Classification and quantification of pore shapes in sandstone reservoir rocks with 3-D X-ray micro-computed tomography

Mayka Schmitt,Matthias Halisch,Celso Peres Fernandes,Cornelia Müller

doi:10.5194/se-7-285-2016

Abstract

Abstract. Recent years have seen a growing interest in the characterization of the pore morphologies of reservoir rocks and how the spatial organization of pore traits affects the macro behavior of rock–fluid systems. With the availability of 3-D high-resolution imaging, such as x-ray micro-computed tomography (µ-CT), the detailed quantification of particle shapes has been facilitated by progress in computer science. Here, we show how the shapes of irregular rock particles (pores) can be classified and quantified based on binary 3-D images. The methodology requires the measurement of basic 3-D particle descriptors (length, width, and thickness) and a shape classification that involves the similarity of artificial objects, which is based on main pore network detachments and 3-D sample sizes. Two main pore components were identified from the analyzed volumes: pore networks and residual pore ganglia. A watershed algorithm was applied to preserve the pore morphology after separating the main pore networks, which is essential for the pore shape characterization. The results were validated for three sandstones (S1, S2, and S3) from distinct reservoirs, and most of the pore shapes were found to be plate- and cube-like, ranging from 39.49 to 50.94 % and from 58.80 to 45.18 % when the Feret caliper descriptor was investigated in a 10003 voxel volume. Furthermore, this study generalizes a practical way to correlate specific particle shapes, such as rods, blades, cuboids, plates, and cubes to characterize asymmetric particles of any material type with 3-D image analysis.

Highlights

Natural and artificial materials are often characterized by their pore/grain shape or size distributions as determined by distinct analytical instruments
To identify and characterize pore ganglia from a 3-D segmented pore volume, finding a lower cutoff limit for the ratio Vp/(Rv)3, i.e., a pore volume size in voxels (Nv), which allows us to distinguish pore ganglia to be suppressed from the real pore system, is necessary
Because the intention was to perform a comparative study for the classification and quantification of pore shapes among the three analyzed rocks, a common lower cutoff was www.solid-earth.net/7/285/2016/

Summary

Introduction

Natural and artificial materials are often characterized by their pore/grain shape or size distributions as determined by distinct analytical instruments. Several investigations have been conducted to classify pore types/shapes, and most of them are associated with 2-D quantification. A 3-D pore with irregular shapes cannot be appropriately characterized from 2-D image sections in pore-typing procedures, nor can the number of pores (Buller et al, 1990). Knowledge of pore morphologies is essential and they are one of the main parameters that control fluid flow underground. Petrophysical properties such as permeability, electrical conductivity and drainage capillary pressure are strongly influenced by throat sizes, which are constrictions of minimal cross-sectional area between pores (Buller et al, 1990). To the best of our knowledge, the systematic 3-D pore shape quantification of sedimentary rocks based on sample size, pore network detachment (i.e., separation into individual pores), and distinct geometrical descriptor measure-

Methods

Results

Conclusion