Effects of Echo Time on NMR Apparent Porosity and Correction Methods

Abstract

In order to study the effect of echo time (TE) on nuclear magnetic resonance (NMR) porosity in tight oil (gas) and shale reservoir, multi-TE NMR experiments and NMR numerical simulations were performed on CuSO4 solutions with specific transversal relaxation time (T2). The results showed that the normalization NMR porosity of different T2 relaxation components remained 100% in the low TE region, and rapidly decreased with increasing TE. When TE was greater than certain value, the normalization NMR porosity dropped to zero. However, the TE value at which the normalization NMR porosity began to decrease and the TE value at which the normalization NMR porosity dropped to zero were different for different NMR relaxation component. Moreover, the whole NMR measurement was divided into lossless zone, fast decay zone, invalid parameter zone and instrument blind zone, based on the relationships between the normalization NMR porosity of different relaxation component and TE. For each specific relaxation component, a logarithmic relationship was demonstrated between the loss of relaxation component and TE in the fast decay zone. A method for NMR porosity correction was given.

Keywords

• nuclear magnetic resonance (nmr)
• echo time
• nmr porosity
• component loss
• numerical simulation