Simulation Studies Of Water Research Articles

Simulation study of water and gas injection process into the Azadegan reservoir for enhanced oil recovery

AbstractIt is necessary to improve oil production from reservoirs. Various methods have been proposed to increase oil extraction from reservoir. Each method has specific challenges. In this research, the effect of water and gas injection in to Azadegan reservoir has been analyzed. Azadegan oil field is located south of Iran. In this study, water, immiscible gas and water alternating gas injected to reservoir and its effect on enhanced oil recovery have been investigated. Finally, a comparison between results of methods is provided. Results show that effective method for enhanced oil recovery is immiscible gas injection with 46% oil production efficiency and water alternating gas injection with 36% oil production efficiency. This study shows that oil production efficiency can be increased if duration of gas injection is increased. This study shows, increasing viscosity of water in water alternating gas scenario did not improve the production of Azadegan reservoir.

The local compressibility of liquids near non-adsorbing substrates: a useful measure of solvophobicity and hydrophobicity?

We investigate the suitability of the local compressibility χ(z) as a measure of the solvophobicity or hydrophobicity of a substrate. Defining the local compressibility as the derivative of the local one-body density ρ(z) w.r.t. the chemical potential μ at fixed temperature T, we use density functional theory (DFT) to calculate χ(z) for a model fluid, close to bulk liquid–gas coexistence, at various planar substrates. These range from a ‘neutral’ substrate with a contact angle of θ≈90°, which favours neither the liquid nor the gas phase, to a very solvophobic, purely repulsive substrate which exhibits complete drying, i.e. θ = 180°. We find that the maximum in the local compressibility χ(z), which occurs within one–two molecular diameters of the substrate, and the integrated quantity χex (the surface excess compressibility, defined below) both increase rapidly as θ increases and the substrate becomes more solvophobic. χ(z) provides a more pronounced indicator of solvophobicity than the density depletion in the vicinity of the surface which increases only weakly with increasing θ. For the limiting case of drying, θ = 180°, we find lnχ(l) ∼ l, where l is the thickness of the intruding film of gas which diverges in the approach to bulk coexistence μ → μco. When the fluid is confined in a parallel slit with two identical solvophobic walls, or with competing solvophobic and solvophilic walls, χ(z) close to the solvophobic wall is altered little from that at the single substrate. We connect our results with simulation studies of water near to hydrophobic surfaces exploring the relationship between χ(z) and fluctuations in the local density and between χex and the mean-square fluctuation in the number of adsorbed molecules.

Water in Nanopores: III. Surface Phase Transitions of Water on Hydrophilic Surfaces

Water in hydrophilic pores shows a rich phase diagram due to the appearance of the surface phase transitions. By simulation studies of water in various hydrophilic pores, we have analyzed the evolution of the water phase diagram with the strengthening of a water−wall interaction potential U0. A second-order wetting transition is observed rather close to the liquid−vapor critical temperature when U0 ≈ −2 kcal/mol. The wetting temperature rapidly decreases with the strengthening of a water−wall interaction. A first-order wetting transition, accompanied by a prewetting transition, is observed when the hydrophilicity of the walls is within the range of −4 ≤ U0 ≤ −3 kcal/mol. At U0 ≤ −4 kcal/mol, the temperature of the wetting transition is below the bulk freezing temperature, and one or two layering transitions appear instead of the prewetting transition. Coexistence curves of the first layering transition are well described by the two-dimensional Ising model with critical exponent β = 0.125. The critical tem...

Computer simulation study of water using a fluctuating charge model

Hydrogen bonding in small water clusters is studied through computer simulation methods using a sophisticated, empirical model of interaction developed by Ricket al (S W Rick, S J Stuart and B J Berne 1994J. Chem. Phys. 101 6141) and others. The model allows for the charges on the interacting sites to fluctuate as a function of time, depending on their local environment. The charge flow is driven by the difference in the electronegativity of the atoms within the water molecule, thus effectively mimicking the effects of polarization of the charge density. The potential model is thus transferable across all phases of water. Using this model, we have obtained the minimum energy structures of water clusters up to a size often. The cluster structures agree well with experimental data. In addition, we are able to distinctly identify the hydrogens that form hydrogen bonds based on their charges alone, a feature that is not possible in simulations using fixed charge models. We have also studied the structure of liquid water at ambient conditions using this fluctuating charge model.