Pore volume analysis of gas shale samples using 3-D X-ray micro tomography

Understanding the porosity of gas shale is of great importance in many applications such as for enhanced recovery in gas reservoir. The first step for understanding the above properties is the precise quantification of the structure of the porous media. The structure may be characterised using traditional surface area measurement or mercury porosimetry for pore size analysis. However, these methods would provide data rather on pore sizes rather than their structures and configuration within low permeable samples. Modern 3D and non-destructive imaging techniques such as x-ray microtomography (XMT) provides a more convenient and intuitive alternative technique to scanning electron microscopy. The importance of quantitative pore structure characterization in understanding shale reservoir behaviors and lack of measurement techniques are the two main motivation factors behind this research. In this research three-dimensional x-ray micro tomography (XMT) imaging techniques were used to carry out a three-dimensional pore volume analysis of shale samples based on pores size, structure, geometry and orientation. Two samples with different properties (mainly in mercury intrusion porosity, MIP) were tested. It was found that the overall micro porosity obtained from XMT is about 0.7% and 0.3% for sample 1 and 2 respectively and significantly less than those of MIP. Both samples have very close structure orientation and geometry of the pores.