Initial Saturation Conditions Research Articles

Experimental study on concentrating characteristics during static flash of aqueous NaCl solution at different flash speeds

This experimental study explores the concentration characteristics of aqueous NaCl solution in static flash evaporation, focusing on the equilibrium mass and concentration, at different flash speeds (FS). An aqueous NaCl solution, with an initial concentration (mass fraction) of 0.15 to 0.26, was employed as the working fluid. The superheat varied from 1.49K to 54.9K, while the flash speeds were adjusted from 0.006s-1 to 0.53s-1. The study delineates the flash evaporation process into two regions based on the interplay of heat transfer and steam-carrying effects: one where both factors are co-dominant, and another where heat transfer is the primary controlling element. The results indicate that increasing the flash speed effectively raises the equilibrium concentration in the co-controlled region but has no impact in the region dominated solely by heat transfer. Furthermore, initial saturation conditions at various flash speeds to predict whether the flash evaporation process is occurring in the co-controlled or heat transfer-controlled region are proposed. Calculating method of equilibrium mass/concentration at different flash speeds was set up.

Depressurization induced vapor bubble growth in liquid methane during microgravity

Depressurization and re-pressurization maneuvers are used for cryogenic propellants in spacecraft tanks to mitigate the incoming heat flow and to maintain an appropriate net positive suction head (NPSH). A depressurization maneuver can be used to transfer thermal energy from liquid to vapor and thus allow for subcooling of the liquid by a following, quick pressurization. The depressurization will lead to phase change, caused by the superheat relative to the initial saturation conditions, and the following pressurization will subcool the bulk liquid. Phase change will occur at any of the free surfaces of the bulk liquid or at nucleation sites in cavities at a wall. The mechanism which governs phase change at nucleation sites differs from nucleate boiling due to the temperature distribution in the liquid. In this study, we investigate the behavior of a single nucleation site during a depressurization under microgravity. We observed the bubble growth and evaluated the bubble radius with time. A total of five experiments were performed. The thermodynamic conditions are known and therefore can be correlated to the vapor bubble growth behavior. The superheat in the system varies with time, thus simple models are not applicable but can be used to estimate the bubble size. The data can be used as a reference for further analytical or numerical investigations.

Influence of Convection Term on Temperature Field during Soil Freezing

In recent years, the numerical model of frozen soil has mainly focused on the water-heat equation of unsaturated soil, which is of great significance to predicting engineering stability in frozen soil areas. In these numerical models, the change of freezing temperature is usually ignored, and 0 °C is often used as the freezing condition. In addition, most equations only consider the effect of latent heat released during water freezing on the frozen soil and ignore the effect of high-temperature water on the heat transfer of frozen soil when unfrozen water migrates to the frozen zone. Therefore, there will be deviations under long-time simulation. At the same time, due to excessive attention to the moisture field and neglect of the selection of the temperature field, there is no clear conclusion on when to choose the heat transfer equation with the convection term. The equation in this paper considered the change of freezing temperature under different initial saturation conditions and the convection effect during moisture migration. Through COMSOL 5.5 software simulation, they were combined with the experiment to verify. Three different hydrothermal equations were selected to analyze the effects of latent heat and the effects of convection on the temperature field under different initial saturation conditions. The results show that the convection term plays an essential role in the heat transfer equation for unsaturated soil with high initial saturation. Additionally, the frost heave occurs mainly above the ice front interface. This study provides a reference for when to choose the heat transfer equation with convective terms and can provide help for the construction and prediction of frozen soil in the future.

