密度测井和中子测井的相关性及其在识别天然气层中的应用

THE CORRELATIVITY OF DENSITY LOG AND NEUTRON LOG AND ITS APPLICATION IN IDENTIFYING GAS FORMATIONS

伽马射线与地层介质的康普顿（Ｃｏｍｐｔｏｎ）效应是密度测井的理论基础，介质对伽马射线的康普顿吸收系数取决于介质的原子核性质及其体积密度．（超热或热）中子测井主要反映地层介质的减速性质，而后者主要取决于介质的含氢量．介质含氢量是由介质的组分及其体积密度决定的．本文从上述两种测井方法的测量原理出发，从理论上证明了这两种测井方法并非两种互相独立的测量手段．对于含油气盆地常见沉积岩石及矿物，两种测井测量结果具有相关性．这一结论为密度、中子测井方法组合地质应用提供了理论依据，利用密度－中子测井的相关性可有效地识别轻质油气层特别是天然气层．实例表明，无论水层还是油气层，两种测井曲线均具有良好的相关性．利用这种相关性明显改善了识别天然气层和划分油－气界面的精度．

The formation density logging is based on the Compton scattering effect of gamma rays and matter in the formation. The scattering effect depends on the neuclear characteristics and the bulk density of the matter. The neutron log measures the as yet uncaptured thermal neutron density which directly relates to the hydrogen content of the formation. According to the measuring equations of the two logs, this paper demonstrated theoretically that density log is not independent of neutron log.The two logs do relate for most sedimentary rocks and minerals encountered in hydrocarbon bearing basins. The good correlation between density log and neutron log results in broad applications in formation evaluation, such as determination of porosity, identification of lithology, especially in identification of natural gas formation and of contact of oil and gas.The field example showed that the excellent correlation between the two logs in all formations including oil,gas,and water layers.The application of the correlativity much improved the determination of the contact of oil and gas.