NMR response of liquids and of natural gas mixtures
Hirasaki, George J.
Doctor of Philosophy
This research relates T 1 and T 2 to thermodynamic and transport properties, such as composition and possibly density and viscosity, for types of reservoir fluids that have not previously been systematically studied using nuclear magnetic resonance (NMR). NMR measurements, which provide quantitative values including relaxation times T 1 and T 2 , assist in detecting and characterizing formation oils and gases. This work involves NMR laboratory experiments at a 1 H frequency of 2 MHz. Thermodynamic and transport properties are established by sample preparation or are obtained by measurement or are based on available data. Then, the connection between these properties and NMR data is developed or assessed. These relationships are the basis of NMR correlations. Previous correlations have been developed for linear alkanes, for oil mixtures containing methane, and individually for methane and ethane. A theoretical model exists for natural gas mixtures. The current work addresses three situations that existing correlations do not treat. First, results appear for NMR estimation of crude oil contamination by base oils. The presence of base oils interferes with NMR assessments of crude oils. Relating T 2 measurements to the level of contamination provides the answer, shown for three separate crude oils mixtures with a base oil contaminant. This work develops two novel evaluative parameters, namely selective contamination index (SCI) and distribution parameter index (DPI), to interpret the effect of contamination of crude oil with base oils. The SCI and DPI surpass standard methods in the precise determination of the degree of contamination. The second topic is assessing T 1 and T 2 for cyclic molecules and base oils. Though monocyclic aromatic and aliphatic molecules deviate from alkane correlations, it is found that bicyclic compounds and base oils do not. Another situation this work addresses is the determination of T 1 and T 2 for gaseous mixtures of methane and other natural gas components. The measurements illustrate the effect of density and composition on NMR assessments. Methane and ethane measurements are presented, as are measurements and interpretation for gas mixtures. The latter measurements show good agreement with NMR gas mixing rules.