In Situ Wettability Investigation of Aging of Sandstone Surface in Alkane via X-ray Microtomography

Wettability of surfaces remains of paramount importance for understanding various natural and artificial colloidal and interfacial phenomena at various length and time scales. One of the problems discussed in this work is the wettability alteration of a three-phase system comprising high salinity brine as the aqueous phase, Doddington sandstone as porous rock, and decane as the nonaqueous phase liquid. The study utilizes the technique of in situ contact angle measurements of the several 2D projections of the identified 3D oil phase droplets from the 3D images of the saturated sandstone miniature core plugs obtained by X-ray microcomputed tomography (micro-CT). Earlier works that utilize in situ contact angles measurements were carried out for a single plane. The saturated rock samples were scanned at initial saturation conditions and after aging for 21 days. This study at ambient conditions reveals that it is possible to change the initially intermediate water-wet conditions of the sandstone rock surface to a weakly water wetting state on aging by alkanes using induced polarization at the interface. The study adds to the understanding of initial wettability conditions as well as the oil migration process of the paraffinic oil-bearing sandstone reservoirs. Further, it complements the knowledge of the wettability alteration of the rock surface due to chemisorption, usually done by nonrepresentative technique of silanization of rock surface in experimental investigations.

Effects of Drying and Soil-Base Interface on the Behavior of an Expansive Soil Mixture

Expansive soils exhibit complex behavior associated with significant volume changes triggered by moisture variations induced by changes in environmental conditions. This type of process impacts on soil properties, such as shear strength, stiffness, and permeability. Also, cracks generally develop upon desiccation. There are still several gaps in the current knowledge in this area, particularly in relation to the factors that affect the shear strength of soils and control the formation of drying cracks. This paper focuses on the impact of some of these factors on crack formation and shear strength of an expansive soil mixture made up of 75% kaolin and 25% bentonite, % by mass. Three factors were considered in this research; soil structures (associated with different sample preparation methods), initial saturation, and textures at soil-base interface. Two laboratory series consisting of desiccation plate and soil-base interface shear tests were conducted. For each series, three types of soil specimens were prepared considering different preparation methods (with the associated different soil structures) and initial saturation conditions namely; slurries, fully-saturated compacted and unsaturated compacted specimens. Soil-base interface shear strengths were determined using four different interface textures; grooves oriented perpendicular to shear direction, spiral (circular) indentations, grooves aligned parallel to the shear direction, and smooth surface. For the desiccation plate tests, two types of textures were adopted for the plate-base, namely, circular indentations and smooth to study constrained and free shrinkage conditions, respectively. Results of desiccation tests revealed that cracks developed in the constrained plate (e.g., with circular indentations), whereas no cracks were observed under free displacements conditions (e.g., smooth surface). The direct shear tests revealed that the soil-base interface shear strength is strongly affected by the specimen moisture, soil structure and the direction of the shearing respect to the grooves orientation. For the three set of experiments conducted (i.e., slurry, compacted-saturated, compacted-unsaturated), the highest strength was found for the surface with groove oriented perpendicular to shear direction and the lowest one for the smooth plate. The shear strength associated with the circular-grooves base is in-between those ones observed for the plate with grooves oriented perpendicular and parallel to the shear direction.

History matching of experimental polymer flooding for enhanced viscous oil recovery

Polymer flooding has been widely studied and applied for enhancing reservoir oil recovery. The key to evaluating the potential application of polymer injection is based on a clear understanding of the mechanisms involved in the recovery process. This work focuses on history matching of laboratory core flooding of heavy oil recovery by polymer flooding. We match the experiments through a small-scale simulation model and evaluate the challenges of representing the polymer behavior in porous media. The methodology we propose in this paper aims to model core-flooding experiments with laboratory-measured data. These data come from different experiments, including rheology, single- and two-phase core flooding and are separated into consolidated and uncertain data. Consolidated data include: core volume, permeability, porosity, oil viscosity and density, initial saturation conditions, test temperature and injection rate. The uncertain input parameters involve more complex variables, such as viscosity behavior against shear rate and concentration, residual resistance factor, adsorption, inaccessible pore volume and water–oil relative permeabilities. We compare the simulation output parameters with laboratory results and evaluate the quality of the match for four different two-phase core-flooding experiments. The output parameters include histories for differential pressure, recovery factor, water cut and cumulative produced water, oil and liquid. Our results show that the simulation models successfully matched the experimental data, for all the cases, using appropriate representation of the laboratory parameters. The contribution of this work relies on the proposed methodology, which allows integrating the laboratory data in the construction and validation of core scale simulation models appropriately.

