An experimental investigation of retention of liquids in corners of a square capillary

The retention of liquids in the corners of a 0.03-cm square capillary after the passage of a gas slug was studied experimentally as a function of capillary number in the range from 10(-3) to 10(-6). In gas-wetting liquid systems, for capillary number greater than 5 x 10(-4), the retention of a wetting liquid in the corners showed a strong dependence on the capillary number; i.e., the retention of the liquid decreased with decreasing capillary number. For capillary number less than 10(-4), the retention of a wetting liquid was found to be determined by the capillary forces and the rate (or viscous) effect was negligible. In gas-oil-water systems involving double displacements--gas was displacing oil which was in turn displacing water--the total retention of water and oil vs capillary number curve showed the same trend as the retention of a wetting phase in a gas-wetting liquid system. However, because of the viscous effect, the water retention showed a continuous decrease with decreasing capillary number and could be lower than the capillary equilibrium value at very low capillary numbers. As a result of this, the oil retention vs capillary number curve in the double displacement process showed a minimum; i.e., oil retention increased with decreasing capillary number in the range of very low capillary numbers.     

The Effect of Reservoir Wettability on the Production Characteristics of the VAPEX Process: An Experimental Study

The impact of fractional wettability on the production characteristics of a VAPEX process at the macroscale was investigated. Conventional VAPEX experiments were conducted in a 220 Darcy random packing of glass beads in a rectangular physical model and n-pentane was used to recover the Cold Lake bitumen from the oil-saturated model in the absence of connate water. The composition of oil-wet beads in the packed bed was altered from completely water-wet beads to completely oil-wet beads at different proportions of oil-wet beads mixed with water-wet beads. A substantial increase (about 40%) in the production rate of live oil was observed during the VAPEX process when the wettability of the porous packing was entirely oil-wet beads. A critical oil-wet fraction of 0.66 was found for the heterogeneous packing of water-wet and oil-wet beads of similar size distribution. Above this critical composition, the live oil production rate was not affected by further increase in the proportion of the oil-wet beads. It is believed that above this critical composition of the oil-wet beads, the crevice flow process is dominated by the continuity of higher conductivity live oil films between particles through the oil-wet regions. Below this critical composition, the live oil production rate increased linearly with the fraction of the oil-wet beads in the packing. The oil-wet regions favor the live oil drainage compared to that of the water-wet regions as they enhance the rate of imbibition of the live oil from the oil-filled pores to the vacated pores near the nominal VAPEX interface. These two factors enhance the live oil production rate during the VAPEX process. The solvent content of the live oil, the solvent-to-oil ratio (SOR), and the residual oil saturation did not correlate strongly with the proportion of the oil-wet beads in the packing. The average solvent content of the live oil and the residual oil saturation were measured to be 48% by weight and 7% by volume respectively.     

Modeling of adsorption dynamics at air-liquid interfaces using statistical rate theory (SRT)

A large number of natural and technological processes involve mass transfer at interfaces. Interfacial properties, e.g., adsorption, play a key role in such applications as wetting, foaming, coating, and stabilizing of liquid films. The mechanistic understanding of surface adsorption often assumes molecular diffusion in the bulk liquid and subsequent adsorption at the interface. Diffusion is well described by Fick's law, while adsorption kinetics is less understood and is commonly described using Langmuir-type empirical equations. In this study, a general theoretical model for adsorption kinetics/dynamics at the air-liquid interface is developed; in particular, a new kinetic equation based on the statistical rate theory (SRT) is derived. Similar to many reported kinetic equations, the new kinetic equation also involves a number of parameters, but all these parameters are theoretically obtainable. In the present model, the adsorption dynamics is governed by three dimensionless numbers: psi (ratio of adsorption thickness to diffusion length), lambda (ratio of square of the adsorption thickness to the ratio of adsorption to desorption rate constant), and Nk (ratio of the adsorption rate constant to the product of diffusion coefficient and bulk concentration). Numerical simulations for surface adsorption using the proposed model are carried out and verified. The difference in surface adsorption between the general and the diffusion controlled model is estimated and presented graphically as contours of deviation. Three different regions of adsorption dynamics are identified: diffusion controlled (deviation less than 10%), mixed diffusion and transfer controlled (deviation in the range of 10-90%), and transfer controlled (deviation more than 90%). These three different modes predominantly depend on the value of Nk. The corresponding ranges of Nk for the studied values of psi (10(-2)相似文献   

Studies of dynamic surface tension of polyoxyethylene alkylphenols at the air–water interface

This paper presents the study of dynamic surface tension of polyoxyethylene alkylphenol surfactants (Igepals) at the air–solution interface. The experimental investigation of the surface tension dynamics are carried out using a pendant drop method for two of the representative alkylphenols (Igepal-630 and Igepal-720) nonionic surfactants. The general trend of the dynamic surface tension for the two surfactants appears to be similar. However, the absolute surface activities are different. Between the two poloxyethylene alkylphenol surfactants, it was found that Igepal-C0-630 has a higher surface activity and a lower critical micelle concentration (CMC) value. This agreed well with their reported hydrophile–lipophile balance (HLB). The equilibrium adsorption parameters for these surfactant systems have been estimation using two different methods and are in good agreement. The theoretical model developed for the surface tension dynamics based on the Statistical Rate Theory (SRT) in our earlier (J. Colloid Interface Sci., 286, 2005, 14–27) work satisfactorily predicted the experimental results for the present systems.     

