Oil And Gas Nmr Properties: The Light And Heavy Ends

Relaxation times of intermediate viscosity dead oils show a linear correlation with viscosity/temperature on a log-log plot. In contrast, dissolved methane at the low end and heavy crude oils at the other extreme fail to follow this correlation. It is well known that the presence of these components in an oil complicates analysis and interpretation. At the light end, ethane and propane are also common components of natural gas associated with oils at reservoir conditions. In spite of this fact, the Nuclear Magnetic Resonance (NMR) relaxation times of these materials have not been published at conditions typical of petroleum reservoirs. Their contributions to the relaxation of live oils are not known. In this work, the proton nuclear spin-lattice relaxation times and self-diffusion coefficients of ethane and propane were measured at typical reservoir conditions. The proton relaxation times were calculated and compared with the experimental data for ethane. The contributions of both spin rotation and dipole-dipole mechanisms were investigated. A mixing rule was developed to estimate T1 of gas mixtures. Finally, we compare the estimated results by the mixing rule with experimental results. At the other extreme, heavy crude oils also depart from the viscosity correlation. Consequently, 7"1, and T2 relaxation times of 20 heavy crude oils were measured with three different frequency NMR spectrometers. Relaxation time distributions of a light crude oil and a heavy crude oil are presented, as a function of the Larmor frequency. The effect of the echo spacing on T2 distributions of heavy oils is discussed. Then the dependence of the ratio of the logarithmic mean TI/T2 on oil viscosity, asphaltene content and the I＿armor frequency is investigated.