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首页> 外文期刊>AAPG Bulletin >The velocity-deviation log: A tool to predict pore type and permeability trends in carbonate drill holes from sonic and porosity or density logs
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The velocity-deviation log: A tool to predict pore type and permeability trends in carbonate drill holes from sonic and porosity or density logs

机译：速度偏差测井：根据声波和孔隙率或密度测井预测碳酸盐钻孔的孔类型和渗透率趋势的工具

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The velocity-deviation log, which is calculated by combining the sonic log with the neutron-porosity or density log, provides a tool to obtain downhole information on the predominant pore type in carbonates. The log can be used to trace the downhole distribution of diagenetic processes and to estimate trends in permeability. Laboratory measurements on over 300 discrete carbonate samples reveal that sonic velocity is a function not only of total porosity, but also of the predominant pore type. In general, there is an inverse porosity-velocity correlation, but significant deviations occur from this relationship for certain pore types. Frame-forming pore types, such as moldic or intrafossil porosity result in significantly higher velocity values at equal total porosities than do pore types that are not embedded in a rigid rock frame, such as interparticle porosity or microporosity. The results of the laboratory measurements can be applied to expand interpretations of standard wireline-log data, as shown in this study on two drill holes through Neogene carbonates from the Great Bahama Bank. The velocity-deviation log is calculated by first converting porosity-log data to a synthetic velocity log using a time-average equation. The difference between the real sonic log and the synthetic sonic log can then be plotted as a velocity-deviation log. Because deviations are the result of the variability of velocity at a certain porosity, the deviation log reflects the different rock-physical signatures of the different pore types. Positive velocity deviations mark zones where velocity is higher than expected from the porosity values, such as zones where frame-forming pore types dominate. Zero deviations show intervals where the rock lacks a rigid frame, such as in carbonates with high interparticle porosity or microporosity Negative deviations mark zones in which sonic log velocities are unusually low caused, for instance, by a cavernous bore-hole wall, fracturing, or possibly by a high content of free gas. By tracing the velocity deviations continuously downhole, one can identify diagenetic zones that are characterized by these different pore types. In addition, this method can be used to observe permeability trends because pore types influence the permeability of the rock. [References: 32]
机译：通过将声波测井曲线与中子孔隙度或密度测井曲线相结合而计算出的速度偏差测井曲线为获得有关碳酸盐岩中主要孔隙类型的井下信息提供了一种工具。该测井曲线可用于追踪成岩过程的井下分布并估算渗透率的趋势。实验室对300多个离散碳酸盐样品的测量表明，声速不仅是总孔隙度的函数，而且还是主要孔隙类型的函数。通常，孔隙率与速度之间存在反比关系，但是对于某些孔隙类型，这种关系会产生明显的偏差。形成框架的孔隙类型（例如霉菌或化石孔隙）在相等的总孔隙率下比没有嵌入刚性岩石框架的孔隙类型（例如颗粒间孔隙或微孔隙）产生更高的速度值。实验室测量的结果可用于扩展对标准测井曲线数据的解释，如本研究通过大巴哈马银行的Neogene碳酸盐岩钻探的两个钻孔所示。通过首先使用时间平均方程将孔隙度日志数据转换为合成速度日志来计算速度偏差日志。然后，可以将实际声波测井曲线与合成声波测井曲线之间的差异绘制为速度偏差测井曲线。由于偏差是一定孔隙率下速度变化的结果，因此偏差记录反映了不同孔隙类型的不同岩石物理特征。正速度偏差表示速度高于孔隙率预期值的区域，例如，成帧孔隙类型占主导的区域。零偏差表示岩石缺乏刚性框架的时间间隔，例如在高颗粒间孔隙度或微孔隙度的碳酸盐岩中。可能是由于游离气体含量高。通过连续追踪井下的速度偏差，可以确定以这些不同孔隙类型为特征的成岩带。另外，由于孔隙类型会影响岩石的渗透率，因此该方法可用于观察渗透率趋势。 [参考：32]

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