Predicting the impact of hydrocarbon saturation on T2 distribution curve of NMR logs – A case study

Abstract

The Nuclear Magnetic Resonance (NMR) is a valuable technique that provides estimates of various rock and fluid properties, including porosity, permeability, and pore size distribution. The decay or relaxation time of NMR signals is directly related to the pore size, but altering fluid in the pore spaces would also change the T 2 distribution curve. This change is due to the different relaxation time of hydrocarbon and water. This study focuses on predicting NMR T 2 distribution curves at different water saturations using a single T 2 saturation at any given water saturation. To do so, NMR measurements were performed on 9 plugs each at different saturations. Two general equations were derived. The first equation is related to the water response, while the second equation is related to the oil response. These two equations were calibrated and verified using core data. The coefficient of determination (R 2 ) for the first equation is equal to 0.592, while it is equal to 0.975 for the second equation. T 2 distribution curves depend on the amount and the distribution of the fluids within the pore structure. The findings of this study can help to increase the accuracy of the petrophysical properties derived by NMR logging. • A new model is proposed to predict NMR's T2 distribution curve in the oil bearing rocks. • NMR measurements were investigated in 9 plugs individually in different saturations in an oil field. • Two general equations were derived. To validate the equations, five T2 distribution curves which are equivalent to the T2 distribution curve of 100% water saturated rock were constructed by using 5 experimental T2 distributions.