Evaluation of pore size spectrum of gas shale reservoirs using low pressure nitrogen adsorption, gas expansion and mercury porosimetry: A case study from the Perth and Canning Basins, Western Australia

Abstract

Gas shales have a complex pore structure. Mechanisms of gas storage in the gas shale pore system are in two ways, free gas and sorbed gas. The nanometer scaled pore systems of gas shale reservoirs have a prominent contribution for gas storage, especially for adsorbing gas onto their surfaces. In this study three different methods of low pressure nitrogen adsorption, mercury porosimetry and gas expansion were used for pore structure characterization of gas shales. Mercury porosimetry and gas expansion methods have been used for a long time in characterization of conventional reservoirs but low pressure nitrogen adsorption has been considered recently as a tool for gas shale evaluation. The studied gas shale samples are coming from the Perth and Canning Basins, Western Australia. Analyzing the results of case study shows that the Canning shale samples have the specific surface area and micro/mesopore volume around 13 m2/g and 1.4 cc/100 g, respectively, which are relatively higher than the same values for the Perth shale samples.Quantitative analysis of the obtained results clarifies the shape, size and pore volume of the studied gas shale samples. However analyzing the results shows that there is not any consistency between similar parameters like effective porosity or pore size distribution (PSD) extracted from these techniques; several explanations have been proposed for justification of this inconsistency. As well as the results of this study make it clear that each of the usual techniques applied for characterization of gas shale pore systems has some deficiencies and cannot be used alone for this purpose. Whereas, by combining the results of these methodologies pore size spectrum of gas shales can be determined in a more accurate way.