岩性密度测井可同时测量地层体积密度和有效光电吸收截面指数。该指数与地层中各种元素的原子序数有关,因此可以用作地层岩性的指示参数。岩性密度测井方法已成功地用于各种岩性条件,对于复杂岩性的含油气层的评价起了重要的作用。在复杂岩性而且存在轻烃的条件下,常用的中子和密度测井资料就显得不充分,呈现多解现象。此时,上述的有效光电吸收截面指数就更有特殊的意义, 一、原理伽玛射线与物质的相互作用有三种效应:康普顿散射,光电效应和电子对效应。在常用伽玛源所放射的伽玛射线的能量范围内,只需考虑前两种效应。关于康普顿散射, Lithologic density logging can simultaneously measure formation bulk density and effective photoelectric absorption cross section index. The index is related to the atomic number of various elements in the formation and can therefore be used as an indicator of formation lithology. Lithologic density logging methods have been successfully applied to various lithological conditions and played an important role in the evaluation of oil and gas bearing formations with complex lithology. In the complex lithology and the presence of light hydrocarbons, the commonly used neutron and density logging data appear inadequate, showing a multi-solution phenomenon. At this point, the above-mentioned effective photoelectric absorption cross-section index has more special significance, First, the principle of gamma ray and the material interaction has three effects: Compton scattering, photoelectric effect and electron pair effect. Within the energy range of gamma rays emitted by commonly used gamma sources, only the first two effects need to be considered. About Compton scattering,