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Novel 3D centimetre-to nano-scale quantification of an organic-rich mudstone: the Carboniferous Bowland Shale, Northern England

DOI: 10.1016/j.marpetgeo.2016.02.008 DOI Help

Authors: Lin Ma (University of Manchester) , Kevin Taylor (University of Manchester) , Peter D Lee (University of Manchester) , Katherine Dobson (University of Manchester) , Patrick Dowey (University of Manchester) , Loic Courtois (University of Manchester)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Marine And Petroleum Geology , VOL 72 , PAGES 193–205

State: Published (Approved)
Published: April 2016

Open Access Open Access

Abstract: X-ray computed tomography and serial block face scanning electron microscopy imaging techniques were used to produce 3D images with a resolution spanning three orders of magnitude from ∼7.7 μm to 7 nm for one typical Bowland Shale sample from Northern England, identified as the largest potential shale gas reservoir in the UK. These images were used to quantitatively assess the size, geometry and connectivity of pores and organic matter. The data revealed four types of porosity: intra-organic pores, organic interface pores, intra- and inter-mineral pores. Pore sizes are bimodal, with peaks at 0.2 μm and 0.04 μm corresponding to pores located at organic–mineral interfaces and within organic matter, respectively. These pore-size distributions were validated by nitrogen adsorption data. The multi-scale imaging of the four pore types shows that there is no connected visible porosity at these scales with equivalent diameter of 20 nm or larger in this sample. However, organic matter and clay minerals are connected and so the meso porosity (<20 nm) within these phases provides possible diffusion transport pathways for gas. This work confirms multi-scale 3D imaging as a powerful quantification method for shale reservoir characterisation allowing the representative volumes of pores, organic and mineral phases to be defined to model shale systems. The absence of connected porosity at scales greater than 20 nm indicates the likely importance of the organic matter network, and associated smaller-scale pores, in controlling hydrocarbon transport. . The application of these techniques to shale gas plays more widely should lead to a greater understanding of properties in the low permeability systems.

Journal Keywords: Multi-scale imaging; Bowland shale; X-ray tomography; Three-dimensional electron microscopy (3D-EM); Organic matter; Porosity; Shale gas

Subject Areas: Earth Science
Collaborations: Diamond Manchester

Instruments: I13-2-Diamond Manchester Imaging