https://cyberleninka.org/article/n/22310.pdf

Pore-scale imaging and modelling

/pdf/high-resolution-x-ray-computed-tomography-in-geosciences-a-3sj7249knj.pdf

High-resolution X-ray computed tomography in geosciences: A review of the current technology and applications

http://research.engr.oregonstate.edu/immiscibles/sites/research.engr.oregonstate.edu.immiscibles/files/Papers/Wildenschild_Sheppard_AWR_2012.pdf

X-ray imaging and analysis techniques for quantifying pore-scale structure and processes in subsurface porous medium systems

In the last 3 years there has been a huge increase in the use of pore-scale modeling to study multiphase flow and transport in porous media. Starting from single pore models of fluid arrangements, computations of relative permeability, interfacial area, dissolution rate and many other physical properties have been made. Combined with a realistic description of the pore space, predictive modeling of a variety of processes, including waterflood relative permeability and mass transfer coefficients, is now possible. This review highlights some of the major advances, with an emphasis on models of wettability and three-phase flow.

Flow in porous media — pore-network models and multiphase flow

Detailed physics, predictive capabilities and macroscopic consequences for pore-network models of multiphase flow.

We test the accuracy of pore network models generated from microtomographic images by comparing computations of permeability and wetting fluid continuity based on the images and network models extracted from the images. The comparisons are made for three rock-types including two clastic rocks (consolidated and unconsolidated) and one outcrop carbonate. We describe the network extraction procedure and note the nonunique aspects of the resultant networks and the effect which this has on predictions of permeability. Permeabilities are found to be in very good agreement for large image volumes (>10,000 pores). At a local scale we compare the flow rates within individual pores for the image based computations with those for the network. Whilst there is considerable scatter in the data, the overall trends are similar. We also question the merits of the usual network model assumptions that every pore and throat in the network has a uniform cross-sectional shape, determined from an equivalent shape factor, and that corner wetting fluid remain continuous throughout the network. An image based investigation of the connectivity of the crevice wetting phase shows that corner wetting phase becomes increasingly disconnected as the wetting phase saturation is reduced.

Pore-level validation of representative pore networks obtained from micro-ct images

This paper presents results of a 3D pore scale study of the resistivity properties in twelve model and reservoir core samples. Samples include sintered bead packs, homogeneous consolidated sandstones, thinly bedded sands, sucrosic dolomites, dual porosity samples and heterogeneous carbonate core material. Predictions of Archie’s cementation exponent m and saturation exponent n (under well defined wettability conditions) are in good agreement with experiment where available. We note a consistent increase in m with decreasing porosity in sandstones. The value of m in carbonates may be empirically related to the fraction of disconnected macroporosity. Under water wet conditions the simple clastic and carbonate samples exhibit Archie-type behaviour. The laminated sand exhibit strong anisotropy and the complex carbonate systems exhibit values of n that vary strongly with water saturation. Large values of n>4 are observed under idealized oil wet conditions. Pore and fluid phase connectivity is examined for the image data and used to explain trends observed in the data.

/pdf/pore-scale-analysis-of-electrical-resistivity-in-complex-dly5s52twy.pdf

Pore scale analysis of electrical resistivity in complex core material

Descriptions of rock fabric and texture are of great value to geologists and petrophysicists as they can be used in facies analysis and in the interpretation of the environment of deposition. Grain shape and size information is used to correlate to petrophysical properties. They are also of importance to the production technologist for completion design and sand strength/failure prediction. Textural descriptions are traditionally obtained via petrographic and petrological analysis including thin section analysis, particle sieving techniques and laser diffraction studies. All methods have limitations in quantitatively describing the full 3D rock fabric and assumptions and interpretations in the processing of data can skew or distort predictions of textural data. We have previously demonstrated the ability to image, visualize and characterise sedimentary rock in three dimensions (3D) at the pore/grain scale via X-ray computed microtomography [1, 2]. We now demonstrate the ability to directly measure rock fabric and texture from 3D digital images of core fragments. The mathematical procedure to extract individual particles from a full core image is described and its accuracy demonstrated. A single core fragment image can yield more than 8,000 individual grains. We describe methods for mathematically characterizing the individual grains including grain size (max/min and mode, skewness, sorting, kurtosis) and shape (sphericity, roundness). These are measured in parallel with textural information (sorting, grain contacts, matrix/grain support). A comparison of grain size analysis from digital image data to laser diffraction studies on sister core material is shown; good agreement between estimates of grain size is obtained. Comprehensive grain shape data obtained over thousands of grains shows significant variability within samples and systematic shape changes with grain size. Measures of grain contacts and grain overlap area show that many grains are loose within the pack and larger grains can have coordination numbers greater than 20. Anisotropy in grain orientation is also directly measured. The rock fabric and texture derived from digital 3D images is more comprehensive, systematic and quantitative than current analysis techniques. This analysis, coupled with studies of 3D pore structure and the ability to directly measure petrophysical properties from 3D images, will enable one to embark on a systematic study of the effect of grain size, shape and cementation on transport and elastic properties of core material.

Rock fabric and texture from Digital Core Analysis

Digital Core Laboratory: Reservoir Core Analysis From 3D Images

A facility for digital imaging, visualizing, and calculation of reservoir rock properties in three dimensions is described. The facility includes a high-resolution X-ray microcomputed tomography (CT) system. The study demonstrates the potential to predict petrophysical properties from core material not suited for laboratory testing (e.g., drill cuttings, sidewall care, or damaged core) and the feasibility of combining digitized images with numerical calculations to predict properties and derive correlations for individual-reservoir rock lithologies.

Wolf Val Pinczewski

Papers

Pore-level validation of representative pore networks obtained from micro-ct images

Pore scale analysis of electrical resistivity in complex core material

Rock fabric and texture from Digital Core Analysis

Digital Core Laboratory: Reservoir Core Analysis From 3D Images

Digital core laboratory: Reservoir-core properties derived from 3D images