OBSERVATION AND MODELLING OF FLUID TRANSPORT INTO POROUS PAPER COATING STRUCTURES

Merged with duplicate record 10026.1/581 on 14.03.2017 by CS (TIS)In paper printing, one of the most important aspects for consideration is the control of ink setting rate. Ink setting, depending on ink and press type, is a function of evaporation, curing and removal of the liquid phase by capillary mechanisms steered by the porous substrate. In most cases, absorption by the substrate is the dominating mechanism. Many paper or board substrates are coated with a layer of pigment panicles and binders. It is recognised that the void network between these panicles has the most important influence on the absorption dynamics. Many aspects of liquid absorption into porous networks are poorly understood. It is shown that it is necessary to characterise both the pore-level structure and the permeability of the network simultaneously. To remove indeterminate effects caused by the usually uneven thin layers of coatings adopted in practice, a novel methodology was developed in this work comprising of a range of unique techniques such as the formation of porous tablet-like blocks of CaC03. By applying variable compression forces to a compact of line-ground mineral, a wide range of usable porosities were obtained whilst keeping the surface chemistry and skeletal-defined pore geometry constant. The samples were characterised using mercury porosimetry. The methodology included techniques to study interactions of the structures with industrially and environmentally relevant liquids. An Ink-Surface Interaction Tester (ISIT) was used to analyse ink setting behaviour as a dynamic measure of ink rheology and solids content. This device was modified to provide a measure of the time-dependent extensional strain that is applied to the ink layer in addition to the normally obtained ink tack force values. The importance of the inertial flow regime beyond that of pure viscous flow and its impact in an interconnected network structure, where liquid does not imbibe continuously in a steady laminar flow behaviour at the wetting front, are demonstrated. Mechanisms are proposed which account for the uneven wetting line and its action in leaving parts of the pore network unfilled. Along with other findings, deviations from Lucas-Washburn (LW) scaling are elucidated. These findings are discussed in the context of paper printing and give direction for developing beyond the current limits encountered using environmentally friendly minerals and ink constituents.Omya AG, Oftringen, Switzerlan

Synchrotron-based pore-network modeling of two-phase flow in Nubian Sandstone and implications for capillary trapping of carbon dioxide

Depleted oil fields in the Gulf of Suez (Egypt) can serve as geothermal reservoirs for power generation using a CO2-Plume Geothermal (CPG) system, while geologically sequestering CO2. This entails the injection of a substantial amount of CO2 into the highly permeable brine-saturated Nubian Sandstone. Numerical models of two-phase flow processes are indispensable for predicting the CO2-plume migration at a representative geological scale. Such models require reliable constitutive relationships, including relative permeability and capillary pressure curves. In this study, quasi-static pore-network modelling has been used to simulate the equilibrium positions of fluid-fluid interfaces, and thus determine the capillary pressure and relative permeability curves. Three-dimensional images with a voxel size of 0.65 micro m3 of a Nubian Sandstone rock sample have been obtained using Synchrotron Radiation X-ray Tomographic Microscopy. From the images, topological properties of pores/throats were constructed. Using a pore-network model, we performed a sequential primary drainage-main imbibition cycle of quasi-static invasion in order to quantify (1) the CO2 and brine relative permeability curves, (2) the effect of initial wetting-phase saturation (i.e. the saturation at the point of reversal from drainage to imbibition) on the residual-trapping potential, and (3) study the relative permeability-saturation hysteresis. The results improve our understanding of the potential magnitude of capillary trapping in Nubian Sandstone, essential for future field-scale simulations. Further, an initial basin-scale assessment of CO2 storage capacity, which incorporates capillary trapping, yields a range of 14-49 GtCO2 in Nubian Sandstone, Gulf of Suez Basin

