T1–D–T2 correlation of porous media with compressed sensing at low-field NMR

Publication date: Available online 2 October 2018

Source: Magnetic Resonance Imaging

Author(s): Yan Zhang, Lizhi Xiao, Xin Li, Guangzhi Liao

Abstract

3D Laplace NMR can distinguish different components of confined fluid in sedimentary rocks, which is important to oil industry. However, the measurement time for such experiments is very long, which hinders the application in some cases such as NMR well logging. In this research, we accelerated T₁–D–T₂ experiment with compressed sensing (CS) method at low-field NMR. Simulation was first performed to examine the CS reconstruction method. The experiments were subsequently implemented on a 2 MHz spectrometer (Oxford instrument), which has a similar magnetic field strength to well logging tool. The T₁, D and T₂ information are obtained by the inversion recovery, pulsed field gradients and Carr–Purcell–Meiboom–Gill (CPMG) method, respectively. The subsampling is applied in T₁ and D dimensions with pseudo-random sampling. The measurement time reduced from 3 h to 0.6 h with CS method and a relative error of around 5% is achieved for data with signal-to-noise ratio of 28. The water and oil peaks are clearly distinguished in the correlation maps from subsampled data. The samples with different oil-water ratio and glass bead volume fraction were measured to examine the sensitivity of this method. In addition, diffusion and relaxation properties of the correlation maps are discussed.

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