Development of Light Transmission Techniques for Quantification ofCO2 Trapping in Porous Media

Abstract: Light transmission can be used to measure the amounts of certain constituents within a system by analyzing the amount of light they have absorbed. The aim of this study was to improve methods for light transmission measurements in two phase systems. In this study, the main reason is to be able to use light transmission for measurements of CO2-trapping in natural sandstone. The latter is something that does not exist today. The study investigated the possibility to use selected liquids that both represent an analogue CO2-brine system and have similar refractive index as each other to simplify Beer-Lamberts law. The simplification suggested that a change in light intensity within a system was controlled solely by the length of a liquid that had replaced another liquid. Two methods were implemented to test this. A tank containing high transparency sand and glycerol was injected several times with dyed oil in order to test equations developed to calculate the length of oil that light had passed. The glycerol and oil were chosen due the ratio between them in density and viscosity. These are properties that make them ideal for modelling the trapping of supercritical CO2 in sandstone saturated with brine. The other method for testing was to measure a coefficient of light absorption for the oil, then applying that coefficient to an injection of a known volume of oil. The analysis results showed that a linear relationship exists between difference in light intensity and the volume of oil in a system. The developed equation for oil length, as a function of light absorption specific for that oil, is sufficient for calculating the volume of oil in the system. It could not be used for calculating exact values in each part of the tank. The placement of oil was crucial to the measured light intensity for a single point. Oil occuring further back in the tank gave lower values of light intensity than oil occuring in the front. The study show that with further investigation into the role of oil placement in the light path, a simpler method could be developed for some light transmission measurements. The method could be used in its current form for modelling CO2 in sandstone but should be further developed if exact values are important