Multi-Scale 3-D Imaging and Quantification of Pores, Organic Matter and Minerals: An Example From the UK Carboniferous Bowland Shale

Abstract

Multi-scale 3D X-ray computed tomography (X-ray CT) and serial block face scanning electron microscopy (SBFSEM) imaging techniques crossing the range of scales from 7.7μm to 0.007μm were utilised to reveal the size, geometry and connectivity of pores, organic matter and minerals in a selected organic-rich sample of Carboniferous Bowland shale, which is considered to be the largest potential shale gas play in UK. The quantitative image analysis was compared to a number of physical and chemical analyses including nitrogen absorption, TOC, XRD, optical microscope and backscattered SEM to verify the accuracy and representative of 3D images. Imaging and quantification at five spatial voxel sizes of 7.7μm, 1.3 μm, 0.13 μm, 0.05 μm and 0.007μm shows that pore diameters are distributed around two main peaks of 0.2μm and 0.04μm, corresponding to organic matter interface pores and intra-organic matter pores respectively. A positive correlation was found between the shape factor and equivalent diameter of pores, and the pores are preferentially aligned to bedding. Over 75% of the organic matter forms a single interconnected structure. The visualization of nano-scale pores, micro-scale organic matter and meso-scale minerals and structures, as well as the consistency in mineral component percentages at all scales and the similar calculated size distributions in the overlapping parts of adjacent scales, further confirms multi-scale 3D imaging as a powerful quantification method in shale reservoir characterisation.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015