Characterization of pore and grain size distributions in porous geological samples – An image processing workflow

Hossein Safari,Bruce J Balcom,Armin Afrough

doi:10.1016/j.cageo.2021.104895

Abstract

An image processing workflow is presented for the characterization of pore and grain size distributions in porous geological samples from X-ray microcomputed tomography (μCT) and scanning electron microscopy (SEM) images. The pore and grain size distributions of five sandstone samples including Berea, Buff Berea, Nugget, Castlegate, and Bentheimer, and one carbonate sample, Indiana limestone, are extracted using the proposed workflow. Two-dimensional size distributions acquired from SEM images were found to be biased toward smaller sizes misrepresenting the actual 3D distributions. Stereological techniques unfolded the measured 2D size distributions from SEM images to 3D distributions comparable with μCT results. While larger pores and grains can easily be detected from μCT and SEM images, the quantification of small-scale heterogeneities is severely influenced by their limits of resolution. We show that microstructural details resolved by SEM can significantly impact the pore and grain size distributions in sandstone and carbonate rock samples. For example, SEM-resolved microporosities in Indiana limestone result in bimodal distributions of pore and grain sizes, whereas μCT observations exhibit unimodal distributions. The acquired images and processed results are openly available and may be used by researchers investigating image processing, magnetic resonance relaxation or fluid flow simulations in natural rocks. The proposed methodology can be implemented to process μCT and SEM images of natural rocks as well as other types of porous materials.

Highlights

IntroductionThe characterization of pore and particle/crystal/grain size distri butions in porous materials has a broad spectrum of applications in geosciences (Berger et al, 2011; Ghasemi et al, 2018; Roostaei et al, 2020; Srisutthiyakorn and Mavko, 2019), sedimentology (Gaafar et al, 2014; Palavecino et al, 2018), petroleum engineering (Burdine, 1953; Luo et al, 2019; Song et al, 2019, 2019b; Tian et al, 2019), chemical engineering (Bardestani et al, 2019; Kenvin et al, 2015; Occelli et al, 2003), and biomedical sciences (Bagherzadeh et al, 2013; Bartos et al, 2018; Udenni Gunathilake et al, 2017)
We have shown the application of a proposed image processing workflow for the extraction of pore and grain size distributions from Xray microcomputed tomography and scanning electron microscopy im ages in five different sandstones and one carbonate sample
While it was difficult to distinguish between the mineral phases in rock samples from μCT images, clay minerals in sandstones, scanning electron microscopy (SEM) images pro vided a sufficient contrast to observe different minerals from 2D crosssections

Summary

Introduction

The characterization of pore and particle/crystal/grain size distri butions in porous materials has a broad spectrum of applications in geosciences (Berger et al, 2011; Ghasemi et al, 2018; Roostaei et al, 2020; Srisutthiyakorn and Mavko, 2019), sedimentology (Gaafar et al, 2014; Palavecino et al, 2018), petroleum engineering (Burdine, 1953; Luo et al, 2019; Song et al, 2019, 2019b; Tian et al, 2019), chemical engineering (Bardestani et al, 2019; Kenvin et al, 2015; Occelli et al, 2003), and biomedical sciences (Bagherzadeh et al, 2013; Bartos et al, 2018; Udenni Gunathilake et al, 2017). Crystal and grain size distri butions are used to quantify the texture of solid rocks, characterize sediments based on their depositional environments, and control sand production in wellbores drilled in unconsolidated and consolidated sandstone rocks (Ghasemi et al, 2018; Higgins, 2000; Srisutthiyakorn and Mavko, 2019)

Methods

Results

Conclusion