On the Geometry and Topology of 3D Stochastic Porous Media

The nature of geometric and topological information contained in statistical correlation functions was investigated systematically using simulated porous media, generated by the level-cut of Gaussian random fields. Pore space partitioning techniques based on multiorientation scanning were implemented to determine the pore and neck size distributions, coordination number distribution, and genus of a number of model porous media. These results were correlated with the statistical properties (porosity and correlation function) of the microstructure, revealing for the first time the extent of morphological diversity of a broad class of stochastically reconstructed porous media. It was found that the dominant factor explaining microstructural variability among the media studied is the dimensionless length of spatial correlation. Accordingly, the resolution at which the void space is discretized during simulation was shown to affect significantly the resulting pore and neck size distributions and specific genus. It was also found that the average coordination number of simulated porous media is independent of correlation length, but decreases slightly with decreasing porosity. Copyright 2000 Academic Press.     

Bubble Migration Velocity in a Uniform Pore Network

Transport in Porous Media - Gas bubbles can be generated naturally or introduced artificially in porous media. Gas bubble migration through porous media governs the rate of gas emission to the...     

Modeling of the 3D rocking problem

The rocking motion of a rigid rectangular prism on a moving base is a complex three dimensional phenomenon. Although, with very few exceptions, the previous models in the literature make the simplified assumption that this motion is planar, this is usually not true since a body will probably not be aligned with the direction of the ground motion. Thus, even in the case where the body is fully symmetric, the rocking motion involves three dimensional rotations and displacements.In this work, a three dimensional formulation is introduced for the rocking motion of a rigid rectangular prism on a deformable base. Two models are developed: the Concentrated Springs Model and the Winkler Model. Both sliding and uplift are taken into account and the fully non-linear equations of the problem are developed and solved numerically.The models developed are later used to examine the behavior of bodies subjected to general ground excitations. The contribution of phenomena neglected in previous models, such as twist, is stressed.     

Simulation of capillary pressure curves using bond correlated site percolation on a simple cubic network

A stochastic approach to network modelling has been used to simulate quasi-static immiscible displacement in porous media. Both number-based and volume-based network saturation results were obtained. Number-based results include: number-based saturation curves for primary drainage, secondary imbibition and secondary drainage, fluid distribution data, and cluster trapping history. Using pore structure data of porous media, it is possible to convert the number-based curves to capillary pressure — saturation relationships. Pore size distribution functions and pore shapes which are thought to closely represent Berea sandstone samples were used to predict the capillary curves. The physical basis of these calculations is a one-to-one correspondence between the cumulative node and bond index fractions in the network analysis, and the cumulative number-based distributions of pore body and pore throat diameters, respectively. The oil-water capillary pressure curve simulated for primary drainage closely resembles those measured experimentally. The agreement between the simulated and the measured secondary imbition and secondary drainage curves is less satisfactory.     

A computerized technique for measuringin-situ concentrations during miscible displacements in porous media

A technique for measurement of thein-situ concentration in an unconsolidated porous medium has been developed. The method involves measurement of electrical conductivityin-situ, under dynamic conditions, for flow involving brine of differing concentrations, at selected locations along the porous medium and relating it to the brine strength. Data acquisition and analysis is carried out using a Hewlett — Packard micro-computer and its interface. A user-friendly software was designed and developed for the system. The measurement technique was evaluated by studying the effect of brine concentration, brine flow rate, and by conducting miscible displacements experiment. The experimentally measured dispersion coefficients for the porous medium agreed closely with the value predicted by the correlation available in the literature.     

Electrical Conductivity and Percolation Aspects of Statistically Homogeneous Porous Media

A method of 3-D stochastic reconstruction of porous media based on statistical information extracted from 2-D sections is evaluated with reference to the steady transport of electric current. Model microstructures conforming to measured and simulated pore space autocorrelation functions are generated and the formation factor is systematically determined by random walk simulation as a function of porosity and correlation length. Computed formation factors are found to depend on correlation length only for small values of this parameter. This finding is explained by considering the general percolation behavior of a statistically homogeneous system. For porosities lower than about 0.2, the dependence of formation factor on porosity shows marked deviations from Archie's law. This behavior results from the relatively high pore space percolation threshold (0.09) of the simulated media and suggests a limitation to the applicability of the method to low porosity media. It is additionally demonstrated that the distribution of secondary porosity at a larger scale can be simulated using stochastic methods. Computations of the formation factor are performed for model media with a matrix-vuggy structure as a function of the amount and spatial distribution of vuggy porosity and matrix conductivity. These results are shown to be consistent with limited available experimental data for carbonate rocks.