Pore-scale analyses of heterogeneity and representative elementary volume for unconventional shale rocks using statistical tools

Abstract

A statistical technique for the pore-scale analyses of heterogeneity and representative elemental volume (REV) in unconventional shale rocks is hereby presented. First, core samples were obtained from shale formations. The images were scanned using microcomputed tomography (micro-CT) machine at 6.7 lm resolution with voxels of 990 9 990 9 1000. These were then processed, digitised, thresholded, segmented and features captured using numerical algorithms. This allows the segmentation of each sample into four distinct morphological entities consisting of pores, organic matter, shale grains and minerals. In order to analyse the degree of heterogeneity, Eagle Ford parallel sample was further cropped into 96 subsamples. Descriptive statistical approach was then used to evaluate the existence of heterogeneity within the subsamples. Furthermore, the Eagle Ford parallel and perpendicular samples were analysed for volumetric entities representative of the petrophysical variable, porosity, using corner point cropping technique. The results of porosity REV for Eagle ford parallel and perpendicular indicated sample representation at 300 lm voxel edge. Both pore volume distribution and descriptive statistical analyses suggested that a wide variation of heterogeneity exists at this scale of investigation. Furthermore, this experiment allows for adequate extraction of necessary information and structural parameters for pore-scale modelling and simulation. Additional studies focusing on re-evaluation at higher resolution are recommended.

Composition Effect on the Pore Structure of Transitional Shale: A Case Study of the Permian Shanxi Formation in the Daning–Jixian Block at the Eastern Margin of the Ordos Basin

“…One method is to separate the kerogen from the shale by chemical solution and then characterize the quantitative influence of the OM on the pore structure (Kuila and Prasad, 2013;Xiong et al, 2017;Yang et al, 2019;Zhang et al, 2019). The second method is to quantitatively analyze the pore characteristics of different components by the direct SEM image observation (Wang et al, 2016b;Adeleye et al, 2017;Sun et al, 2018;Zhang et al, 2018). The third method uses a mathematical model to quantitatively calculate the contribution of different components to total pore structure parameters (Wang et al, 2014).…”

A novel upscaling procedure for characterising heterogeneous shale porosity from nanometer-to millimetre-scale in 3D

“…µm in Haynesville shale (Klaver et al, 2015), 200 µm in Toarcian shale (Houben et al, 2016) and 300 µm in Eagle Ford shale (Adeleye and Akanji, 2017). REV is slightly larger than REA in the same Haynesville-Bossier Shale Formation (Klaver et al, 2015).…”

Contrast‐enhanced nano‐CT reveals soft dental tissues and cellular layers

“…It can be defined as the distance between the two parallel planes restricting the object perpendicular to that direction (Febbi et al 2015). Furthermore, skewness is a measure of lack of symmetry, and kurtosis evaluates the degree of flatness of tubuli (Adeleye & Akanji 2018). All 3D illustrations were performed in CTVox (version 3.0, Bruker micro-CT) or Avizo ® (Thermo Fisher Scientific) using computer-generated colours for specific ranges of attenuation in the sample.…”