Application Of XRay Imaging Techniques To Oil Sands Experiments

Abstract

Abstract Well controlled laboratory experiments are the key to understanding bitumen recovery from oil sands deposits and measurement of basic parameters required to predict field performance. The inability to see what is happening inside test cores is a serious limitation to experimental interpretation. This paper describes the application of three unique X-ray based techniques developed at the Alberta Research Council for Visualizing process behaviour and for measuring fluid saturations. This capability has evolved from one-dimensional single beam attenuation, to two-dimensional xeroradiography, and finally to full three-dimensional computed tomography. The first system uses a single beam approach to directly measure bitumen and water saturations for relative permeability determinations on oils and cores at in situ steam conditions. The second system, X-ray xeroradiography, is a qualitative technique developed to visualize encased field cores and coreflood experiments. The xeroradiography concept has a number of subtle features which lead to high contrast easily read two-dimensional images of internal core structure and fluid distributions. The third system, X-ray computed tomography, provides a fun three-dimensional imaging capability. The image data are used to provide high resolution quantitative analysis of core structure and fluid saturations. The three complementary techniques provide a unique capability for the study of oil recovery processes. This paper discusses some results of petrophysical studies and the measurement of saturations during coreflood experiments. Introduction In the past, a number of methods have been reported for non-instrusive measurement of fluid saturations in coreflood experiments. These include the use of microwaves(l), X-ray and x-ray attenuation (2,3,4,5), neutron attenuation(6), X-ray computed tomography(7,8), and nuclear magnetic resonance(9), Each of the techniques has unique features which provide information on core properties. Attempts to apply these technologies to oil sand corefloods provides an added challenge. The heavy oil or bitumen component is highly viscous and immobile at room and reservoir temperatures. This means that most displacement type experiments are usually conducted at the elevated temperatures typical of those encountered in thermal recovery processes. An added complication is that the porous sand medium is unconsolidated which requires the use of special core sleeving and pressure containment equipment for flooding experiments. The X-ray attenuation technique had been successfully applied to conventional corefloods(2,3) to provide on-line saturation data. The basic principle of this method is that the reduction in beam intensity as it passes through a fluid filled core is a function of the atomic composition and density of the components. Because of this dependence, transmission measurements arc reduced to core structure and saturations from a knowledge of the component attenuation coefficients. This method was incorporated into a high temperature and pressure coreflood apparatus to measure chordal average saturations and saturation profiles during bitumen/water displacement experiments. Reproducibility of coreflood data is often controlled by the porous medium, in this case, an unconsolidated sand. To help assess the basic core structure a second attenuation method xeroradiography, was implemented into a core-pack screening facility. The physical set-up is similar to conventional radiography, however, images are created on an electrostatically charged semiconductor plate rather than photographic film.