Nonisothermal displacement of oil by a solution of an active additive

In earlier work [1, 2] mathematical models have been constructed for processes of displacement of oil from a porous medium by a solution of an active additive, i.e., an additive capable of changing the hydro-dynamic characteristics of the fluid and the medium. An additive of this kind that was considered was a polymer that in the dissolved state influences the properties of the displacing fluid and in the adsorbed state the permeability of the porous medium. Self-similar solutions were obtained corresponding to the problem of frontal displacement from a homogeneous porous medium, and a number of numerical calculations were made. It is natural to generalize this treatment by introducing into the problem a second active factor, which is here taken to be the temperature of the injected fluid. The analysis of the nonisothermal displacement of oil by a solution of an active additive can be transferred without significant modifications to the general problem of displacement of oil by a solution carrying two active agents. The names additive and temperature are retained here only for convenience of exposition.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 90–107, November–December, 1980.We thank A. A. Barmin, A. G. Kulikovskii, and L. A. Chudov for helpful discussions.     

Displacement of oil by a slug of an active additive forced by water through a stratum

The paper gives a solution to the problem of the displacement of oil by a slug for different forms of the sorption isotherm and the distribution function of the additive between the phases and for different values of the initial flooding of the stratum. The process is considered under conditions of reversible sorption and also under conditions of partial retention of the additive by the skeleton of the porous medium. The behavior of slugs in the case of cyclic pumping of a solution of an active additive is investigated.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No, 3, pp. 102–111, May–June, 1982.I thank M. V. Lur'e and M. V. Filinov for suggesting the problem and constant interest in the work, and also V. M. Entov for helpful discussions.     

Displacement of oil by solutions of an active additive from a uniform stratum with allowance for gravity

Self-similar solutions describing the displacement of oil by solutions of an adsorbed active additive have been obtained and investigated [1–3] in the framework of a one-dimensional flow model with neglect of diffusion, capillary, and gravity effects. In the present paper, a self-similar solution is constructed for the problem of oil displacement by an aqueous solution of an active additive from a thin horizontal stratum with allowance for gravity under the assumption that there is instantaneous vertical separation of the phases. This makes it possible to estimate the effectiveness of flooding a stratum by solutions of surfactants and polymers in the cases when gravitational segregation of the phases cannot be ignored.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 87–92, January–February, 1984.     

Structure of the front of oil displacement by a solution of an active additive under nonisothermal conditions when the water saturation of the stratum is high

The structure of the front of oil displacement by a solution of an active additive under nonisothermal conditions in the large-scale approximation without allowance for heat losses has been studied in detail by Braginskaya and Entov [1, 2]. In the present paper, this study is augmented by an analysis of displacement problems when the initial water saturation of the stratum is high. These problems simulate the use of active additives and the pumping of hot water in the lat stage of extraction when an appreciable fraction of the oil has already been displaced from the stratum by ordinary flooding and the initial water saturation of the stratum is high. The exposition is based on the earlier studies [1, 2], whose content is assumed known.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 176–180, January–February, 1982.I thank V. M. Entov for suggesting the problem and helpful discussions.     

Displacement of oil by water from clay bearing strata

The displacement of oil by water from collectors containing clay which swells has been investigated theoretically and experimentally. Swelling of clay due to a change in the ion composition of water filling a stratum can influence the displacement process not only by changing the permeability, as assumed in an earlier paper [1], but also directly by changing the pore space. A modification of the theoretical scheme of the displacement of oil by a solution of an active additive is constructed to take into account these effects; the structure of the displacement front is investigated and the experimental results are analyzed.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 59–65, July–August, 1981.     

Displacement mechanisms of enhanced heavy oil recovery by alkaline flooding in a micromodel

Enhanced oil recovery (EOR) by alkaline flooding for conventional oils has been extensively studied. For heavy oils, investigations are very limited due to the unfavorable mobility ratio between the water and oil phases. In this study, the displacement mechanisms of alkaline flooding for heavy oil EOR are investigated by conducting flood tests in a micromodel. Two different displacement mechanisms are observed for enhancing heavy oil recovery. One is in situ water-in-oil (W/O) emulsion formation and partial wettability alteration. The W/O emulsion formed during the injection of alkaline solution plugs high permeability water channels, and pore walls are altered to become partially oil-wetted, leading to an improvement in sweep efficiency and high tertiary oil recovery. The other mechanism is the formation of an oil-in-water (O/W) emulsion. Heavy oil is dispersed into the water phase by injecting an alkaline solution containing a very dilute surfactant. The oil is then entrained in the water phase and flows out of the model with the water phase.     