Capillary Pressure in Nanopores: Deviation from Young-Laplace Equation

Recent studies on multi-phase fluids in nanoscale capillaries indicated that the capillary wall-fluid interactions could play a dominant role on the co-existence of the phases, which caused the fundamental properties of the fluids, such as density, viscosity, and interfacial tension, to become capillary size-dependent. At the extreme of the confinement, these properties become vague. This raises a serious question on the validity of Young-Laplace equation to predict capillary pressure in small capillaries that the unconventional resources commonly exhibit. In this research, using non-equilibrium molecular dynamics simulation of mercury injection into model nano-capillaries, the nature of multi-phase fluids is investigated in capillaries with sizes below 20 nm and the Young-Laplace equation is re-visited. Higher capillary pressure is predicted for the model nano-capillaries used in the simulations compared to that value obtained using the Young-Laplace equation, in particular, when the capillary diameter is less than 10nm. Good agreement found with the theory in larger size capillary. The capillary pressure increases as the capillary size decreases and shows a power-law dependence on the size of the capillary. This dependence yields up to 70% increase in the estimated capillary pressure value for the extreme case of 1nm capillary. Higher tangential local pressure resulted from the adsorption phase, which identified as the cause of this difference. Two approaches were used for the capillary pressure calculation from the molecular dynamics simulation and the more reliable one was used for further evaluation. Based on the observations, a modified Young-Laplace equation is proposed for mercury-air filled pore systems which are commonly used in Mercury Injection Capillary Pressure (MICP) experiments for the pore volume and pore size distribution (PSD) measurements. At the highest injection pressure of MICP, the minimum captured pore throat size is predicted 4.8nm instead of 3.6nm based on the Young-Laplace equation. The increase in the predicted capillary size leads to an increase in total pore volume of the sample. The error is up to 20% for measurements with shale samples. The results are important for the characterization of resource shale formations because the pore volume correction influence the hydrocarbon in-place and reserve calculations. The work can be extended to other multi-phase systems, such as oil-water and water-gas, grouping with other capillary wall material to study the behavior of multi-phase flow in nano-capillaries

ENVIRONMENTALLY FRIENDLY TECHNOLOGY: THE BEHAVIOUR OF NATURAL AND SYNTHETIC BINDER SYSTEMS WITHIN PAPER COATINGS

Coating shrinkage upon drying is a phenomenon well known to the paper coating industry, where it often causes changes in the final structure of the coating layer leading to poor results in terms of gloss, light scattering, surface strength, coverage, uniformity and printability. Such shrinkage has in previous studies been wrongly associated with shrinkage of the polymeric binders used in the coating formulation, by making erroneous comparison with solvent-based paint systems. Natural binders, as starch or proteins, which come from renewable resources and are therefore environmentally friendly, suffer more from this shrinkage phenomenon than synthetic binders. The aim of this research project was to improve the understanding of the processes involved in the drying of a coating layer and to create a model able to describe them. Shrinkage while the coating layer dries has been successfully measured by observing the deflection of coated strips of a synthetic elastically-deformable substrate. Ground calcium carbonate was used as the coating pigment, together with latex binders of both low and high glass transition temperature, Tg, respectively, and also with starch which is a natural film-forming water soluble binder. The final dry coatings were studied with mercury porosimetry and by scanning electron microscopy in order to characterise their porous structure. The flow and rheological properties of the coating colour formulations were measured in order to probe the particle-particle interaction between the different species in the wet coating colour. The void space of the dry coating layers was modelled using Pore-Cor, a software which generates simulated porous networks. A new algorithm was developed to model, within the simulated void space, the effective particles or "skeletal elements" representative of the solid phase of the dried porous system. The water-filled porous structures at the beginning of the shrinkage process (first critical concentration, FCC) were subsequently modelled by creating Pore-Cor structures with the same solid skeletal elements distribution as at the second critical concentration (at which the particles lock their positions), but with higher given porosity to account for the water present The capillary forces acting on the surface of the simulated coating were calculated, and found to be several orders of magnitude larger than the measured shrinkage forces. The shrinkage process was thus described as resulting from the effect of capillary forces in the plane of the coating layer resisted by a stick-slip process, where the capillary forces yield shrinkage only if a resistance force within the drying coating layer holds the structure in place and allows the menisci to form. The stick-slip theory was strongly supported by quantitative comparisons between the experimental forces required to intrude mercury, and the capillary forces within the simulated void structure.Omya AG, Oftringen, Switzerlan

Flood characteristic and fluid rock interactions of a supercritical CO2, brine, rock system: South West Hub, Western Australia

