The study of multi-phase flow in porous media using dual-gamma ray
Date Issued
2009
Date
2009
Author(s)
Wang, Yao-Lin
Abstract
This study follows Lee (2006) using the Gamma-ray attenuation theory to establish non-destructive measuring equipment. To measure nonaqueous-phase liquid (NAPL) and water contents simultaneously, a collinear dual-energy γ-radiation system is employed. The radiation sources are 241Am and 137Cs. A one-dimensional (1-D) multiphase flow experiment is conducted to investigate the distribution of dense-NAPL (DNAPL) in the subsurface at steady state. Both holder and detector possessed lead shielding with a 2.8-mm-diameter. Before the experiment we find the variation of measuring counts is large when measuring the soil sample. That is the measuring volume does not reach representative elementary volume (REV). So the porosity ( ) has uncertainty. From the Gamma-ray attenuation theory, the uncertainty of measuring saturation comes from counts, porosity and porosity combining saturation. his study uses Gauss probability density function to fit the measurements peak-value. This method can decrease the variation of counts and saturation. The largely variation is porosity. So at attenuation coefficient test, the method only measures the fluid and not includes sand which can get less prediction interval of saturation. When the measuring volume is ten times of one single measuring volume, it may be regarded as REV. Analysis attenuation of dual-gamma source to each material that 241Am can differentiate each material easily and 137Cs can’t distinguish the material.his study uses Quartz sand as porous medium and HFE-7100 as DNAPL. We can get water-air soil experiment data of capillary pressure (Pc) and saturation (S) during primary drainage. Then the measured air entry-pressure can be used to calculate the DNAPL entry-pressure. From water primary drainage (DNAPL imbibition) process within water-DNAPL two-phase fluids, we can get DNAPL entry-pressure. The experimental results are close to the theoretical values. Then we can use it to design 2-D experiment in the future. Through gamma ray measurement and visualization, we can know distribution of the DNAPL accurately. At water-DNAPL-air three-phase fluids, the initial condition is DNAPL-saturated and water-residual. We observe water and DNAPL drainage (air imbibition) at the same time then get Pc-Scurve. The saturation of DNAPL near ground water table is approximately 25%. And the DNAPL residual is few and unable to be distinguished.o sum up, we suggest that modulating the thickness of sand box and the diameter of gamma beam to maintain the quantity of counts. We can reduce the variation of heterogeneity and increase precision by measuring at REV scale.
Subjects
non-destructive measuring
dual-gamma ray
REV
Pc-S curve
Type
thesis
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