Discrimination of Crude Oil and Water in Sand and in Bore Cores With NMR Imaging

Abstract

Summary Nuclear magnetic resonance (NMR) imaging techniques were used to study the mobile proton content in prepared samples containing mixtures of crude oil, water, and sand. The measured proportions of viscous crude oil agree well with the actual values. proportions of viscous crude oil agree well with the actual values. Discrimination of light crude oil and water was demonstrated by proton, chemical shift differences. A bore core sample also was proton, chemical shift differences. A bore core sample also was examined and gave clear images from its oil content. Introduction Research on the displacement of crude oil by other fluids-e.g., water, natural gas, nitrogen, carbon dioxide, or aqueous solutions-seeks to determine the efficiency of oil recovery and the stability of such a process under various conditions. To study the relative importance of the factors that influence oil displacement research, nonintrusive X-ray and neutron radiographic techniques have been developed to measure the flood saturations and flow patterns in high-pressure coreflooding experiments. With these patterns in high-pressure coreflooding experiments. With these measurements, it is possible to distinguish two or more phases within samples contained in steel or alloy pressure vessels. phases within samples contained in steel or alloy pressure vessels. X-ray computed tomography (CT) was another method developed for medical and industrials applications and can be used to obtain information on the distribution and flow of fluids within core samples. NMR measures fluid saturations and relative permeabilities in drill core material, but the new technique of NMR imaging now offers a promising means to determine the distribution, flow, and mobility behavior of proton-containing liquids in solids. To date, the major application of NMR imaging is in medicine, where it detects differing water concentrations among the various tissues and organs of the human body. The information obtained in a noninvasive manner yields detailed two- or three-dimensional images of the interior structure of animals and humans. In addition to the medical and biological uses of NMR imaging, a number of solid- and liquid-state applications in the study of materials could be used in the petroleum industry. Because NMR imaging measures more than proton density, it is inherently more informative than radiographic techniques. It is also much less hazardous. Special features of many NMR imaging techniques include the ability to measure the flow of liquids and to distinguish between two different static liquids using the differences in intrinsic NMR properties, such as the spin-lattice and the spin-spin relaxation times, t and t, and chemical shifts. With these properties, NMR imaging has the potential to provide detailed information properties, NMR imaging has the potential to provide detailed information about the chemical nature of different fluids. This type of information would be difficult (if not impossible) to obtain by other methods. The extent to which the potential for core analysis is realized undoubtedly will depend on instrumental developments in the NMR imaging technique. In this paper we present a preliminary evaluation of the applicability of NMR imaging to measure oil and water in core material. We examined fabricated samples containing known concentrations of crude-oil/water mixtures dispersed in sand where both the effect of different crude oil types and diffusion of water were monitored. An actual core sample also was examined. Experimental Procedure Samples. Three 1.97-in. [50-mm] -diameter glass tubes were packed in different sections (Sections A through E) with different concentrations of crude oil, water, and sand (see Fig. 1). Sample 1 was packed with a highly viscous aromatic crude oil (Tia Juana Persado), and the different compartments were isolated from each Persado), and the different compartments were isolated from each other by rubber membranes. Sample 2 was constructed similarly but without rubber membranes so that diffusion of fluids could occur. In addition, this sample contained a globule of oil in Section E. The imaging measurements were made about 2 months after the sample had been constructed. Sample 3 used a much less aromatic and more mobile crude oil (North Sea Brent field) and incorporated rubber membranes. It was imaged about 7 days after construction. NMR Imaging Measurements. All NMR measurements were made with proton resonances at 30 x 106 cycles/sec [30 MHz]. proton resonances at 30 x 106 cycles/sec [30 MHz]. SPEFE P. 31