Optimal Halbach Magnet Array Design for Portable NMR Targeting Multiphase Flow Metering Applications

In this paper, a Halbach array-based nuclear magnetic resonance device for multiphase flow measurement is suggested. The design approach used simultaneously a 3-D finite-element method (FEM)-based software combined with particle swarm optimization algorithm. The goal of the design is to generate a relatively intense and highly homogenous magnetic field inside the target sensing area using a compact and lightweight magnet array. Simulation results on a device consisting of 12 Halbach arrays, each consisting of 12 cuboid permanent magnet elements of size 20 mm × 20 mm × 46.5 mm size, indicate that a highly homogenous magnetic field distribution of 0.890 T maximal intensity and 606 ppm homogeneity could be achieved within a probe cross section of 40 mm diameter when the Halbach arrays are distant from each other by a distance of 4 mm. This is adequate for the desired application while it leads to a light and compact overall Halbach array of 21.6 kg weight and 600 mm length. Experimental validation which was done using newly constructed two Halbach arrays of cuboid and trapezoid magnet elements, respectively, indicates a good match with FEM simulations. Furthermore, sensitivity analyses were performed to identify significant design variables for further optimization.

I. Introduction

Multiphase flow meters (MPFMs) that provide real-time measurement of the volumetric flow of each of these phases are crucial for optimal reservoir management. The design of a reliable and accurate MPFM for oil-gas fields still remains a challenging task because of the opacity of the multiphase flow, in addition to the harshness of the surrounding environment. This led researchers to suggest various complementary sensing techniques such as capacitance [1]–[3], conductance [3], [4], and ultrasonic [1], [5] sensors for the computation of the multiphase flow fractions, while the total flow rate is measured using either differential pressure sensors (e.g., Venturi or orifice flow meters) or Coriolis flowmeter [4]. Overall, these multiple-sensing devices have demonstrated accurate measurement for specific ranges of phase compositions and flow rates. However, they require a prior knowledge of some fluid parameters such as the densities of all single phases composing the fluid. -ray flow meters, such as Schlumbergers’s PhaseWatcher Vx spectra [6], were also successfully deployed in several oil fields. They primarily combine a Venturi meter to measure the total volumetric flow rate and a dual-energy gamma ray device to measure the concentrations of individual phases. The meter was reported to exhibit an acceptable 5%–10% relative error.