Pore pressure prediction from well logs: Methods, modifications, and new approaches
Pore pressure prediction from well logs: Methods, modifications, and new approaches
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DOI：
10.1016/j.earscirev.2011.06.001
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发表时间：
2011-09
影响因子：
12.1
通讯作者：
Jincai Zhang
中科院分区：
文献类型：
--
作者：
Jincai Zhang
大多数深层沉积地层中的孔隙压力不是静水压力，而是超压，甚至升高到静水压力的两倍以上。如果在钻井前不能准确预测异常压力，可能会发生井喷和泥火山等灾难性事件。介绍了水力连通地层的孔隙压力计算方法。对裂缝梯度预测方法进行了综述，提出了最小和最大破裂压力。然后，本文综述了利用测井资料预测异常孔隙压力的常用经验方法。伊顿的电阻率和声波方法，然后采用深度相关的正常压实方程在地下地层孔隙压力预测。调整后的方法提供了一种更容易的方法来处理正常的压实趋势线。除经验方法外，理论孔隙压力模拟是理解异常压力产生机理的基础。基于超压产生的主要机制--压实不平衡和有效应力-孔隙度-压实理论，提出了孔隙度-压力理论模型。因此，孔隙压力预测从纵波速度和声波时差获得使用新的理论模型。深水油井威尔斯的案例研究说明了如何改进沉积地层孔隙压力预测。
Pore pressures in most deep sedimentary formations are not hydrostatic; instead they are overpressured and elevated even to more than double of the hydrostatic pressure. If the abnormal pressures are not accurately predicted prior to drilling, catastrophic incidents, such as well blowouts and mud volcanoes, may take place. Pore pressure calculation in a hydraulically-connected formation is introduced. Fracture gradient prediction methods are reviewed, and the minimum and maximum fracture pressures are proposed. The commonly used empirical methods for abnormal pore pressure prediction from well logs are then reviewed in this paper. Eaton's resistivity and sonic methods are then adapted using depth-dependent normal compaction equations for pore pressure prediction in subsurface formations. The adapted methods provide a much easier way to handle normal compaction trendlines. In addition to the empirical methods, the theoretical pore pressure modeling is the fundamental to understand the mechanism of the abnormal pressure generation. A theoretical pore pressure-porosity model is proposed based on the primary overpressure generation mechanism — compaction disequilibrium and effective stress-porosity-compaction theory. Accordingly, pore pressure predictions from compressional velocity and sonic transit time are obtained using the new theoretical model. Case studies in deepwater oil wells illustrate how to improve pore pressure prediction in sedimentary formations.