喜山期两幕古应力记忆；临近断裂核部，五峰-龙马溪组页岩层内裂缝系统丰度更高，而远离断裂核部，顶底板裂缝丰度更高；五峰-龙马溪组页岩力学性质与矿物组分、热演化过程、环境条件复杂关联；深埋阶段的热演化生烃是五峰-龙马溪组页岩主要的超压成因机制。在构造抬升阶段，流体压力的绝对量级逐步降低，但压力系系数逐步增大；早白垩纪末大幅度挤压隆升后，可容纳超压极限降低，失去部分页岩气保存能力；中新世以来的挤压-走滑转换调整，可容纳超压极限再次降低，导致深埋页岩失去部分页岩气保存能力。