Bryce MacMillan

Using Magnetic Resonance Imaging and Petrographic Techniques to Understand the Textural Attributes and Porosity Distribution in Macaronichnus-Burrowed Sandstone

ABSTRACT Magnetic resonance images are paired with petrographic data to evaluate the textural characteristics of rocks dominated by Macaronichnus segregatis, a trace fossil that is commonly associated with rocks deposited in shallow, marginal marine sedimentary environments. MRI techniques used revealed the three-dimensional geometry of the trace fossil. Burrows are typically horizontal and in plan view range between straight, sinuous, meandering, and spiral geometries. Changes in burrow morphology may be related to population density and patchy resource distribution. The pairing of MRI and petrographic data helped map the distribution of porosity in the burrowed rock. Because MRI images represent complex composites of nuclear spin density and MR relaxation times, each of which is related to pore size, stronger MR signals must be calibrated to known porous zones by integrating petrographic data with MR data. The complex distribution of porosity and its relationship to the matrix show that this fabric represents a dual porosity-permeability system and may affect the resource (reservoir or aquifer) quality of similarly burrowed sedimentary rocks. Future research should elaborate upon the porosity-permeability model for this and similar fabrics.

An n.m.r. investigation of the dynamical characteristics of water absorbed in Nafion

Proton and deuterium spin–lattice relaxation times (T1), spin–spin relaxation times (T2), and rotating frame spin–lattice relaxation times (T1ρ) and Fluorine T1 and T2 were measured as a function of hydration and temperature in hydrated Nafion. The proton and deuterium data display an apparent dynamical transition which we have attributed to a change in the degree of order within the aqueous phase. The temperature at which this transition occurs, Tt, is a function of the level of hydration, increasing for decreasing hydration. Above Tt, the relaxation processes are similar to those observed in bulk water.

Visualizing the Internal Physical Characteristics of Carbonate Sediments with Magnetic Resonance Imaging and Petrography

ABSTRACT Magnetic resonance (MR) images are analyzed in conjunction with petrographic data to evaluate the textural characteristics of rocks dominated by fabric-selective dolomitization. The magnetic resonance imaging (MRI) measurements reveal the three-dimensional geometry of the physical sedimentary structures and the trace fossils that influenced dolomitization and porosity development. Because MRI images represent composites of nuclear spin density and MR relaxation times, each of which can be related to pore size, stronger MRI image intensity must be calibrated to know porous zones by integrating petrological data with MR data. Pairing of MR images with petrography helps map the distribution of porosity in diagenetically altered rock. The data presented herein show the potential of a new class of MRI technique as an imaging tool for low-porosity rocks. The results demonstrate that MRI technology can significantly enhance petrological studies. Notable results include 1) the successful resolution of the porosity distribution in carbonate rocks characterized by low porosity (generally less than 6%); 2) the successful acquisition of the three-dimensional data required to model the porous network; and 3) recognition that the complex distribution of porosity and its relationship to the matrix show that this fabric represents a dual porosity/permeability system and may reduce the resource quality of similary burrowed carbonate rocks. End_Page 363------------------------

N.m.r. relaxation in Nafion—the low temperature regime

Abstract The dynamical characteristics of water absorbed in Nafion are investigated using n.m.r. At temperatures below the dynamical transition temperature, T t , relaxation rates indicate mobility associated with a fluid but the derived motional activation energies are similar to those of ice. This indicates a well ordered supercooled fluid consisting of hydrogen bonded water structures. The correlation time τ c is found to have a Gaussian dependence on the surface area to volume ratio, unlike simple porous systems. We have shown that the surface area depends on r 2.5 . We feel that this is due to the irregular nature of the surfaces of the clusters.

Spatial and temporal mapping of water content across Nafion membranes under wetting and drying conditions.

Water transport and water management are fundamental to polymer electrolyte membrane fuel cell operation. Accurate measurements of water content within and across the Nafion layer are required to elucidate water transport behavior and validate existing numerical models. We report here a direct measurement of water content profiles across a Nafion layer under wetting and drying conditions, using a novel magnetic resonance imaging methodology developed for this purpose. This method, multi-echo double half k-space spin echo single point imaging, based on a pure phase encode spin echo, is designed for high resolution 1D depth imaging of thin film samples. The method generates high resolution (<8 microm) depth images with an SNR greater than 20, in an image acquisition time of less than 2 min. The high temporal resolution permits water content measurements in the transient states of wetting and drying, in addition to the steady state.

High pressure magnetic resonance imaging with metallic vessels.

