Andrew Fogden

Adhesion of Oil to Kaolinite in Water

Uniform coats of kaolinite particles on a flat glass substrate were prepared to be sufficiently smooth and thin to allow reliable measurement of contact angles of captive crude oil drops in a range of salt solutions, without any particle removal. The contact angle hysteresis was used to infer the extent of oil adhesion via rupture of the intervening water film and anchoring of charged groups to kaolinite. For sodium chloride solutions, adhesion decreases monotonically with pH and/or salinity, with strong adhesion only manifested under acidic conditions with salinity at most 0.1 M. Calcium chloride solutions at pH around 6 switch from strong adhesion in the range 0.001-0.01 M to weak adhesion at higher concentrations. For all mixtures of sodium and calcium chlorides investigated, a total ionic strength above 0.1 M guarantees a weak adhesion of oil to kaolinite. Results are qualitatively consistent with theoretical expectations of electrostatic interactions, with H(+) and Ca(2+) being potential-determining ions for both interfaces.

Patterned Wettability of Oil and Water in Porous Media

The microscopic wettability state of porous media, based on glass bead packings, after crude oil drainage of brine was investigated using X-ray micro-CT, white-light profilometry, and electron microscopy. Tomography revealed that the bulk residual brine occupied around 10% of void space, located in smaller pores and as pendular rings around bead contacts, in agreement with numerical simulations of drainage. The bead packing contained planar slabs of mica, quartz, and oxidized silicon wafer, which after flushing and disassembly of the pack allowed analysis of their wettability alteration due to deposition of asphaltenes from the crude oil. These substrates exhibited an overall pattern of rings with clean interiors, matching the brine pendular ring size inferred from experimental and simulated drainage, and asphaltene deposition in their exteriors, verifying the mixed wet model of oil reservoir wettability. The extent of asphaltene intrusion into ring interiors and completeness of asphaltene coverage of exteriors both increased with overall deposition tendency for the brine composition. The observed dependence on NaCl concentration and pH was consistent with expectations from DLVO and non-DLVO interactions governing brine thin film rupture and subsequent asphaltene deposition.

Pore-Scale Imaging of Oil and Wettability in Native-State, Mixed-Wet Reservoir Carbonates

3D pore-scale imaging and analysis provides an understanding of microscopic displacement processes and potentially a new set of predictive modeling tools for estimating multiphase flow properties of core material. Reconciliation and integration of the data derived from these models requires accurate characterization of the pore-scale distribution of fluids and a more detailed understanding of the role of wettability in oil recovery. The current study reports experimental imaging progress in these endeavors for a preserved-state carbonate core from a Middle Eastern waterflooded reservoir. Micro-CT methods were used in combination with novel fluid X-ray contrasting techniques and image registration to visualize the 3D pore-scale distribution of residual oil in mini-plugs. Segmentation of the registered tomograms and their differences facilitated estimation of the residual oil saturation. These predictions from digital analysis agreed reasonably well with laboratory measurements of oil saturation from extraction of sister mini-plugs and spectrophotometry. The tomogram segmentations provide additional information beyond this average value, such as the fractions of oil associated with macroporosity and microporosity. After the tomogram acquisitions, one of the dried mini-plugs was cut and SEM imaged at this exposed face to provide 2D images of fine features below the micro-CT resolution limit, such as the characteristic dimpled texture of asphaltene films on calcite surfaces due to their local wettability alteration in the reservoir. A new registration procedure was developed to embed the SEM images from the cut plug into the tomogram of the original uncut plug at their correct locations, so that this high-resolution wettability information could be integrated into the 3D pore network description and correlated to the local distribution of residual oil.

Bending rigidity of ionic surfactant interfaces with variable surface charge density: the salt-free case

The theoretical understanding of the electrostatic contribution to the bending constants of ionic surfactant interfaces has been extensively developed over the past decade. In this contribution, we deal with systems without added electrolyte, and allow for the interfacial charge density to vary with curvature, treating both an undulating sheet geometry and a spherical/cylindrical cell model. The rippled-plane case shows that the lowest free energy state is that for which the surface potential remains fixed, i.e. a conducting interface. Moreover, the deduced expression for the bending modulus agrees with that derived from the cell model, generalizing our previous result that the bending modulus is geometry-independent, even for systems without added salt, to cases where the surface charge is permitted to redistribute on bending.

On the formation and structure of nanometric polyhedral foams: toward the dry limit.

High surface area, high porosity, nanometric polygonal silica foams with hierarchically connected and uniformly sized pore systems are reported here. We observe a remarkable increase in foam cell sizes from mesoscopic to macroscopic dimensions upon swelling the self-assembled template with oil. The resultant structures resemble classical macroscopic soap foams and display, among other features, Plateau borders and volume fractions approaching the dry limit of 100%. In well-developed foams of this kind, dimensionally isometric polyhedral cells are connected by relatively short, flat cylindrical mesopores through polyhedral faces and micropores through the walls. For one sample, with approximately 75 nm diameter primary foam cells, we infer three separate sets of cell-connecting mesopores puncturing tetragonal, pentagonal, and hexagonal faces of the component polyhedra. A multiple step model of foam formation is discussed where an organic silica precursor progressively hydrolyzes and condenses as a growing flexible shell from the core-corona interface of oil-swollen triblock copolymer micelles or microemulsion droplets, inducing a clouding phenomena in the otherwise stabilizing poly(ethylene oxide) chains, leading to aggregation, deformation, and jamming to high volume fractions.

