Visualization of Laboratory Corefloods With the Aid of Computerized Tomography of X-Rays

Abstract

Summary. This paper presents the use of X-ray tomography to inspect a series of laboratory core-displacement tests. Saturation profiles in thin longitudinal planes of view (slices) in the core are followed as a function of time. Immiscible and miscible displacements in single core plugs and butted composite plugs are presented. Effects of heterogeneity of the core, dispersion of flood fronts, and end effects are observed and discussed. The technique has a large potential to improve the understanding of fluid displacement processes in laboratory core experiments. Introduction Data from laboratory displacement tests on reservoir rock samples are widely used as input parameters in reservoir simulators. Questions on the validity of these data are frequently asked concerning sample heterogeneity, dimensions, end effects, analysis procedures, and conditions. One way to study these effects would be to follow the movement of the fluids inside the reservoir rock sample. Several methods are used to visualize or to quantify saturations during laboratory displacement experiments. Some of these are based on radioactive tracers or an external source, nuclear magnetic resonance, microwaves, and electrical properties. All these methods give only a one-dimensional presentation of saturation. Computerized tomography of X-rays for medical purposes was introduced in the 1970's. Because this tool gives a two-dimensional (2D) image of the interior of an object, it should also provide information on reservoir rock. In our evaluation of the technique and commercial scanners, we performed several displacement tests using different displacement methods. Some of these tests are presented in this paper. However, no systematic study was undertaken to analyze the different parameters' influence on displacement behavior. Principle of Computerized Tomography of X-Rays Radiation of high energy can penetrate material of moderate density, such as reservoir rock. The problem is to reconstruct a detailed image contained in the attenuated high-energy rays transmitted. In 1917, Radon showed mathematically how to unscramble the information in the attenuated energy rays. A geometric interpretation of Radon's theorem emerged in 1972 with a technique called computerized tomography (CT). The device is called a CT scanner. Any object of moderate density is placed between an X-ray source and an array of collimated detectors. The source and detectors are mounted on a "yoke" that rotates. Power is pulsed to the X-ray tube, creating a fan of beams that traverses a thin slice (I to 8 mm [0.04 to 0.3 in.]) of the object (Fig. 1). Between each power pulse the yoke moves, and the next X-ray fan beam traverses the same slice from a slightly different angle. As the yoke is rotated 6.3 rad [360 degrees], as many as 700,000 different X-ray projections are available for mathematical processing. A presentation of the mathematical treatment is found in Ref. 10. The mathematical processing, performed by a computer, gives a synthesized image. The basic synthetic unit is the volume element. The CT slice is composed of many volume elements, each with its own characteristic attenuation, which are displayed as a 2D image matrix of picture elements (pixels) (Fig. 2). Because X-ray attenuations are related to density, the CT image gives the density distribution within every point of the object scanned. Because it is impractical to deal with the X-ray attenuation coefficient, A, in CT scanning, a new relative scale was defined as (1) where mutc = calculated X-ray attenuation coefficientandmuH2O = X-ray attenuation coefficient for water. SPERE P. 148^

A review of non-invasive imaging methods and applications in contaminant hydrogeology research

“…In particular, it has seen significant use in characterizing porous-media structure and fluid-displacement processes for the purpose of improving our understanding of oil recovery (e.g., Wang et al, 1984; Hove et al, 1987; Vinegar and Wellington, 1987; Wellington and Vinegar, 1987; Withjack, 1988; Hicks et al, 1992). Standard X-ray CT has also been used in the environmental field, for example, to measure fluid saturations during bench-scale experiments investigating the migration of organic liquid (e.g., Fagerlund et al, 2007; Goldstein et al, 2007).…”

Waterflood in Vuggy Layer of a Middle East Reservoir - Displacement Physics Understood

“…Due to the complex sub-core scale heterogeneity of vuggy lithotypes, the process was modified to use whole core instead of the standard 3.8 cm diameter core plug and to use X-ray CT ( Figure 1) [5,6,7] instead of gamma ray adsorption monitoring (GASM) to measure the in-situ saturations.…”

Efectos de productos dopantes en fluidos para pruebas de desplazamiento usando tomografia computarizada

“…Sin embargo, la disponibilidad de técnicas de imágenes para la visualización tri-dimensional detallada de la muestra y visualización del movimiento de fluidos en el medio poroso durante el desplazamiento, ha sido reportada por (Wang, et al, 1984), (Hove, et al, 1987), (Vinegar & Wellington, 1986), (Hunt & Engler, 1987), (Withjack, 1988), (Withjack, 2003). Estos autores presentan los resultados de estudios hechos usando tomografía computarizada (CT) para observar el proceso de desplazamiento in-situ.…”