DEVELOPMENT OF NUCLEAR MAGNETIC RESONANCE IMAGING/SPECTROSCOPY FOR IMPROVED PETROLEUM RECOVERY

The overall objectives of this program are to develop and apply Nuclear Magnetic Resonance Imaging (NMRI) and CT X-Ray Scanning methods for determining rock, fluid, and petrophysical properties and for fundamental studies of multiphase flow behavior in porous media. Specific objectives are divided into four subtasks: (1) Subtask I: The development of NMRI and CT scanning for the determination of rock fluid and petrophysical properties The initial stage of this research involved measurement of porosity and two-phase saturations of reservoir rocks on a global and on a local basis. From the distribution of these properties within core samples, a statistical measure of the heterogeneity of the core, called the correlation length, was developed. Secondly, we designed and built a core holder suitable for NMR experiments which can withstand pressures up to 2000 psi. Thirdly, we used NMRI and conventional techniques to evaluate the effectiveness of a biopolymer as a mobility control agent in enhanced oil recovery processes. (2) Subtask 2: Development of NMRI and CT scanning for characterizing conventional multiphase displacement processes Experimental methods and computational procedures were developed for acquiring and analyzing fluid phase distributions during two-phase immiscible fluid displacements in order to estimate porosity and saturation distributions with great accuracy. Other computational procedures were developed for estimating two- and three-phase relative permeability functions from displacement data that includes those measures of the saturation distribution. New approaches for characterization of fluid distributions and pore structures using NMR relaxation and restricted diffusion measurements were investigated. In particular, apparent diffusivities were introduced for characterizing pore sizes in different model porous media. Methods for analyzing diffusivity distributions, arising from diffusional processes in different compartments of fluids, were developed. In addition, saturation-dependent relaxation measurements were carried out to study fluid distributions at different saturation levels. Computational procedures for obtaining those distributions were developed. (3) Subtask 3: Development of NMR and CT scanning for characterizing dispersed phase processes In subtask 3, we have successfully developed the technique of using NMR relaxation methods to characterize wettability of porous media. The method has been thoroughly investigated in model porous systems with different surface wettability properties. Through these extensive and systematic studies, we have clarified some confusion on this technique caused by previous researches. We have also tested this technique on rock samples. We demonstrated that the NMR relaxation method can become a fast and convenient tool for characterizing wettability of porous media. To enhance the oil recovery in fractured, low permeability reservoirs, we studied a surfactant based imbibition/solution gas drive process. NMR imaging is a powerful tool for studying such processes. Very encouraging results were obtained which revealed the potential use of this new process for enhanced oil recovery. We also used NMR restricted diffusion and X-ray CT scanning methods to study the behavior of dispersed phases in porous media. The data provided by these studies are of great importance in developing improved theories of dispersed phase flow in porous media. (4) Subtask 4: Miscible displacement studies. Miscible flooding is a form of enhanced oil recovery whereby injected solvents are miscible, or develop miscibility, with the in-place oil. Miscible flooding is complicated by the formation of viscous fingers which lower volumetric sweep efficiency and ultimately lower oil recovery. The objectives of Subtask 4 are: (1) to develop the CT scanner as a general tool to study flow in porous media, with specific interest for studying miscible displacement and (2) to demonstrate the utility of the CT apparatus by studying the mechanics of viscous fingering. We have successfully developed the CT scanner by developing viable experimental procedures and equipment. These include:  (1) designing a core containment device, (2) designing a flow system, (3) developing viable CT scanner operating procedures, (4) developing data transfer procedures from the CT scanner to post-processors, and (5) developing post-processing software for image reconstruction.  Our experimental methods have been tested by successfully applying the CT scanner to study viscous fingering in laboratory core samples. The utility of the CT scanner is demonstrated by showing two-dimensional cross-sectional images of viscous fingers using state-of-the-art image processing software. This work contributes to our understanding of viscous fingering and will be helpful in future studies.

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