Effect of the kinetics of sorption,solution and heat transfer processes on the displacement of oil by active solutions

Among the new methods of enhanced oil recovery the most important are the processes of oil displacement by solutions of active agents (chemical reagents) capable of modifying the hydrodynamic characteristics of the porous flow system. Self-similar processes of oil displacement by active solutions have previously been studied [1–4] for a thermodynamic-equilibrium distribution of the agent in the dissolved in both phases and sorbed states. However, for small-scale displacement processes the effect of the mass transfer kinetics is important. Here the problem of oil displacement by an active solution is solved with allowance for the thermodynamic nonequilibrium of the physicochemical heat and mass transfer processes. In the problem of oil displacement by a solution of water-soluble surfactant or polymer the sorption kinetics of the chemical reagent are taken into account, and in the problem of oil displacement by carbonated water the kinetics of the process of solution of the carbon dioxide in the displaced phase. Allowance for these effects is especially important in interpreting the results of laboratory displacement experiments. The problem of the displacement of oil by hot water is solved with allowance for heat exchange with the surrounding strata. As distinct from the previously investigated case of a stationary temperature distribution in a bounded neighborhood of the formation (supply of heat in accordance with Newton's law) [5, 6], here we analyze the case of nonstationary heating of surrounding rock strata of infinite thickness (Leverrier model).Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 60–71, November–December, 1985.     

Response of the streaks, the active and passive eddies in an unsteady channel flow

Spanwise space–time correlations of the wall shear stress and the longitudinal velocity fluctuations in the low buffer layer of an unsteady channel flow are reported. The imposed amplitude is 20% of the centerline velocity and the imposed frequency covers a large range going from the quasi-steady limit to the bursting frequency of the corresponding steady flow. The unsteady spanwise correlation coefficient is investigated both through its own modulation characteristics (amplitude and phase shifts) and those of the resulting streak spacing. A good correspondence is found between the modulation of the streak spacing and that of the ejection period. The data is further analyzed by temporal filtering of the wall shear stress and streamwise velocity fluctuations. It is shown that the large outer-layer structures play a “passive” role in the unsteady response of the near wall turbulence. The inner wall eddies, in return, are amply responsible for the unsteady reaction of both the turbulent wall shear stress and the streamwise velocity intensities in the buffer layer.     

Vibration and damping analysis of a composite plate with active and passive damping layer

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Displacement of trapped oil from water-wet reservoir rock

Displacement of oil trapped in water-wet reservoirs was analyzed using percolation theory. The critical capillary number of the CDC (Capillary Desaturation Curve) was be predicted based on the pore structure of the medium. The mobilization and stability theories proposed by Stegemeier were used to correlate oil cluster length to the capillary number needed to mobilize the trapped oil. Under the assumption that all pore chambers have the same size, a procedure was developed using the drainage capillary pressure curve and effective accessibility function to predict the CDC curve for a given medium. The prediction of critical capillary numbers was compared with the experimental data from 32 sandstone samples by Chatzis and Morrow. Also, the CDC curve of one sandstone sample was calculated using the procedure developed in this work and compared with the measured data. Very good agreements were obtained.Nomenclature a average radius of a liquid filament [m] - c constant - D pore throat diameter [m] - D _a advancing diameter of an oil cluster [m] - D _af average flowing diameter of the medium [m] - D _da controlling diameter of the medium [m] - D _r receding diameter of an oil cluster [m] - D _X difficulty index - f ratio of length to average radius of an oil cluster - F _i interfacial forces [N] - F _p force from pressure gradient [N] - g wettability function - k absolute permeability [m²] - l length of an oil cluster [m] - l _m mobile oil cluster length [m] - l _s stable oil cluster length [m] - l _w wavelength [m] - n* relative length of an oil cluster - N _c 1 capillary number defined by Equation (1) - N _c 2 capillary number defined by Equation (2) - P _b probability of oil filling a pore - P _c percolation threshold value - p _c capillary pressure [N/m²] - r radius of a pore [m] - r _e average pore radius [m] - S _n the nonwetting phase saturation - S _or residual oil saturation - S _orn normalized oil saturation - v Darcy flow rate [m/s] - X _t total fraction of pores - X _t ^a accessibility - X _e ^a effective accessibility - (D) pore throat size distribution function - _a advancing contact angle - _r receding contact angle - porosity - density of the liquid [kg/m³] - constant in Equation (4) - dynamic length of an oil cluster [m] - interfacial tension [N/m] - viscosity [N/(m s)] - p pressure gradient [N/m³]     

