Edmund J. Fordham

Production and wetting properties of fluorinated diamond-like carbon coatings

Abstract The control of hydrophobicity of diamond-like carbon (DLC) surfaces has been studied by the use of CF4 etching plasma and by the deposition of fluorinated DLC (a-C:F) using mixtures of CF4 with butane and acetylene. The results indicate that the degree of fluorination (F:C ratio), and the hydrophobicity of the surface depend critically on both the elemental composition of the gas feedstock and the deposition parameters. There is a correlation between high levels of fluorination and hydrophobicity, although at high F:C ratios, the mechanical stability of the fluorinated surface may be compromised. A possible mechanism for the production of hydrophobic fluorinated surfaces is proposed.

Low-Field Permanent Magnets for Industrial Process and Quality Control

In this review we focus on the technology associated with low-field NMR. We present the current state-of-the-art in low-field NMR hardware and experiments, considering general magnet designs, rf performance, data processing and interpretation. We provide guidance on obtaining the optimum results from these instruments, along with an introduction for those new to low-field NMR. The applications of lowfield NMR are now many and diverse. Furthermore, niche applications have spawned unique magnet designs to accommodate the extremes of operating environment or sample geometry. Trying to capture all the applications, methods, and hardware encompassed by low-field NMR would be a daunting task and likely of little interest to researchers or industrialists working in specific subject areas. Instead we discuss only a few applications to highlight uses of the hardware and experiments in an industrial environment. For details on more particular methods and applications, we provide citations to specialized review articles.

A rapid measurement of flow propagators in porous rocks

NMR flow propagators have been obtained for brine flowing through Bentheimer sandstone using the rapid DiffTrain pulse sequence. In this way, 8 flow propagators at different observation times Delta were acquired in 67 mins, compared to 7 h for the same measurements implemented with conventional pulsed field gradient (PFG) sequences. DiffTrain allows this time saving to be achieved through the acquisition of multiple displacement probability distributions over a range of Delta in a single measurement. If only the propagator moments are required, this experiment time can be further reduced to 9 mins through appropriate sparse sampling at low q values. The propagator moments obtained from DiffTrain measurements with dense and sparse q-space sampling are shown to be equivalent to those obtained from conventional PFG measurements.

Contributed Review: Nuclear magnetic resonance core analysis at 0.3 T

Nuclear magnetic resonance (NMR) provides a powerful toolbox for petrophysical characterization of reservoir core plugs and fluids in the laboratory. Previously, there has been considerable focus on low field magnet technology for well log calibration. Now there is renewed interest in the study of reservoir samples using stronger magnets to complement these standard NMR measurements. Here, the capabilities of an imaging magnet with a field strength of 0.3 T (corresponding to 12.9 MHz for proton) are reviewed in the context of reservoir core analysis. Quantitative estimates of porosity (saturation) and pore size distributions are obtained under favorable conditions (e.g., in carbonates), with the added advantage of multidimensional imaging, detection of lower gyromagnetic ratio nuclei, and short probe recovery times that make the system suitable for shale studies. Intermediate field instruments provide quantitative porosity maps of rock plugs that cannot be obtained using high field medical scanners due to the field-dependent susceptibility contrast in the porous medium. Example data are presented that highlight the potential applications of an intermediate field imaging instrument as a complement to low field instruments in core analysis and for materials science studies in general.

Corrections of gradiomanometer data for volume fractions in two-phase flows

For typical applications of the gradiomanometer in laboratory two-phase flows, we analyse major contributions to the measured differential pressure. Application for estimation of the fluid-phase volume fraction is valid only when terms representing friction and differential momentum flux (acceleration) are negligible or can be corrected for. The importance of friction is commonly recognized, but that of acceleration in developing flows is less so. Order-of-magnitude estimates of friction and acceleration are given for typical cases of (i) air/water and (ii) kerosene/water two-phase flows. We point out that the acceleration term could be significant in developing liquid/liquid flows of weak density contrast. For the liquid/liquid case, it is therefore important that measurements be made in a fully developed region of the flow. Results for several multi-phase flows are compared with data from local optical fibre probes in a series of companion articles.

Relaxation Analysis of Porous Media at High Magnetic Field Strengths: The Influence of Internal Gradients

The strengths of surface interaction in catalytic materials or wettability in oil‐field reservoir rocks can be assessed based on the ratio of nuclear magnetic resonance (NMR) relaxation times T1/T2. It is often desirable to measure these relaxation times at intermediate or high magnetic field strengths (B0⩾1 T) in order to retain chemical shift information and improve the signal‐to‐noise ratio. However, T2 relaxation is influenced by diffusion through internal magnetic field gradients. These internal gradients, caused by the magnetic susceptibility contrast between liquid and solid, scale with increasing field strength and result in the observation of an effective T2,eff relaxation time. Here, we discuss a method by which the “true” surface relaxivity dominated T2 can be recovered using the example of materials relevant to liquid‐phase catalysis. This method extends the range of magnetic field strengths available for use in porous media studies. We consider the use of T2,eff—T2,eff exchange experiments as...

Probing Multi‐Component Systems in Porous Media Over a Hierarchy of Length‐Scales

Understanding transport processes in porous media is central to the design and operation of many chemical and physical processes. Applications of two magnetic resonance techniques implemented to study the operation of fixed‐bed catalytic reactors are reported here. First, gas and liquid velocity fields within a bead pack is reported, demonstrating that we can now image velocity fields within gas‐liquid‐solid reactors. In a separate experiment, T1‐T2 correlations are shown to gain insight into liquid‐surface interactions within catalyst pellets. The two‐dimensional relaxation time correlation approach is then extended to the implementation of a chemical‐shift (δ)‐resolved T2‐T1‐δ correlation, which has initially been applied to the identification of oil and water fractions in a permeable rock.

Improving Accuracy and Speed of NMR Flow Propagators Measurements in Permeable Rocks

There are two distinct drawbacks to the measurement of fluid flow in porous media using Nuclear Magnetic Resonance (NMR) flow propagators. First, spin relaxation impairs the quantitative nature of the data. Second, the experiments can be considerably time consuming since both the Pulsed Field Gradient (PFG) strength g and observation time Δ need to be varied independently. Here we present two separate solutions to these problems and show how they can be applied to the study of fluid flow in permeable reservoir rocks. The accuracy of the measurements can be improved using a combination of ζ−T2 and T1−T2 correlations. Under certain ideal conditions it is possible to use these data to remove both the T1 and T2 relaxation weighting from flow propagators [Mitchell et al. J. Magn. Reson. DOI:10.1016/j.jmr.2008.05.001 (2008)]. Statistical analysis of the resultant probability density distributions yields observed mean displacements 〈ζ〉 equal to the expected mean displacements 〈ζ〉0. If speed is more important tha...