In the framework of a \({{\hbox {CO}}}_{2}\) storage feasibility study, we evaluate porosity and permeability of shale formations constituting the overburden of a hydrocarbon reservoir, where the gas is stored. These properties are required to perform fluid-flow simulations and analyze possible leakages from the reservoir to the surface. In this process, calibration with well logs is essential. Standard log-interpretation procedures on shales may induce errors, since the shale part is discarded due to its apparent negligible permeability compared to the clastic part. In this study, it is the “shale effect” that we consider by introducing its contribution to porosity and therefore to permeability, so that new expressions are developed to obtain porosity from density and traveltimes that consider this effect. Indeed, shales have non-zero porosity and finite permeability even if the flow rates are several orders of magnitude smaller than those in sandstones. Moreover, calibration does not mean to honour one single log profile but the interpretation should be compatible with all the profiles available. We obtain clay content, porosity and permeability from two wells offshore Malaysia using the linear and Stieber relations between gamma ray and shale volume. The results of using these relations are quite similar. However, the analysis shows that the density logs yield too small values of porosity. Instead, the sonic log gives a better estimate of porosity that honours the P-wave velocity. The verification is performed by using the Krief–Gassmann equations to obtain the P-wave velocity, either from the density-log or from sonic-log derived porosities. This is also confirmed by comparison to porosity obtained from the neutron log.

中文翻译：

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电缆测井中覆盖层的孔隙度和渗透率：以马来西亚近海为例

在\（{{\ hbox {CO}}} _ {2} \）的框架中储存可行性研究中，我们评估构成油气藏的上覆岩的页岩岩层的孔隙度和渗透率。这些属性是执行流体流动模拟和分析从储层到地面的可能泄漏所必需的。在此过程中，用测井仪校准是必不可少的。页岩的标准测井解释程序可能会引起误差，因为与碎屑岩相比，由于其表观渗透率可忽略不计，因此将其丢弃。在本研究中，我们通过介绍页岩对孔隙度的贡献以及由此对渗透率的贡献来考虑“页岩效应”，因此开发出新的表达式以从考虑该效应的密度和传播时间获得孔隙度。确实，页岩具有非零的孔隙度和有限的渗透率，即使流速比砂岩中的流速小几个数量级。而且，校准并不意味着要遵循一个单一的测井剖面，而是解释应与所有可用的剖面兼容。我们使用伽马射线与页岩体积之间的线性和斯蒂伯关系，从马来西亚近海的两口井中获得粘土含量，孔隙度和渗透率。使用这些关系的结果非常相似。但是，分析表明，密度测井的孔隙率值太小。取而代之的是，声波测井曲线可以更好地估计孔隙度，以符合P波速度。验证是通过使用Krief-Gassmann方程从密度测井或声波测井得出的孔隙度获得P波速度的。