Chemical and/or physical interactions between the storage rock and injected and in-situ created solutes are expected to occur during many underground CO2 storage projects. The intensity of the reactions, however, depends on the abundance of susceptible minerals (e.g. carbonates, clays) in the pore space of the host rock. Such interactions may impact on the multiphase flow characteristics of the underground fluids-rock system over short as well as long time frames. In this research the in-situ multiphase flow characteristics of four sandstone samples have been investigated using a set of laboratory measurements. The samples tested were taken from the Wonnerup Member of the Triassic Lesueur Sandstone which is under consideration as a storage formation in the South-West Hub CO2 geo-sequestration site in Western Australia. All the samples tested show favourable characteristics in terms of storage capacity in the form of residual capillary trapping with residual CO2 saturation varying between 23% and 43%. They underwent a degree of alteration to their petrophysical characteristics which was most significantly pronounced in the case of their absolute gas permeability which showed drops of 25%–60% in the post-flood samples. Formation damage by fines migration is proposed as a mechanism for the observed reduction in permeability. The fines are believed to have originated from the kaolinite particles present in the pore space of the samples

Prediction of petro-physical properties for carbonates

This thesis is concerned with the inversion of lattice pore-network model parameters of carbonate rocks using only the capillary pressure, and then the use of the inverted parameters to predict the water-flooding relative permeabilities of the carbonate rocks. Background: There has been a tendency to claim that pore-network modelling using three-dimensional micro-computed tomography or 3D mathematically created images can predict imbibition relative permeabilities for wettabilities other than strongly water/oil-wetting. This is based on the flexibility for matching data, which is a weakness of pore-network modelling. The method proposed in this thesis is important because a large percentage of the porosity in carbonates is microporosity. Conclusions: We applied stochastic inversion of lattice pore-network model parameters using Hamiltonian Dynamics (Hamiltonian Monte Carlo) to three carbonate rock samples and we predicted water-flooding relative permeabilities with good accuracy by using as constraint only routinely obtained data, such as mercury intrusion capillary pressure (MICP) and oil/water capillary pressure. We found that there is a strong correlation between the amount of microporosity and the volume exponent parameter. This suggests that when microporosity is ignored, the volume exponent will tend to be systematically strongly underestimated. HMC found large variability in wettability that causes mid-sized pores to be invaded at the same level of pressure as larger pores. The coexistence of these events reduces the tendency for preferential flow through large pores, resulting in more uniform flow at the pore scale compared with the case in which flow is restricted only to large pores. Mid-sized pores have an important effect on the connectivity because they could have higher contact angles than larger pores. Therefore, they do not spontaneously imbibe and shield larger pores, improving water-flooding displacement. The wettability of micropores could better explain the gentle curvature of the imbibition water relative permeability compared with the generally assumed mixed-wet large wettability model. The importance of the maximum and minimum observed capillary pressure is directly connected to accounting for the full pore-size distribution. Thus, the common assumption that microporosity can be ignored is unsatisfactory. The ranges of advancing contact angles obtained from the HMC inversion were wider than the ranges of apparent advancing contact angles obtained with analytical determinations in previous studies, and in one case our results were contradictory to the analytical determination. It follows that variability in advancing and receding contact angles is not reflected in the apparent contact angle data outside porous media. Apparent contact angle data outside porous media cannot completely characterise the wettability in porenetwork models because the data does not capture the contact angle variability in porous media. The existence of wetting films depends on the maximum capillary pressure during drainage, and thus wettability alteration during ageing. Our results suggest that matching both connate water at the maximum drainage capillary pressure before ageing and matching residual oil at the minimum imbibition capillary pressure leads to better estimation of the advancing and receding variability in the contact angles

Structural characterisation of porous materials in relation to entrapment of non-wetting fluids

