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确定煤层原地基含气量是评价煤层气资源中非常关键的一步。目前认为,煤层含气量与煤层气中的有机成分和无机成分这两个独立成分的相对丰度具有函数关系。在有些煤田内有机成分几乎不变,而无机成分可能在横向和垂向上变化显著。因此,从理论上讲测井响应能够反映煤层气中无机成分的变化,并通过测井响应有效评价煤层含气量。然而,目前通用的评价方法是密度测井,效率比较低,不是将声波测井、光电吸收指数、伽马测井等一起应用,实际上这几种测井响应也可反映煤层中无机成分的变化。本文提到的新方法,主要是用上述的三种测井方法联合密度测井推导每一个煤心样品的复合数值C。不同深度的C值曲线与实测煤层含气量具有较好的相关性。实践证明C值曲线和煤心化验测得的含气量曲线吻合得很好,它们之间相差常数K。而K值的确定只取决于煤层的性质。因此,评价一定深度煤层含气量只需简单地用C值加上K值。印度2个不同的煤田已经使用了这种方法。试验证明,综合应用多种测井响应推导的结果是合理而精确的。这一技术为不同性质的煤田计算其含气量提供了可靠的方法。
Determining the gas content of the original coalbed is a very crucial step in the evaluation of CBM resources. At present, it is considered that the coalbed gas content has a functional relationship with the relative abundance of two independent components, organic and inorganic, in coalbed methane. In some coalfields, the organic components are almost unchanged while the inorganic components may vary significantly in both horizontal and vertical directions. Therefore, in theory, the well logging response can reflect the change of inorganic components in coalbed methane and effectively evaluate the coalbed gas content through well logging response. However, the current common evaluation method is density logging, which is inefficient. It is not applied to sonic logging, photoelectric absorption index, gamma logging and the like. In fact, these well logging responses may also reflect the composition of inorganic components in coal seams Variety. The new method mentioned in this article mainly uses the above three logging methods combined with density logging to derive the composite value C for each coal core sample. Different depth of the C value curve and the measured coal content has a good correlation. Practice has proved that the C value curve and the coal content of the gas measured curve fitting well, with a constant K between them. The K value is determined only by the nature of the coal seam. Therefore, the evaluation of a certain depth of coal gas content simply by C value plus K value. Two different coalfields in India already use this method. The test proves that it is reasonable and accurate to synthesize the results derived from various logging responses. This technique provides a reliable method for calculating the gas content of different types of coal fields.