Proton T1 and T2 relaxivities for CH2 and CH3 peaks in crude oil measured by 400 MHz NMR

Petroleum fluid has been extensively studied at low magnetic fields by Nuclear Magnetic Resonance (NMR) Spectroscopy, but high field NMR studies are rarely found in this area. The aim of this study is to determine the proton spin-lattice relaxation rate (1/T1), T1 relaxivity (R1), proton spin-spin relaxation rate (1/T2) and T2 relaxivity (R2) of paraffinic CH2 and gamma CH3 peaks. For this purpose, crude oil samples were taken from 3 separate wells in the Batman region. Using these samples, 3 different sets were prepared from a mixture of deuterated chloroform (CDCl3) and crude oil. The total volume of each prepared mixture was 1 mL. The crude oil content in each set was changed from 0.05 mL to 0.20 mL in 0.05 mL steps.. Special care has been taken to ensure the best shimming of the NMR spectrometer operating at 400 MHz. T1 measurements were performed using an inversion recovery (IR) pulse sequence. 1/T2 values were determined from the half-height line widths of CH2 and CH3 peaks. 1/T1 and 1/T2 rates and all relaxivities were found to vary from well to well. This change is due to the fluid composition of the wells. The 1/T2 rates and R2 relaxivities were found to be considerably greater than the 1/T1 rates and R1 relaxivities. R2 relaxivities for CH3 were also 2-5 times greater than for CH2.The higher 1/T2 and R2 relaxivities compared with 1/T1 and R1 were attributed to the additional CDCl3-mediated relaxation mechanisms. In conclusion, available data show that high 1/T2 rates and R2 relaxivities measured in the high field NMR laboratory can be applied to separate crude oil from other fluids in the oil field