Estimation of Sedimentary Rock Porosity Using a Digital Image Analysis

Pore space characterisation is important in assessing the strength and hydraulic characteristics of rock. This paper proposes a new relationship to estimate the porosity of natural rocks using the data from a scanning electron microscope (SEM) and a pore and crack analysis system (PCAS). The obtained results were compared with the data obtained from a series of conventional mercury intrusion porosimetry (MIP) experiments. Three different rocks, namely siltstone, sandstone, and coal, collected from a depth below 400 m, were investigated in this study. The results indicated that the proposed method of digital analysis could accurately identify the pore size and porosity values, which were in agreement with the experimental data. The relationship between the two-dimensional porosity estimated from the digital analysis and the three-dimensional porosity obtained from laboratory experiments was established. A few limitations on the use of the proposed method have also been identified and discussed.