Runoff formation in a small catchment at hillslope and catchment scales

AbstractThe study is focused on runoff formation processes at two scales: the scale of a small mountainous catchment at its outlet and the scale of an experimental plot located in a typical hillslope subregion. The heterogeneous soil profile of the catchments is formed by Cambisols developed on granite bedrocks. The surface runoff appears rarely, the subsurface flow forms a dominant part of the hydrograph. From the period 1998–2008, a set of 44 rainfall–runoff episodes was selected to analyse the rainfall–runoff relationship using multiple regression analysis. From a set of physical parameters, the initial soil water content came out as the statistically significant parameter that controls the runoff forming process at the catchment scale. The rainfall–runoff relationship at the experimental plot scale is more scattered. The dynamic thresholds of rainfall totals apparently control the ratio and the magnitude of stormflow at both scales. Up to the threshold value, the runoff strongly depends on the initial saturation conditions. Above the threshold value, the initial soil moisture conditions are less important. Copyright © 2010 John Wiley & Sons, Ltd.

The Use of Fractional-Flow Theory for Foam Displacement in Presence of Oil

Summary Foam has been extensively used in improved and enhanced oil recovery processes in the petroleum industry over decades. Foam is capable of reducing gas mobility dramatically in porous media, and thus helps keep displacement fronts stable by controlling the mobility ratio between injected gas and reservoir fluids. In this study, models were constructed to investigate the mechanisms of foam displacement in porous media using three-phase fractional-flow theory and ternary diagrams. The strength of foam in the presence of oil was accounted for by using a mobility reduction factor (MRF) for the gas phase that can be routinely measured in laboratory coreflood experiments. The use of MRF is a typical way of describing foam rheology in local steady-state modeling. Results were analyzed in terms of saturation paths in the ternary diagrams, saturation velocities, sweep efficiency and effluent history. Two different initial conditions were selected to demonstrate the importance of initial saturation on the displacement: one with oil phase dominant ((Sw, So) = (0.2, 0.8)) and the other with water phase dominant ((Sw, So) = (0.8, 0.2)). At low MRF (i.e., no foam or weak foam), the efficiency of foam displacement was primarily governed by fast-moving spreading waves that rapidly broke through the porous medium resulting in poor sweep efficiency. An increase in MRF (i.e., stronger foam) altered the nature of the displacement front by making it more piston-like through the development of "shock" fronts and improved sweep efficiency significantly. Once shock fronts dominated the displacement, the importance of initial saturation on the mechanisms of displacement became less pronounced. Calculations also demonstrated that a decrease in oil viscosity made the oil phase more mobile and the formation of shock fronts more prolific, significantly enhancing sweep efficiency. The results in this study imply that if basic fluid properties, injection and initial saturation conditions, and MRF are known, one can reliably predict the mechanisms of foam displacement in porous media even in the presence of oil. The solutions obtained from the three-phase fractional-flow analysis were in good agreement with simulation results in a wide range of MRF values and initial core conditions.

Analysis of Multiphase Flow and Heat Transfer: Pressure Buildup in an Unsaturated Porous Slab Exposed to Hot Gas

This study develops a mathematical model for coupled heat and mass transfer in an unsaturated porous slab exposed to a flowing hot gas. Effects of the initial saturation conditions on associated variables, i.e., total pressure, temperature, moisture content, and multiphase flow, are studied. The Newton-Raphson method based on a finite volume technique is applied. This study emphasizes the influence of initial saturation level and gravitational effect in heat and multiphase flow phenomena associated with this system. Gravity enhances the downward flow of liquid within the porous slab. Pressure buildup occurs near the interface between the wet and the dry zone. However, it appears that the order of magnitude to the total pressure is small. This study explains the fundamental mechanism of multiphase flow that involves heat and mass transfer in a heated unsaturated porous slab.

