Pore pressure prediction in shales undergoing compaction, including both mechanical and chemical processes, is customarily related to the mechanism referred to disequilibrium compaction. However, even when this mechanism is established and the normal compaction trend in sonic velocity, as a proxy for shale porosity, is well constrained, the pore pressure prediction may be in error because of the lithological variation in shale composition. The presence of solid organic matter in excess amounts in shale formations that have never been exposed to the pressure–temperature conditions in the oil window is an example of these lithological effects, causing marked overprediction of pore pressure even in thermally immature mudrocks. This necessitates implementation of bulk density and sonic velocity log corrections in organic‐rich shales prior to performing standard pore pressure prediction workflows. In this paper, it is shown how these corrections can be made and the outcomes of the pore pressure prediction can be dramatically improved by using combination of rock physics models relating bulk density to total organic carbon and P‐wave velocity to bulk density in organic‐rich and conventional shales, respectively. To illustrate the workflow, a case study from a well drilled through the Kimmeridge Clay Formation in the North Sea, a well‐recognized source rock with total organic carbon content in the 2%–12% range and significant variation in clay content from 25% to 60%, both of which strongly affect the most commonly utilized log responses recorded in this formation. Using this old but data‐rich well, the importance of accounting for both total organic carbon and clay content variations in pore pressure prediction is demonstrated. It is also recognized that this workflow does not immediately apply to unconventional shale plays, where the pore pressure generation mechanisms are more complex and cannot be solely ascribed to compaction disequilibrium.

中文翻译：

---

校正总有机碳的密度/声波测井，以减少孔隙压力预测的不确定性

通常，在经历压实作用的页岩中，包括机械过程和化学过程中的孔隙压力预测通常与称为不平衡压实的机理有关。但是，即使建立了这种机理，并且很好地限制了声速的正常压实趋势（作为页岩孔隙度的替代指标），但由于页岩组成的岩性变化，孔隙压力预测可能仍会出错。这些岩性影响的一个例子就是从未暴露于油窗压力-温度条件的页岩地层中存在过量的固体有机物，即使在热不成熟的泥岩中，也导致对孔隙压力的明显预测。因此，在执行标准孔隙压力预测工作流程之前，必须在富含有机物的页岩中实施体积密度和声速测井校正。本文显示了如何通过结合岩石物理模型将体积密度与总有机碳相关以及P波速度与有机碳中的体积密度相关联来进行这些校正以及显着改善孔隙压力预测的结果。富含页岩和常规页岩。为了说明工作流程，以北海的金梅里奇粘土层钻探的一桩井为例，这是公认的烃源岩，其有机碳总量在2％–12％范围内，而粘土含量从25％显着变化到60％，这两个因素都会强烈影响以这种形式记录的最常用的测井响应。使用这个古老但数据丰富的井，证明了在孔隙压力预测中考虑总有机碳和粘土含量变化的重要性。还应认识到，该工作流程并不立即适用于非常规的页岩气层，在该页岩层中，孔隙压力的产生机制更为复杂，不能仅归因于压实不平衡。