The aggregation of clay particles in aqueous solution is a ubiquitous everyday process of broad environmental and technological importance. However, it is poorly understood at the all-important atomistic level since it depends on a complex and dynamic interplay of solvent-mediated electrostatic, hydrogen bonding, and dispersion interactions. With this in mind, we have performed an extensive set of classical molecular dynamics simulations (included enhanced sampling simulations) on the interactions between model kaolinite nanoparticles in pure and salty water. Our simulations reveal highly anisotropic behavior, in which the interaction between the nanoparticles varies from attractive to repulsive depending on the relative orientation of the nanoparticles. Detailed analysis reveals that at large separation (>1.5 nm), this interaction is dominated by electrostatic effects, whereas at smaller separations, the nature of the water hydration structure becomes critical. This study highlights an incredible richness in how clay nanoparticles interact, which should be accounted for in, for example, coarse-grained models of clay nanoparticle aggregation.
Carefully engineering the size distribution of bridging solids should enable us to form filter cakes of low permeability. A theory called the ideal packing theory is commonly used to blend bridging solids which suggests the ideal blend of particles should follow the relationship cum vol% ∝ dx. The aim of this work was to experimentally assess this theory. Investigations were carried out to determine if there is an x value which gives a better fluid loss performance than the typically-used x = 0.5. The results suggest that selecting x ~ 1 could be more appropriate than using the conventional x = 0.5. The physical meaning when x = 1 is that there will be an equal volume of particles of each size within the distribution; i.e. the distribution is linear. In addition, the results also showed that a blend with a broad size distribution gave a lower fluid loss than a narrow distribution, even when the narrower distribution consisted of finer particles. The trend was that filter cakes of decreasing permeability were formed as x increased from 0.1 to 0.5. Further increase in x up to 1.25 did not appear to have a prominent effect, while further increases beyond 1.25 appeared to increase the filter cake permeability. Trends were similar for filter cakes formed on filter paper and on simulated rock material. Particle blending is important for the selection of bridging solids for drill in fluids, and also for wellbore strengthening (stress cage) applications. Conventional ideal packing theory has been widely used but a review of this theory backed up by laboratory checks has been overdue. This work should aid in the development of a more consistent approach to the selection of the optimum blend of bridging material for a given application.
The effectiveness of polymeric flocculant addition and hydrodynamics on increasing the critical permeation flux, J crit , during crossflow microfiltration of bentonite suspensions using a tubular ceramic membrane module was investigated. The investigation determined the effects of flocculant concentration on J crit at various crossflow velocities. The best filtration performance (highest J crit ) was obtained at a flocculant dose of 500 mg kg -1 (mg of flocculant per kg of solids) and at a crossflow velocity of 1.71 m s -1. Particle size has been used as a parameter to fit the shear-induced hydrodynamic diffusion model to the experimental filtration data.
Summary We propose an experimental approach to evaluate how typical fluids influence shale dispersion. In this approach, finely ground shale is left to settle in the fracturing fluid, generating particle-size and concentration profiles within the settling column. Samples are taken at various settling times and depths and then analyzed with regard to turbidity and capillary-suction-time (CST) behavior. Particle-size-distribution (PSD) measurements are used to further substantiate analysis. Turbidity data indicate the volume of particles present, and PSD data indicate the sizes of these particles (or flocs). This approach was tested using ground shale, Eagle Ford brine (EFB), and three typical fluid additives. Without additives present, shale flocculation resulted in rapid particle settling, and samples taken from suspension gave low turbidity and CST values. With additives present, suspensions were better dispersed and hence tended to give higher CST values. Some additives hindered flocculation more effectively than others. The results suggest that low CST numbers might not always be desirable; additives that are good inhibitors might hinder flocculation of shale particulates and hence promote higher CST numbers. In this paper we discuss how our proposed experimental approach can give insights into the influence of additives on the degree and nature of shale dispersion.
The constant pressure filtration characteristics of cellulose fibers, titania (rutile) and mixtures of the two were studied using an automated filtration apparatus. With filtrations at 450 kPa, the average permeability (k av ) for pure fiber and rutile were approximately 3.2 × 10 -17 and 1.3 × 10 -16 m 2 , respectively, with the variation of k av with fiber fraction showing a maximum. Similar trends were observed at filtration pressures of 150 and 600 kPa. The porosities (e av ) of filter cakes formed from pure fiber and rutile suspensions were approximately 0.75 and 0.6, respectively. Interparticle penetration and additive porosity models were applied to the porosity data, and the additive porosity model appeared to better represent the experimental data. Also, the results obtained suggest that abrupt transitions in cake structure occur part way through some filtrations, resulting in anomalous filtration behavior.
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