A Numerical Study of Cirrus Clouds. Part II: Effects of Ambient Temperature, Stability, Radiation, Ice Microphysics, and Microdynamics on Cirrus Evolution

Using the numerical cirrus cloud model developed in Part I of this study, the development of cirrus is examined for four different environmental regimes: warm unstable, cold unstable, warm stable, and cold stable. Despite similar initial saturation conditions, the clouds in the warm and cold cases develop very differently. As summarized below, these four simulations suggest that homogeneous freezing of haze particles and cold temperatures are two major reasons for persistent cirrus clouds. The numerical model is also used here to investigate the roles of several other physical factors in cirrus evolution for a selected environmental regime. These additional factors are radiation, ice crystal habit, latent heat, and ice crystal aggregation. In the warm unstable case, ice particles quickly grow large enough to fall out of the initially supersaturated cloud generation region into the subsaturated lower region. But in the cold unstable case, due to slow growth of cold temperatures, sedimentation is greatly postponed. Thus the cold cirrus tends to persist longer than the warm cirrus. In the unstable cases, diabatic heating tends to slightly destabilize the upper part of the cloud, whose circulation thus is most persistent near the cloud top. The circulation transports water vapor upward to enable long-lasting new ice particle generation. The solar heating tends to be concentrated near the cloud top in both unstable cases, but with quite different IR heating profiles. The IR heating warms the warm cloud near the base and cools it near the top, whereas the cold cloud is radiatively warmed throughout, mostly because it is optically thinner than the warm cloud. In the stable cases, homogeneous nucleation (the homogeneous freezing of haze solution droplets, as parameterized in Part I of this paper) does not occur for the parameterization of heterogeneous nucleation used, leaving the number concentration of ice much smaller than in the unstable cases. However, the individual crystals can grow larger, due to less competition for water vapor, so that they fall out of the initial saturated layer faster than in the unstable cases. The sedimentation rate is slower in the cold stable case than in the warm stable one, again due to slower growth rates at cold temperatures. In neither stable case does the induced diabatic heating destabilize the cloud layer. In this numerical study, it is found that cirrus cloud becomes much less persistent in the simulation without any radiative processes. For warm cirrus, the growth is slightly more vigorous in the daytime than at night, while the opposite is true for cold cirrus. It is found that latent heating plays two opposite roles in the evolution of cirrus. First, it augments the initial perturbation in the growing stage of the cloud, but then tends to stabilize the cloud layer, limiting the development of cirrus at later stages of the cloud evolution. Ice crystal habit has great impact on the evolution of cirrus, especially in an unstable atmosphere. The radiative heating rates are also found to be very sensitive to the type of ice crystal in the cloud. Finally, the role of ice aggregates in the evolution of cirrus is also explored. It is found that the aggregates reduce the volume absorption coefficient, thus decreasing the optical depth and tending to reduce the radiative destabilization.

Determination of Initial Fluid Saturations Using Traced Drilling Media

Abstract Initial saturations of hydrocarbons and water, existing in porous media, control reserves in place and, in many cases, the deliverability/recovery of these reserves. Hence, their accurate determination is essential for proper economic and reservoir engineering evaluation and optimization. Electric logging techniques are commonly used to estimate initial fluid saturations, but may suffer from problems with accurate determination of the log calibration constants for a given reservoir rock, as well as the accurate determination of in situ water resistivity in some situations. Advanced logging techniques, such as magnetic resonance, have been used in recent years to estimate the saturation of bound and free water. The use of these techniques is increasing, but cost and other factors have limited their widespread usage. Various types of reactive tracers and other in situ techniques for the determination of initial fluid saturations have also been used to attempt to determine initial fluid saturations with varying degrees of success. Another family of techniques, on which this paper concentrates, is the actual measurement of in situ initial or swept zone fluid saturations on samples of appropriately obtained, preserved, handled and analysed core material. Different coring techniques and fluid and coring procedures will be discussed, along with the elative merits and advantages/disadvantages of each. Illustration of the results of various techniques will be given with respect to their cost, effectiveness, and accuracy of the data generated. Introduction Initial fluid saturations, defined as the fraction of the interstitial space in a pore system occupied by oil, water, and gas, are key factors in the determination of initial reserves of actual and recoverable hydrocarbons in place and dominate reservoir flow properties due to the strong influence they exhibit on relative permeability (1–5). Surprisingly, in many reservoirs, initial fluid saturations are virtually unknown or improperly measured, resulting in gross over or under estimation of oil or gas reserves in place. The improper determination of these initial saturations may also greatly affect thepotential for formation damage due to phase trapping, resulting in a poor appraisal of deliverability. In some cases, improper initial saturation estimates can lead to the bypassing of potentially productive pay zones, resulting in significant lost reserves or the erroneous completion of ineffective pay and wet or no production from the completed zone. Why Is it Important to Have a Proper Knowledge of Initial Fluid Saturations Improper determination of the initial oil, water or gas saturations existing in porous media may often lead to expensive mistakes in the development of a field. In some cases, large amounts of capital are invested where minimal reserves are present or marginal flow is obtained. In other cases, viable pay is overlooked due to a perceived belief, from improper saturation evaluations, that the pay will be wet or non-productive. The hazards involved with an inadequate understanding of initial saturation conditions can generally be grouped into three categories. Poor Initial Reserves Evaluation Oil or gas in place is based on a simple volumetric calculation of hydrocarbon volume present in the effective porosity of the system.

