Overpressure generation by load transfer following shale framework weakening due to smectite diagenesis
Overpressure generation by load transfer following shale framework weakening due to smectite diagenesis
复制标题
DOI：
10.1111/j.1468-8123.2011.00350.x
复制
发表时间：
2011-11
期刊：
影响因子：
1.7
通讯作者：
R. Lahann;R. Swarbrick
中科院分区：
文献类型：
--
作者：
R. Lahann;R. Swarbrick
盆地模型研究，解决了蒙脱石转化为伊利石作为墨西哥湾超压源的重要性，主要依赖于一个单一的页岩压实模型和处理的蒙脱石反应作为唯一的流体源项。最近的流体压力解释和页岩岩石学研究表明，结合水转化为移动的水，承载颗粒的溶解，以及增加的优选取向改变了页岩的压实性能。这导致有效应力和流体压力的实质性变化。由此产生的流体压力可能比基于浅层压实趋势的模型解释的压力高1500-3000 psi。页岩成岩作用改变了页岩中承载颗粒的矿物学、体积和取向以及束缚水的体积。这个过程创建了一个更弱（更易理解）的颗粒框架。当这些变化发生而没有流体从页岩中输出时，一些应力从颗粒转移到流体上。在墨西哥湾陆架威尔斯井中观察到的页岩密度和计算出的有效应力之间的关系证实了页岩性质随深度的这些变化。此外，密度有效应力的变化不能解释流体膨胀或流体源过程或成岩前压实，但在埋藏过程中的页岩矿物学，纹理和压实性能的动态成岩修改是一致的。这些研究结果支持将压实特性的成岩改性作为流体压力解释过程的一部分。
Basin model studies which have addressed the importance of smectite conversion to illite as a source of overpressure in the Gulf of Mexico have principally relied on a single-shale compaction model and treated the smectite reaction as only a fluid-source term. Recent fluid pressure interpretation and shale petrology studies indicate that conversion of bound water to mobile water, dissolution of load-bearing grains, and increased preferred orientation change the compaction properties of the shale. This results in substantial changes in effective stress and fluid pressure. The resulting fluid pressure can be 1500–3000 psi higher than pressures interpreted from models based on shallow compaction trends. Shale diagenesis changes the mineralogy, volume, and orientation of the load-bearing grains in the shale as well as the volume of bound water. This process creates a weaker (more compactable) grain framework. When these changes occur without fluid export from the shale, some of the stress is transferred from the grains onto the fluid. Observed relationships between shale density and calculated effective stress in Gulf of Mexico shelf wells confirm these changes in shale properties with depth. Further, the density–effective stress changes cannot be explained by fluid-expansion or fluid-source processes or by prediagenesis compaction, but are consistent with a dynamic diagenetic modification of the shale mineralogy, texture, and compaction properties during burial. These findings support the incorporation of diagenetic modification of compaction properties as part of the fluid pressure interpretation process.