Huabing Liu

Rapid determination of fluid viscosity using low-field two-dimensional NMR

The rapid prediction of fluid viscosity, especially the fluid in heavy-oil petroleum reservoirs, is of great importance for oil exploration and transportation. We suggest a new method for rapid prediction of fluid viscosity using two-dimensional (2D) NMR relaxation time distributions. DEFIR, Driven-Equilibrium Fast-Inversion Recovery, a new pulse sequence for rapid measurement of 2D relaxation times, is proposed. The 2D relation between the ratio of transverse relaxation time to longitudinal relaxation time (T1/T2) and T1 distribution of fluid are obtained by means of DEFIR with only two one-dimensional measurements. The measurement speed of DEFIR pulse sequence over 2 times as fast as that of the traditional 2D method. Using Bloembergen theory, the relation between the distributions and fluid viscosity is found. Precise method for viscosity prediction is then established. Finally, we apply this method to a down-hole NMR fluid analysis system and realized on-site and on-line prediction of viscosity for formation fluids. The results demonstrated that the new method for viscosity prediction is efficient and accurate.

Heavy oil component characterization with multidimensional unilateral NMR

Heavy oil is a complicated mixture and a potential resource and has attracted much attention since the end of last century. It is important to characterize the composition of heavy oil to enhance its recovery efficiency. A designed unilateral Nuclear Magnetic Resonance (NMR) sensor with a Larmor frequency of 20 MHz and a well-defined constant gradient of 23.25 T/m was employed to acquire three-dimensional (3D) data for three heavy oil samples. The highly-constant gradient is advantageous for diffusion coefficient measurement of heavy oil. A fast data-implementation procedure including specially designed 3D pulse sequence and Inversion Laplace Transform (ILT) algorithm was adopted to process the data and extract 3D T1D-T2 probability function. It indicates that NMR relaxometry and diffusometry are useful to characterize the components of heavy oil samples. NMR results were compared with independent measurements of fractionation and gas chromatography analysis.

Novel detection system for NMR logging tool

We present a novel detection system for nuclear magnetic resonance (NMR) logging tool with direct connection of receiver to low inductance antenna. The detection system contains receiver and signal acquisition circuit with high signal-to-noise ratio (SNR). The direct balanced connection of receiver to antenna increases SNR of the NMR signal. The first stage of receiver has a balanced input built on ultra low noise wideband operational amplifiers LMH6626. The maximum receiver gain is 105 dB and its frequency bandwidth is from 600 kHz to 1 MHz. The signal acquisition circuit uses Digital Signal Processor (DSP) and Field Programmable Gate Array (FPGA) to obtain the flexible programmable ability and powerful data processing. Its resolution is 14 bit and maximum sampling frequency is 40 MHz. The acquisition algorithm uses digital phase sensitive detection to obtain the amplitude and phase information of NMR signal. Tests show that a range of common NMR experiments can be performed with our system. The CPMG echo train with high SNR is acquired successfully.

New magnet array design for downhole NMR azimuthal measurement

In low-field NMR, depth information and radial profile information of downhole formation can be easily acquired with the help of static gradient magnetic field produced by permanent magnets, called downhole NMR imaging. Based on the hypothesis that the formation is homogeneous, average signals detected by centralized or decentralized sensors can provide enough information for petrophysical parameters. In fact, the inhomogeneity of formation may have serious impact on description of the characteristics of formation and oil/gas location which is rarely studied in NMR well-logging. To improve this, we design and implement a new quadrupolar magnet array aimed at achieving azimuthal measurement in this paper. A new quadrupolar magnet array is consisted of four bread-shaped magnets combined with additional small hexangular magnets to produce enough strength and high homogeneity of static field along with circumferential direction at deeper DOI (depth of investigation). Azimuthal measurements are achieved by using coil array combined with quadrupolar magnet array.