Suppression of twins in GaAs layers grown on a GaP(111)B substrate by liquid phase epitaxy

Heteroepitaxial growth of GaAs on GaP(111)B was demonstrated by liquid phase epitaxy. In order to suppress the generation of rotational twins, initial saturation conditions of GaAs solution contacting with a GaP substrate were investigated at 800°C. Supersaturated and undersaturated solutions caused a number of twins in the grown GaAs layer, while saturated solution led only a few percents in volume. It was concluded that near equilibrium contact is effective to reduce the twins.

Steam-foam Drive Experiments In One-eighth of a Five-spot Pattern

Abstract Two experiments, Tests SSM01 and SSM02, involving steam-foam drive processes have been performed in 3-D physical models. The physical models which simulated one-eighth of a 2 ha five-spot pattern for a Cold Lake oil sands deposit with a pay zone thickness of approximately 20 m, were designed using a thermal high-pressure scaling approach. Both experiments were carried out successfully with a steam-only injection period followed by steam-foam injection (i.e., steam-surfactant-nitrogen coinjection) periods. The formation of foam in situ was identified by the increase in pressure drop between the injection and the production wells after steam-foam injection. Evidence of the injected steam being diverted from the, steam swept zone into the oil rich zone due to the blocking' effect of foam could be observed in the measured temperature profiles. Enhancement in oil production due to the diversion of steam was observed. In addition, the effect of surfactant injection strategy on the propagation of foam was studied in Test SSM02. It was found that after the foam has been formed, it was more able to propagate away from the injection well by reducing the injected surfactant concentration. Introduction The steam drive process is a proven technique for the recovery of heavy oil and bitumen from underground reservoirs. In an effort to increase the efficiency of this process, considerable emphasis has been placed on developing methods to optimize reservoir conformance, particularly with regard to the problems of steam channeling and gravity override. Foam is well known as a selective blocking agent, and has shown promise for the diversion of steam under conditions of poor reservoir conformance. Steam-foam drive processes are very complex. l-D cores. 3-D physical models and numerical models have been used as too[s to understand the mechanisms of these processes. 3-D physical models can play valuable role in extending the level of understanding from 1-D core size experiments to 3-D geometries and in developing data for validation of numerical models. From an assessment of a 3-D steam-foam drive experiment performed on a large-scale 90 cm physical model by Ridley et al. (l) and the subsequent numerical simulation conducted by law and Ridley(2), it became apparent that many improvements could be made in the design of this unscaled experiment. The most significant problems encountered were:controlling heat losses from the physical model;estimating initial saturations of the test bed which was packed with mined Athabasca oil sands;defining heat loss boundary conditions for numerical simulation: andensuring significant foam effects. The 3-D physical models used in this study were designed by Law and Kimber(3) in a numerical study based on a thermal high-pressure scaling approach. Compared to the earlier unsealed experiment(1), the scaled experiments have:better control over the heat losses from the physical model (i.e., heat losses which are more representative of those in the field); andincreased control over the initial saturation conditions in the physical model.

Model Studies of Pilot Waterfloods

Model Studies of Pilot Waterfloods