The effect of clay distribution on the elastic properties of sandstones
The effect of clay distribution on the elastic properties of sandstones
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DOI：
10.1046/j.1365-2478.2001.00230.x
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发表时间：
2001-01
影响因子：
2.6
通讯作者：
M. Sams;M. Andrea
中科院分区：
文献类型：
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作者：
M. Sams;M. Andrea
砂岩中粘土的形状和位置对岩石的P波和S波速度有很大的影响。它们还对储层性质以及从地震数据和测井曲线对这些性质的解释产生很大影响。不同分布的粘土-结构，层状和分散粘土-的数值模型可以导致对这些影响的理解。位于石英颗粒之间的粘土，结构性粘土，将降低岩石的P波和S波速度。如果粘土颗粒排列或形成层，则垂直于排列的速度将进一步减小。随着粘土含量的增加，横波速度比纵波速度下降得更快，因此泊松比将随着速度的降低而增加。这些影响对于压实砂岩更为明显。由于密度效应和孔隙流体硬化的竞争影响，位于孔隙空间中的少量粘土对P波速度的影响很小。由于密度效应，S波速度将降低，因此泊松比将增加。当有足够的粘土来桥接石英颗粒之间的间隙时，P波和S波速度迅速上升，泊松比降低。这些影响在欠压实砂岩中更为明显。当考虑到粘土材料的固有各向异性时，这些一般结果仅略有修改。数值模型表明，P波和S波速度之间存在强烈的、几乎线性的关系，几乎与粘土分布无关。基于经验关系，横波速度可以从纵波速度相当准确地预测。然而，这并没有提供岩石的弹性和岩石物理性质之间的任何联系。数值模拟提供了这种联系，但需要包括粘土分布和各向异性，以提供一个模型，是一致的弹性和岩石物理性质。例如，如果忽略粘土分布，则根据P波或S波数据预测孔隙度可能会导致较大的误差。根据P波和S波速度估计粘土分布需要对孔隙度和粘土体积进行良好的估计，并通过岩心或岩屑的岩相分析进行验证。对于一个真实的数据示例，弹性特性的数值模型表明，根据P波和S波速度测井数据的匹配（使用基于测井的粘土体积和孔隙度估计值），分散粘土在河流砂中占主导地位。这与其他测井数据的解释一致。
The shape and location of clay within sandstones have a large impact on the P‐wave and S‐wave velocities of the rock. They also have a large effect on reservoir properties and the interpretation of those properties from seismic data and well logs. Numerical models of different distributions of clay – structural, laminar and dispersed clay – can lead to an understanding of these effects. Clay which is located between quartz grains, structural clay, will reduce the P‐wave and S‐wave velocities of the rock. If the clay particles become aligned or form layers, the velocities perpendicular to the alignment will be reduced further. S‐wave velocities decrease more rapidly than P‐wave velocities with increasing clay content, and therefore Poisson's ratios will increase as the velocities decrease. These effects are more pronounced for compacted sandstones. Small amounts of clay that are located in the pore space will have little effect on the P‐wave velocity due to the competing influence of the density effect and pore‐fluid stiffening. The S‐wave velocity will decrease due to the density effect and thus the Poisson's ratio will increase. When there is sufficient clay to bridge the gaps between the quartz grains, P‐wave and S‐wave velocities rise rapidly and the Poisson's ratios decrease. These effects are more pronounced for under‐compacted sandstones. These general results are only slightly modified when the intrinsic anisotropy of the clay material is taken into account. Numerical models indicate that there is a strong, nearly linear relationship between P‐wave and S‐wave velocity which is almost independent of clay distribution. S‐wave velocities can be predicted reasonably accurately from P‐wave velocities based on empirical relationships. However, this does not provide any connection between the elastic and petrophysical properties of the rocks. Numerical modelling offers this connection but requires the inclusion of clay distribution and anisotropy to provide a model that is consistent with both the elastic and petrophysical properties. If clay distribution is ignored, predicting porosities from P‐wave or S‐wave data, for example, can result in large errors. Estimation of the clay distribution from P‐wave and S‐wave velocities requires good estimates of the porosity and clay volume and verification from petrographic analyses of core or cuttings. For a real data example, numerical models of the elastic properties suggest the predominance of dispersed clay in a fluvial sand from matching P‐wave and S‐wave velocity well log data using log‐based estimates of the clay volume and porosity. This is consistent with an interpretation of other log data.