Analysis of compressional and shear-wave sonic logs in seven organic-rich shale reservoirs exhibiting a wide range of velocities, total organic content, thermal maturity, fluid compressibility and mineral composition indicates that compressional-wave velocity is a strong predictor of shear-wave velocity as is the case for conventional reservoirs. Excluding data with high water saturations, a simple linear relationship is found between the compressional and shear-wave velocities in shale reservoirs in accordance with laboratory measurements. The relationship can be further refined for prediction purposes by local calibration or with a linear correction for total organic content. Correcting for compositional variation and fluid effects requires more complex treatment. An empirical rock physics model that explicitly incorporates these effects results in high accuracy (0.2% average mean error) in shear-wave velocity estimation for the entire data set. The model also exhibits good precision with mean absolute error of 2%. This is significantly better than what is achieved by rock physics models that do not explicitly consider fluid properties. These results are obtained without local calibration and without requiring correction for thermal maturity, degree of lithification or the shape or distribution of the solid organic matter. Explicit consideration of mineral composition, fluid substitution effects and amount of solid organic matter was necessary in this formulation to achieve this high average prediction accuracy with near zero bias as well as good precision across all formations and without local calibration. The successful use of Gassmann's equations in this algorithm suggests that errors in shear-wave velocity prediction in shale reservoirs due to violation of the assumptions underlying these equations are either small or self-compensating.

中文翻译：

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非常规页岩储层剪切波速度的估算

对七个富有机质页岩储层的纵波和横波声波测井分析表明，这些油藏具有广泛的速度、总有机质含量、热成熟度、流体压缩性和矿物成分，表明纵波速度是横波速度的有力预测因子与常规水库的情况一样。排除具有高含水饱和度的数据，根据实验室测量发现页岩储层中的压缩波速度和剪切波速度之间存在简单的线性关系。为了预测目的，可以通过局部校准或对总有机物含量进行线性校正来进一步细化该关系。校正成分变化和流体效应需要更复杂的处理。明确包含这些影响的经验岩石物理模型在整个数据集的剪切波速度估计中具有高精度（0.2% 平均平均误差）。该模型还表现出良好的精度，平均绝对误差为 2%。这明显优于未明确考虑流体特性的岩石物理模型。这些结果是在没有局部校准的情况下获得的，也不需要对热成熟度、岩化程度或固体有机物的形状或分布进行校正。明确考虑矿物成分，在该公式中，流体置换效应和固体有机物的数量是必要的，以实现这种高平均预测精度，接近零偏差以及所有地层的良好精度，无需局部校准。Gassmann 方程在该算法中的成功使用表明，由于违反这些方程所依据的假设而导致的页岩储层剪切波速度预测误差很小或可以自我补偿。