Silica-cast replicas for morphology studies on spruce and birch xylem

Sol-gel mineralization has been used and evaluated as a tool for morphological studies on Picea abies and Betula verrucosa. Wood specimens and a pulped spruce sample were impregnated with a silica sol-gel and subsequently heated (calcined) to condense the surfactant-templated polysilicic acid into structured mesoporous silica. During this calcination process, the wood substance and the surfactant were removed and a silica-cast replica of the sample was obtained. The sol-gel mineralization method produced replicas that were studied by environmental scanning and transmission electron microscopy (ESEM, TEM) without additional sample preparation. The calcination induced some shrinkage above the fiber level, but the ultrastructural dimensions were not discernibly affected. The silica-cast replica method may therefore be a useful tool for studies of the wood ultrastructure, including the cell-wall pore structure (microcavities), down to the nanometer level.

3D Imaging of the Pore Network in the Shuaiba Reservoir, Al Shaheen Field

ment and simulation of flow properties. As a complement to parallel studies of the plugs by conventional petrographic and core analysis techniques, a set of samples from four wells in the Shuaiba reservoir of the Al Shaheen field was analysed by 2D mineral mapping (from QEMSCAN) of polished plug sections, and by 3D tomographic mapping (from micro-CT) of subsampled mini-plugs, as a complement to parallel studies of the plugs by conventional petrographic and core analysis techniques. QEMSCAN showed a high variability in measured porosity and pyrite content over all sampled length scales, from millimetres (across the polished plug faces) to feet (with depth in a given well) to kilometres (across the four wells). The porosity from QEMSCAN was generally found to be in good agreement with that measured on the conventional plugs. Two mini-plugs of 5 mm diameter were scanned using helical micro-CT, one of which was subsequently analysed to segment the macropores, microporosity, calcite and pyrite. Comparison with the QEMSCAN results from the section of the “parent” plug showed consistency in estimated porosity and pyrite content between the two methods. Simulations of conductivity and absolute permeability were performed on subvolumes of the segmented tomogram, and displayed a strong variability with the location and size of the chosen subvolume, although the overall trends remained in good agreement with core analysis.

Rheology and surface tension of water-based flexographic inks and implications for wetting of PE-coated board

This doctoral thesis comprises three studies dealing with water-based flexography on polymer-coated boards, which have been presented in the five papers included at the end of the thesis. The first study (covered in three papers) presents results from characterisation of a matrix of water-based inks with respect to their rheology, surface tension, wetting, and fulltone printing performance on PE-coated board. The commercial water-based inks used vary in type of pigment and acrylic vehicle, and in pigment/vehicle mixing proportions. For all mixing proportions, the inks were shear thinning, with viscosity increasing strongly with content of solution (versus emulsion) polymer in the vehicle. Increasing amount of solution polymer also gave the indirect consequence of lower surface tension values. The wet ink amount transferred to the board and the resulting print uniformity responded sensitively to ink formulation and could be correlated to the corresponding changes in these two ink properties. Transferred amount correlated well with ink plastic viscosity and static surface tension, exhibiting a maximum at intermediate values of both. Print mottle decreased with increasing content of solution polymer, principally due to the associated increase in low-shear viscosity and decreased surface tension, both serving to reduce substrate dewetting. In the second study, the effect of corona discharge treatment of PE-coated board on its surface chemistry and print resistance properties was evaluated. The increase in total surface energy, due to its polar component, with increasing corona level was strongly correlated to surface oxidation fraction from XPS. AFM revealed oxidised material nano-mounds, which increased in size and substrate coverage with corona level. Wet rub resistance (with water) first increased for lower corona dosages before decreasing at higher dosages. This worsened water resistance at higher dosages is presumably due to the oxidised material dissolved and dispersed in the ink film. The third study presents results from another set of water-based acrylic inks printed on boards coated with PE, OPP and PP. Print quality and resistance properties, though dependent on the polymer type, were strongly influenced by the choice of emulsion polymer and presence of silicone additive in the vehicle, with corona treatment level playing a lesser role. The emulsion polymer giving best resistance performance was generally found to give poorest press performance and visual appearance. Again the trends could be understood in terms of wet ink surface tension (versus substrate surface energy), dictating print uniformity, and dry print surface energy (and swellability), dictating resistance properties.

Influence of formulation and properties of water-based flexographic inks on printing performance for PE-coated board

In this study the flexographic printing of low-density polyethylene- (LDPE-) coated liquid packaging board is analysed for a range of water-based inks, varying in type of pigment and acrylate-polym ...

Acoustic characterisation of film splitting in a HSWO printing nip

An acoustic technique for investigation of ink film splitting was further developed and applied to monitor printing of light weight coated (LWC) papers on a heat-set web offset (HSWO) press. The ...