Study On Mechanism Of Two-phase Flow In Porous Media Using Micro Focused X-ray CT
Authors: Mikami Kazuaki , Mukunoki Toshifumi 
Published: March 2015

A technology of X-ray Computed Tomography (CT) has become one of the popular techniques in the medical and engineering fields as a non-destructive testing method. In general, there are three kinds of X-ray CT scanners for medical, industrial and micro focused applications. In particular, micro focused X-ray CT (MXCT) scanners with high energy x-ray beam attaining high resolution have been drastically developed in a decade. Meanwhile, the study with respect to multi-phase flow in porous media desires to get more quantitative parameters of the particle shape and pore structure to clarify the mechanism, such as residual oil trapping. Nowadays, techniques of image processing and analyzing are very developed worldwide so that it has been available to evaluate pore structure and the fluid behavior without any destruction. The objective of this study is to understand residual mechanism of oil in sandy soil during water flooding. In this paper, a newly developed apparatus of flow injection for MXCT scanner and image analyzing technique were introduced and then, the pore scale and its distribution in the specimen were evaluated as the achievement of the first objective. Additionally, the cluster analysis was applied to each trapped oil blobs extracted from MXCT images. This image processing technique allowed quantitative evaluation to pore structure of specimen and trapped oil blobs.

Introduction

Understanding multi-phase flow in porous media is very important in many natural and engineered processes; contaminant remediation of ground water, oil recovery processes, and geologic sequestration of CO2. Residual saturation which is a saturation of a liquid becoming immobile is a key factor affecting these processes on a long-term source of groundwater contamination, an efficiency of oil recovery and CO2 trapping. However, multi-phase flow can vary depending on the local pore structure, interactions between the fluids and rock-fluid interactions. Thus, quantitative parameters regarding particle shape and pore structure are often desired. Characteristics of the pore structure of rocks, such as pore size, shape, spatial distribution, and connectivity, are therefore important, and should be evaluated in three dimensions to understand the mechanism of residual oil trapping. Recent technologies such as X-ray computed tomography (CT) scanners have made possible nondestructive evaluation of pore diameter and distribution in the study of fluid behavior in porous media (Wildenschild et al., 2002; Altman, 2005; Wildenschild et al., 2005; Al-Kharusi & Blunt, 2007; Mukunoki et al., 2010). New techniques for image processing and analysis of X-ray CT images are thus now required (Mukunoki et al., 2011).

The objective of this study is to understand residual mechanism of oil in sandy soil during water flooding. In this paper, a newly developed apparatus of flow injection for MXCT scanner and image analyzing technique were introduced and then, the pore size and its distribution in the specimen were evaluated as the achievement of the first objective. Additionally, the cluster analysis was applied to each trapped oil blobs extracted from MXCT images. This image processing technique allowed quantitative evaluation to pore structure of specimen and trapped oil blobs. Specifications of the micro-focused X-ray CT scanner used in this study are in Mukunoki et al., (2011).