A novel low field nuclear magnetic resonance analyzer for porous media

Key words:  NMR analyzer  low field  porous media  Halbach magnet  measurement efficiency

Abstract:

A novel low field nuclear magnetic resonance (NMR) analyzer for porous media was presented. The analyzer permits analysis on water-saturated full cylindrical cores either in the laboratory or at the oil-well field with one-dimensional or two-dimensional measurements, and it can provide T₂ distribution, T₁ distribution and 2D T₁-T₂ maps. The rock test results show that porous media including rock can be measured accurately by one dimensional and two dimensional methods via the analyzer.The sensor consists of an improved Halbach magnet and exchangeable solenoid coils with slotted Faraday shielding. The low cost, linear power amplifier built in IRF510 and IRF640 produces power up to 250 W with gain of about 50 dB. The active de-coupler uses MOSFET controlled by digital circuit to protect the receiver channel. The gain of wideband preamplifier is 56 dB; the first stage utilizes a low noise wideband discrete RF transistor so that the noise introduced by the preamplifier is negligible. The digital signal processor (DSP) and field programmable gate array (FPGA) are employed to obtain the flexible logic control and powerful data processing, to generate all timing and control signal based on one-dimensional or two-dimensional pulse sequence and obtain the echo train data with digital phase sensitive detection (DPSD).