Porous polymer films cast from latex-glucose dispersions

Macroporous films of glassy polymer are prepared from stable aqueous dispersions of latex with dissolved glucose, coated on a carrier substrate and dried at elevated temperature to a hybrid film, followed by water immersion to leach out the glucose and any redispersible latex. Temperature and time of drying must be tailored to facilitate local coalescence of latex particles by glucose expulsion while avoiding complete demixing of the two phases. The conditions for which mutual interpenetration of locally film-formed latex and glucose networks can be kinetically locked-in to maximize film yield and porosity are elucidated as a function of glucose/latex content. The porous films were analyzed gravimetrically and by UV-vis spectroscopy and scanning electron microscopy. They possess a disordered connected network of sub-micron pores graded in the film thickness direction, with accessibility decreasing from upper to lower surface due to upward transport of mobile glucose by capillarity and convection

Systematic pore-scale study of low salinity recovery from Berea sandstone analyzed by micro-CT

The low salinity effect in clay-rich outcrop sandstones is probed by micro-CT imaging and analysis. A set of eight Berea sandstone mini-plugs underwent primary drainage and aging in crude oil to a mixed-wet state, followed by spontaneous imbibition of high and low salinity brines and imaging of this sequence of prepared starting and endpoint states. Tomogram registration and analysis were used to determine the salinity-induced changes in oil volume, oil/rock and oil/brine interfacial areas, and oil/brine interfacial mean curvature. Pore-scale statistics were extracted to explore any local correlation between the low salinity effect and pore geometry/topology. The qualitative observations and quantitative analyses demonstrated that the small oil recovery by the low salinity effect corresponded to a slight shift towards water-wet.Financial support from the member companies of the Digital Core Consortium Wettability Satellite and Statoil are acknowledged

Physics and mathematics of interfaces in self-assemblies : studies in electrostatics and triply periodic minimal surfaces

The key to theoretical prediction of the behaviour of self-assembling systems is an understanding of structure. This structure is the global spatial manifestation of the sum of all local interactions. As a consequence of the subtlety of this connection, prediction of structure from the basis of a detailed model of the specific molecular interactions is not feasible, as our mathematical limitations force the imposition of strict geometrical assumptions. Instead, such physical treatments are sacrificed for the freedom of description offered by simplified geometrical approaches. In this thesis two examples of such geometrical motivations, of particular reference to the phases observed in binary surfactant-water mixtures, are analysed and extended. Helfrich attributed the energy cost of fluctuation of the surfactant aggregate to the bending of the interface separating the hydrophilic and hydrophobic regions, and proposed a simple curvature energy function describing this. Applying simple stability considerations, we find that this functional form cannot be reconciled with the intuition of a preferred interfacial curvature, and propose an alternative phenomenological description which is consistent with this notion and with existing continuum models of the surfactant film. For the specific case of preferentially flat films (that is, zero spontaneous curvatures) the surfactant bilayers have a tendency to form lamellar phases, which exhibit interesting behaviour attributed to the bending energy. To investigate this, we calculate this energy directly for the specific case of ionic surfactants in aqueous electrolytes, thus permitting the inference of formulae for the bilayer bending modulus (characterising its degree of stiffness). Perhaps the most striking structural feature of surfactant-water systems is the observation of bicontinuous phases. The partitioning interface in these formations is found to be modelled in many cases by the class of triply periodic minimal surfaces. Here we derive new examples of these special surfaces and present an algorithm for the parametrisation of this class, thus facilitating a quantitative assessment of the degree to which these surfaces match the real surfactant interface

Added insight from image-based wettability characterization

Microtomographic rock and fluid imaging under in-situ conditions is applied for reservoir wettability characterization. The investigation entails careful sample preparation and cleaning of mini-plugs, operation with reservoir fluids, wettability restoration, centrifuge wettability testing cycles, repeated sample scanning and image analysis, parametrization of wettability and digital rocks simulation for input into reservoir modeling. The results are compared to conventional Amott testing performed in core laboratories. Determination of saturations from image analysis, instead of centrifuge production, allows the use of stock tank crude, rather than exchanged mineral oil. Doping of the synthetic formation water (here with 1 M sodium iodide) was applied for enhancement of the X-ray contrast. The digital imaging workflow offers insight on the liquid distributions from the plug scale down to the pore-scale, linked to applied pressure gradients and resulting pore fluid occupancies in the sequence of displacement states. An example is given with the investigation of a North-German oil field, where the image-based workflow led to a revised view of the reservoir conditions for spontaneous imbibition and drainage, and the overall wetting behavior

Techniques in helical scanning, dynamic imaging and image segmentation for improved quantitative analysis with X-ray micro-CT

