Alejandro Arroyo Carrasco
Ulises Ricoy Saldana
Division de Evaluacion de Formaciones
Subdireccion de Tecnologia de la Exploracion
Instituto Mexicano del Petroleo
ABSTRACT
This paper’s main objective is to present theoretical and practical basis that will allow the design of digital filters to equalize different types of Logs. In particular the design of a filter to equalize logs of “gamma ray” and ‘spontaneous potential”.
Concepts of “signal theory”, such as Convolution, Correlation, Regression, Fourier Transformed, and Nyquist Theorem , are used to manipulate the logs previously digitated by computer algorithms.
Based on the convolution theorem, we can figure out a digital equalization filter between gamma rays and spontaneous potential logs, using the Fourier Inverse Transformed of frequence spectrum coefficient of both logs. This theoretical result was applied in two digitalized logs, using algorithms “ Rapid Fourier Transformed’and “ Maximum Enthrophie*s Method “ for the calculation of the respective spectrums and the results were compared. It be concluded that both procedures are satisfactory in determining the filters to equalize two different logs. Although the use of the maximum method offers better results.
Taking into account the Signal Theory, we can visualize different applications, which are of great interest in geophysical logs, like spectrum frequence analysis to establish frequencies of sedimentary events and automatize log correlation.