Statistical characteristics of the diffusion of a chemically active additive in a turbulent mixing zone

In the article a numerical solution of the connected system of the equations of turbulent transfer for the fields of the velocity and concentration of a chemically active additive is used to calculate a number of the second moments of the concentration field in a flat mixing zone. The system of transfer equations is derived from the equations for a common function of the distribution of the fields of the pulsations of the velocity and the concentration [1] and is simplified in the approximation of the boundary layer. A closed form of the transfer equations is obtained on the level of three moments, using the hypothesis of four moments [2] and its generalized form for mixed moments of the field of the velocity and the field of a passive scalar. The differential operator of the closed system of the equations of turbulent transfer for the fields of the velocity and the concentration is found by a method of closure not of the parabolic type but of a weakly hyperbolic type [3]. An implicit difference scheme proposed in [4] is used for the numerical solution. The results of the numerical solution are compared with the experimental data of [5].     

Vortex-enhanced mixing through active and passive flow control methods

This study aims to understand the underlying physics of vortex-enhanced mixing through active and passive flow control methods. To find a best flow control method that enhances turbulent mixing through the generation of streamwise vortices, an experimental investigation was carried out to compare active and passive flow control methods of an incompressible axisymmetric jet. For active flow control, the lip of the circular jet was equipped with a single small flap deflected away from the jet stream at an angle of 30° to the jet axis. The flap incorporated a flow control slot through which steady and oscillatory suction were implemented. The active flow control methods require power input to the suction devices. For passive flow control, the lip of the circular jet was equipped with a single small delta tab deflected into the jet stream at an angle of 30° to the jet axis. The chord lengths of the flap and delta tab were one-sixth of the jet diameter. The momentum of jet increased in the case of active flow control by entraining the ambient fluid, whereas momentum decreased in the case of passive flow control. The effect of steady suction saturated for volumetric suction coefficient values greater than 0.82 %. The strength of streamwise vortices generated by the flap were greater than those generated by the delta tab. Steady suction produced positive pressures just downstream of the flow control slot in the central portion of the flap and negative pressures at the flap edges. Oscillatory suction was highly dependent on dimensionless frequency (F ⁺) based on the distance from the flow control slot to the flap trailing edge; the pressures on the central portion of the flap increased for F ⁺ ≤ 0.11 and then decreased for greater F ⁺; finally attained negative pressures at F ⁺ = 0.44. The increase in jet momentum and turbulence intensity, combined with the induced streamwise vorticity, makes steady suction a potential concept for increasing propulsion efficiency through vortex-enhanced mixing. The flow control methods modify the jet flow, which in turn would alter the jet noise spectra.     

Stabilization of a laminar boundary layer by an active surface-localized action

A method for rapidly damping instability waves is proposed as a means of actively controlling a perturbed gas boundary layer flow. The method is based on the use of an active body surface segment which reacts to an instantaneous local pressure variation by producing a proportional local wall displacement normal to the surface with a constant time lag calculated to result in the optimal suppression of unstable disturbances. It is shown that in the one-frequency case the wave number spectrum of the optimal control law contains multiple eigenvalues. The effectiveness of the method is demonstrated over a wide range of variation of the instability wave frequencies and directions. The propagation of an instability wave over an active segment of finite length is calculated using an integral-equation method based on solving the problem of boundary layer flow receptivity to surface vibration. Explicit formulas describing the process of scattering of the instability wave into stable modes at the junction point of the rigid and active surfaces are obtained using the Fourier method and the integral Cauchy theorem.