Abstract

24 sandstone samples from Singrauli coal measure basin of lower Gondwana system (M P) having a range of porosities (~4 % to 35 %), apparent densities (1.69 g/cc to 2.54 g/cc; standard deviation from the mean is 0.2 g/cc), and true densities (2.51 g/cc to 2.66 g/cc; standard deviation from the mean is 0.04 g/cc) were studied in the laboratory. Observed apparent densities were plotted against the observed true densities in the same scale, range and units on both the axes. It was found that the data points falling on the line of unit slope passing through the origin correspond to the zero porosity values. This line of unit slope was named as the zero line. By further analysis of the laboratory-observed data and their spread in the apparent versus true density plot, the region perpendicularly away and under the zero line was divided into 15 equal strips, each representing 5 % porosity value. In this way, a grid was prepared in which true density, apparent density and porosity were varying in (x), (y) and diagonal to (x-y) directions respectively.