High pressure measurements in most scientific fields rely on metal vessels given the superior tensile strength of metals. We introduce high pressure magnetic resonance imaging (MRI) measurements with metallic vessels. The developed MRI compatible metallic pressure vessel concept is very general in application. Macroscopic physical systems are now amenable to spatially resolved nuclear magnetic resonance (NMR) study at variable pressure and temperature. Metallic pressure vessels not only provide inherently high tensile strengths and efficient temperature control, they also permit optimization of the MRI RF probe sensitivity. An MRI compatible pressure vessel is demonstrated with a rock core holder fabricated using non-magnetic stainless steel. Water flooding through a porous rock under pressure is shown as an example of its applications. High pressure NMR spectroscopy plays an indispensable role in several science fields. This work will open new vistas of study for high pressure material science MRI and MR.

Moisture migration in starch molding operations as observed by magnetic resonance imaging

Abstract Magnetic resonance imaging was an effective means for visualizing moisture profiles during drying of starch molded confectionery, and clearly demonstrated the importance of moisture transfer between the confectionery gel and the molding starch. Rapid formation of a very dry “skin” was observed that resulted in case-hardening. Drying was effectively diffusion controlled after the first 30 min. Moisture profiles within the porous bed of molding starch, where total proton density is low and T 2 * is short, were visualized using single point ramped imaging with T 1 enhancement (SPRITE). Similar images were not possible using more traditional spin-echo techniques. The long component of a bi-exponential T 1 was linearly related to the solids content, and T 1 –null images were constructed to visualize iso-solids contour lines.

Analysis of Syneresis of HPAm/Cr(II) and HPAm/Cr(III) Acetate Gels Through 1H Nuclear Magnetic Resonance, Bottle Testing, and UV-vis Spectroscopy

Abstract Polymer solutions with 7500 mg/L of partly hydrolyzed polyacrylamide were crosslinked with Cr(III) acetate 50% active, Cr(III) acetate hydroxide, and Cr(II) acetate respectively. A syneresis-inducing polymer to crosslinker weight ratio of 5/1 was employed. An empirical correlation was found between 1H NMR data and gel syneresis. Chromium speciation indicated that at the experimental conditions used aging the gels did not favor the oxidation of Cr(II) or Cr(III) to Cr(VI). The polymer solution crosslinked with Cr(III) acetate 50% active behaved similar to that cross-linked with Cr(III) acetate hydroxide.

1H NMR Characterization of HPAm/Cr(III) Acetate Polymer Gel Components

Abstract Low-field 1 H nuclear magnetic resonance (NMR) was used to characterize the components of polymer gels formulated with partly hydrolyzed polyacrylamide (HPAm) and Cr(III) acetate. Changes in the NMR relaxation times were used to characterize samples of polymer, cross-linker, polymer solutions, and cross-linker solutions in bulk and in porous media. The results obtained indicated that changes of HPAm concentration do not have a significant effect on the relaxation times, while changes in Cr(III) acetate concentration do. Therefore, the concentration of cross-linker is the most critical variable in the process of characterizing HPAm/Cr(III) acetate polymer gels using low-field 1 H NMR.

Mapping three-dimensional oil distribution with π-EPI MRI measurements at low magnetic field.

Magnetic resonance imaging (MRI) is a robust tool to image oil saturation distribution in rock cores during oil displacement processes. However, a lengthy measurement time for 3D measurements at low magnetic field can hinder monitoring the displacement. 1D and 2D MRI measurements are instead often undertaken to monitor the oil displacement since they are faster. However, 1D and 2D images may not completely reflect the oil distribution in heterogeneous rock cores. In this work, a high-speed 3D MRI technique, π Echo Planar Imaging (π-EPI), was employed at 0.2T to monitor oil displacement. Centric scan interleaved sampling with view sharing in k-t space was employed to improve the temporal resolution of the π-EPI measurements. A D2O brine was employed to distinguish the hydrocarbon and water phases. A relatively homogenous glass bead pack and a heterogeneous Spynie core plug were employed to show different oil displacement behaviors. High quality 3D images were acquired with π-EPI MRI measurements. Fluid quantification with π-EPI compared favorably with FID, CPMG, 1D-DHK-SPRITE, 3D Fast Spin Echo (FSE) and 3D Conical SPRITE measurements. π-EPI greatly reduced the gradient duty cycle and improved sensitivity, compared to FSE and Conical SPRITE measurements, enabling dynamic monitoring of oil displacement processes. For core plug samples with sufficiently long lived T2, T2(∗), π-EPI is an ideal method for rapid 3D saturation imaging.