ESTIMATION OF POROSITY BY SONIC LOG USING DIFFERENT EMPIRICAL RELATIONSHIPS

Abstract

Several empirical relationships relating sonic transit time and porosity have been proposed by different workers from time to time. Each of these relations is applicable to a specific field condition and has its own limitations and deficiencies. The main objective of present work is to overcome some of these limitations. An attempt has been made to develop an optimistic method which involves a suitable integration of velocity transform equation to calculate porosity from gamma ray log and sonic log using real log data. A C++ program has been written to accomplish this task. This new optimistic approach gives superior porosity values with smaller errors. This is expected to enable a log analyst to use it as a quick check method in a recent exploratory well before the decision to carry out complete logging is done. Also this method can be used in wide range of lithologies (clean-sandlshaly formations), especially for older wells that lack neutrondensity crossover or where core measurements are absent. In addition to being a simple method, it also treats the shale effect as a correction term from a specific part of formation and not from the entire well as was done in the earlier approach. Successful application to real field data basin has also been demonstrated