Quantifying Water Saturation in Steel Pipes using X-rays

Abstract

An experimental apparatus has been built to measure the relative permeabilities of water and steam in a two phase flow through porous rock for a range of flow configurations and conditions. In the experiment, the pressure gradient will be measured and consequently the relative permeabilities are determined as a function of flow rate of the two phases. In addition we would like to determine the relative permeabilities as a function of the volume fraction of the liquid (water saturation) in the two phase flow. It is therefore important to make direct measurements of the water saturation at various locations in the experimental apparatus. In this paper, X-ray imaging equipment (moveable C-beam) was used to quantify the liquid fraction in steel pipes filled with different materials. The experiments were done using steel pipes of different diameter and wall thickness. Our preliminary results showed that useful X-ray images could not be obtained with wall thickness greater than 8 mm with the X-ray equipment at hand, most likely because of limited energy of the beam (max of 106 keV). X-ray penetration was sufficient when we limited pipe diameter to 100 mm and thickness less than 8 mm. This method was used on a pipe with diameter 76 mm and wall thickness 4.5 mm and filled with angular quartz fragments in effort to simulate a geothermal reservoir. The pipe was subsequently filled gradually with water while taking X-ray images every step of the way. Using image software to evaluate the images from our experiments we observed that as we added water into the pipe the grayscale of the image changed gradually. To obtain an absolute scale for the grayscale of the images we used a step wedge made of steel. This experiment shows that we can use X-ray imaging, along with absorption reference for comparison (step edge) to quantify water saturation in steel pipes.