Method for calculating photoelectric absorption cross-section index of stratum based on X-ray litho-density logging

Abstract

The invention discloses a method for calculating the photoelectric absorption cross-section index of a stratum based on X-ray litho-density logging. The method adopts an X-ray litho-density logging device and comprises the following steps that 1, X rays released by an X-ray source have a photoelectric effect and Compton scattering effect with the stratum, and are then received by a detector, the X-ray spectrum detected by the detector is taken as a basis to select and count low-energy windows and high-energy windows as NL and NH respectively, and then the photoelectric absorption cross-sectionindex U per volume of the stratum is calculated; and 2, the relation between the volume and the photoelectric absorption cross-section index is utilized, wherein Pe can be represented as Pe=U/rho e,and rho e represents the electron density index of the stratum. During X-ray litho-density logging, rho e serves as one of the measurement parameters, and can be regarded as a known number when the photoelectric absorption cross-section index is calculated. By means of the method, the influence of the density of the stratum on the measurement of the photoelectric absorption cross-section index Peof the stratum can be effectively eliminated, and the measurement accuracy is greatly improved.

Description

technical field [0001] The invention relates to a method for calculating formation photoelectric absorption section index based on X-ray lithology density logging, and belongs to the technical field of petroleum exploration. Background technique [0002] Lithology density logging is an important way to measure formation density and photoelectric absorption cross-section index (Pe). Lithology density logging includes 137 Cs lithology density logging and X-ray source lithology density logging, 137 Cs lithology density logging uses the chemical element cesium, which is radioactive. Although the X-rays in the X-ray source lithology density logging are also radioactive, they can be controlled by turning on and off the power, so as to reduce the harm to the human body as much as possible. Therefore, the application of X-ray source lithology density logging is more and more extensive. [0003] exist 137 In Cs lithology density logging, the detector receives the scattered γ pho...

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Problems solved by technology

However, for X-ray source lithology density logging, the count of the density window is not only affected by the formation density, but also by the photoelectric absorption cross-section index, so R is not only affected by the formation photoelectric absorption cross-section index, but also by the formation density However, when the ratio R is still used to calculate the photoelectric absorption cross-section index, due to the influence of the formation density, the error is relatively large

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