An understanding of the physical mechanisms by which non-wetting fluids become entrapped is important to oil recovery techniques from reservoir rocks, and the structural characterization of porous media. The mechanisms of entrapment and the spatial distribution of non-wetting fluid (mercury) within model materials with similar chemical and geometrical properties to oil reservoir rocks have been investigated using mercury porosimetry and computed X-ray tomography. The combination of both techniques has allowed the direct observation of entrapped mercury within the model materials. In this thesis, a novel experimental technique involving combined mercury porosimetry and mercury thermoporosimetry techniques has been used to determine pore size distributions for disordered porous solids. Mercury porosimetry was conducted, and the mercury entrapped following porosimetry was used as the probe fluid for thermoporosimetry. The fully integrated combination of techniques described here permits the validation of assumptions used in one technique by another. Mercury porosimetry scanning curves were used to establish the correct correspondence between the appropriate Gibbs-Thomson parameter, and the nature of the meniscus geometry in melting, for thermoporosimetry measurements on entrapped mercury. Mercury thermoporosimetry has been used to validate the pore sizes, for a series of sol-gel silica materials, obtained from mercury porosimetry data using the independently-calibrated Kloubek correlations. A Liquid-liquid exchange (LLE) process within mesoporous materials has also been investigated using NMR relaxometry and NMR diffusimetry experiments. In this method, a high affinity liquid (water) displaced a low affinity liquid (cyclohexane) from the sol-gel silica samples. Entrapment of low affinity liquid was observed which was similar to the entrapment of non- wetting fluid observed in mercury porosimetry. In addition, the molecular diffusion of n-pentane has been measured in mesoporous sample using PFG NMR method in a broad temperature range

Incorporation of fault rock properties into production simulation models

This thesis has two aims. First, to investigate the importance of incorporating the multiphase flow properties of faults into production simulation models. Second, to investigate methodologies to incorporate the multiphase flow properties of faults into production simulation models. Tests using simple simulation models suggest that in some situations it is not particularly important to take into account the multiphase flow properties of faults, whereas in other situations the multiphase properties have proved very important. The differences depend on drive mechanism, well position, and the capillary pressure distribution along the fault as well on the parameters that need to be modelled (e. g. bottom-hole pressures, hydrocarbon production rates, water cuts, etc. ). The results show that it is possible for hydrocarbons to flow across a sealing fault (i. e. 100% water saturation) as a result of its threshold pressure being overcome. The relative permeability of fault rocks may be one of the largest unknowns in simulating fluid in structurally complex petroleum reservoirs. Microstructural and petrophysical measurements are conducted on faults from core within the Pierce Field, North Sea. The results are used to calculate transmissibility multipliers (TMs) required to take into account the effect of faults on fluid flow within the Pierce production simulation model. The fault multiphase flow behaviour is approximated by varying the TMs as a function of height above the free water level. This methodology results in an improved history match of production data. Further, the improved model is then used to plan the optimal time to conduct a follow-up 3D seismic survey to identify unswept compartments. Further, an alternative model was proposed to overcome some of the possible limitations that the previous TM treatments may have at certain stages of a reservoir life. The similar behaviour of the different proposed fault models for the Pierce Field indicate that the current faulting system in this model is not largely responsible for the history mismatch in water production. Multiphase flow properties of faults can be incorporated into production simulation models using dynamic pseudofunctions. In this thesis, different dynamic pseudofunctions are generated by conducting high-resolution fluid flow models at the scale of the reservoir simulation grid block, using flow rates similar to those that are likely to be encountered within petroleum reservoirs. In these high-resolution models, both the fault and reservoir rock are given their own capillary pressure and relative permeability curves. The results of the simulations are used to create pseudocurves that are then incorporated into the up-scaled production simulation model to account for the presence of both the fault and undeformed reservoir. Different flow regimes are used to compare the performance of each pseudoisation method with the conventional, single-phase TM fault representations. The results presented in this thesis show that it is more important to incorporate fault multiphase properties in capillary dominated flow regimes than in those that are viscosity dominated. It should, however, be emphasised that the Brooks-Corey relations used to estimate relative permeability and capillary pressure curves of the fault rock in this study have a significant influence on some of these conclusions. In other words, these conclusions may not be valid if the relative permeability curves of fault rocks are very different to those calculated using the aforementioned relationships. Finally, an integrated workflow is outlined showing how dynamic pseudofunctions can be generated in fault juxtaposition models by taking advantage of the dynamic flux preservation feature in Eclipse 10OTM simulator