The (T_2,D) NMR losgins method for fluids characterization

When oil, gas, and water are present in rock simultaneously, their signals on T_2 distributions of nuclear magnetic resonance (NMR) usually overlap each other. Therefore it is difficult to differentiate them by one-dimensional NMR logging. In this work, the Carr-PurcellMeiboom-Gill (CPMG) pulse sequence echo train data with multiple echo spacing is used to realize the (T_2,D) two-dimensional NMR logging method. The performance of the (T_2,D) two-dimensional NMR method for identifying fluids in different kinds of reservoirs, signal-tonoise ratios, and magnetic field gradient are studied in detail through numerical simulation. The results show that the (T_2,D) method is capable of recognizing oil reservoirs of low and mediate viscosity. With increasing ratio of signal to noise (SNR) and gradients of the outside magnetic field, it can discriminate oil and water better. For gas reservoirs, this method has some requirement to the magnetic field gradients for their values. And with the increasing of SNR, the (T_2,D) method can distinguish gas and water to a better degree. When the SNR of data is less than 70, it probably does not work for gas reservoirs. The ( T_2,D) experiments on fluid saturated rock samples with paramagnetic impurities were performed using a MARAN NMR spectrometer at a proton resonance frequency of 2MHz. The effectiveness of the (T_2,D) method has been verified.