This paper reports on recent advances at the micro-computed tomography facility at the Australian National University. Since 2000 this facility has been a significant centre for developments in imaging hardware and associated software for image reconstruction, image analysis and image-based modelling. In 2010 a new instrument was constructed that utilises theoretically-exact image reconstruction based on helical scanning trajectories, allowing higher cone angles and thus better utilisation of the available X-ray flux. We discuss the technical hurdles that needed to be overcome to allow imaging with cone angles in excess of 60°. We also present dynamic tomography algorithms that enable the changes between one moment and the next to be reconstructed from a sparse set of projections, allowing higher speed imaging of time-varying samples. Researchers at the facility have also created a sizeable distributed-memory image analysis toolkit with capabilities ranging from tomographic image reconstruction to 3D shape characterisation. We show results from image registration and present some of the new imaging and experimental techniques that it enables. Finally, we discuss the crucial question of image segmentation and evaluate some recently proposed techniques for automated segmentation

Removal of crude oil from kaolinite by water flushing at varying salinity and pH

The ability of crude oil to adhere to kaolinite in an aqueous environment by adsorbing or depositing its polar components (asphaltenes and resins), and the ability of subsequent water flushing to remove this bound oil, were compared for two oils and varying salinity and pH of the flushing solution. A scanning electron microscopy technique was used to image the locations of oil residues on and between kaolinite platelets, while fluorescence spectroscopy yielded the corresponding amount of asphaltenics. Consideration of the mechanisms of electrostatic interfacial attraction and surface precipitation giving rise to the adsorption/deposition of asphaltenics on kaolinite were used to interpret the extent of their removal by flushing. The oil exhibiting greater surface precipitation was fairly unresponsive to flushing, with displacement of the bulk oil leaving residues substantially lining the kaolinite platelets and filling the pores between them. The oil which adsorbed by electrostatic attraction was more amenable to removal of residues, to partially reinstate the water-wetness of the pristine kaolinite, by flushing with salt solutions which weakened this attraction. In particular, higher salinity of the flush minimized the attractions between oppositely charged sites on the heterogeneous interfaces, and pH shift to higher or lower levels rendered the interfacial charges more similar and mutually repulsive

Experimental investigation of deposition of crude oil components in brine-filled pores

It is often presumed that fine-scale surface pores and roughness in reservoir rock remain water-wet. To test this assumption, deposition tendency of asphaltenes and resins during crude oil aging of brine-filled pores was investigated. Model frameworks o

Effect of Water Salinity and pH on the Wettability of a Model Substrate

While the wettability of oil reservoirs has been the focus of many studies, little is known as to whether, and to what extent, the wettability evolves during oil recovery by waterflooding. To this end, a model silicate substrate, namely glass, was treated by oil drainage of the surrounding salt solution and aging (representing the initial state), followed by oil displacement by a second salt solution (flooded state). The two states were analyzed by scanning electron microscopy of the oil components attached to the substrate and measurement of their influence on macroscopic contact angles. Initial-state wettability took the form of an incomplete asphaltenic film interrupted by nanoscale channels and pockets of trapped salt solution. The film was observed to remain fluidic and, on flooding, could retract and detach to leave a more incomplete coverage, usually of oil nanodroplets. The influence of pH of the initial and flooding solutions on these two states was generally opposite; high pH, at which oil–substrate repulsion is prevalent, tended to reduce film coverage in the initial state but aid its retention by the substrate on flooding. Contact angles on flooded substrates depended on this residual adhering nanoscale oil and on the ability of bulk oil to adhere by reconnecting to it. Again, the pH dependence of these two factors was opposite. The results suggested a possible supplementary mechanism for enhanced recovery by low salinity flooding

Wettability alteration of kaolinite exposed to crude oil in salt solutions

Adsorption and deposition of polar components of crude oils onto kaolinite in the presence of aqueous solutions of sodium and calcium chlorides is probed by spectroscopy, microscopy and drop contact angle. The fine kaolinite particles are thinly coated onto glass to remain immobile during the aging in salt solution and oil, and subsequent solvent rinsing. These thin coats facilitate quantification of the extent of deposition versus salt composition, while also allowing high-resolution microscopy of its spatial distribution. The asphaltene-based deposits take the form of nanoparticle aggregates decorating kaolinite faces and edges. At low salinity and low-neutral pH, water surrounding kaolinite is expelled by oil deposition and pore penetration to strongly alter wettability of the aggregate from hydrophilic to oleophilic, and trends are in qualitative agreement with expectations from DLVO theory. Higher ionic strength suppresses oil deposition, either by limiting it to kaolinite edges in the case of sodium chloride-rich solutions or protecting both faces and edges at high calcium chloride contents. Only the latter suffices for the kaolinite aggregate to substantially retain its hydrophilicity