Abstract
A comparative analysis of porosity is presented in the article. This was calculated from laboratory measurements and well logs for rocks from a selected region of the Carpathians. Analysis was performed for samples of sandstones, mudstones, shales and carbonates from four boreholes drilled in the Carpathian Foredeep region near Krakow, Poland. In laboratory measurements, porosity was assessed using two methods: helium pycnometry and nuclear magnetic resonance (NMR). Porosity from well logging was calculated from sonic profiling (SPHI). Cross-plots were used, which allowed for the assessment of the degree of correlation between the laboratory and well log data. The results obtained were analysed paying special attention to the relationship with geological structure. Based on the lithological criterion, the correlations turned out to be strong. The repeatability of the results obtained in different wells was verified. The results of the measurements are significant in relation to estimating porosity from well logs using laboratory data.
Highlights
The aim of the work is to compare the porosity of rocks from a selected region in the Carpathians calculated from laboratory methods and from well log SPHI
Three outlying samples were observed, with significant deviations from the regression line. They come from different boreholes (A-1 and A-2), and from different lithostratigraphic units (Neogene and Late Jurassic)
This is a confirmation of the trend observed for the entire set of samples – the value of the nuclear magnetic resonance (NMR) porosity is greater than that of the helium pycnometry
Summary
The aim of the work is to compare the porosity of rocks from a selected region in the Carpathians calculated from laboratory methods and from well log SPHI. An evaluation is made of the degree of correlation between the results of laboratory measurements and well logs, based on laboratory measurements of porosity and sonic well log SPHI. Well logs are a trustworthy source of data about physical parameters and variability measurements. They are usually performed at sampling intervals of 10-25 cm. Laboratory measurements on samples yield accurate results but have a point-based character, can only act as reference results in addition to well logs. It is necessary to underline that laboratory measurements can be performed in conditions that simulate those of the actual deposit (appropriate temperature and pressure)
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