Multi–Front Phase Transitions During Nonisothermal Filtration of Live Paraffin–Base Crude

By numerical modeling of nonisothermal filtration of multicomponent oil with allowance for the Joule—Thomson effect, adiabatic effect, and heat of phase transitions that occur during oil degassing and paraffin crystallization, the formation of profiles of phase–saturation, concentrations of oil components, and temperature in oil beds is studied. It is shown that consideration of many components results in occurrence of phase–transition fronts during degassing of oil components and paraffin crystallization. In turn, paraffin crystallization gives rise to temperature oscillations. Depending on the initial paraffin concentration and on the ratio of phase–transition heats for oil degassing and paraffin crystallization in an oil bed, either decaying or steady–state temperature oscillations are observed.     

Application of potential theory to a problem of the limiting configuration of the stagnant zones in the displacement of viscoplastic oil by water

A solution of the problem of determining the limiting-equilibrium portions of residual viscoplastic oil in connection with the displacement of oil by water from a porous formation in a multiwell system is constructed by the methods of potential theory and analyzed. The results of a comparison with a standard exact solution are presented for certain asymptotic cases.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 182–185, January–February, 1989.     

Mathematical simulation of micellar-polymer displacement of oil from flooded strata

The micellar-polymer method of increasing the oil recovery from strata [1] is currently regarded as promising. The method consists of injecting into an oil stratum, which has previously undergone ordinary flooding, a relatively small amount, a slug, of micellar solution (5–10% of of the pore volume), which is propelled through the stratum by slugs of a highly viscous buffer fluid (aqueous solution of a polymer). In turn, the system of slugs is propelled from the injection points to the extraction wells by the water used for ordinary flooding. The displacement of the oil that remains after flooding in the stratum is achieved by a decrease in the coefficient of surface tension at the boundaries of the micellar solution with the oil and the water to the value 10^–2-10^–3 dyn/cm, which leads to a decrease in the amount of fixed oil and also to a control of the mobility of the fluids, which is achieved by varying the concentrations of the components of the micellar solution and the buffer fluid. The main components of micellar solutions are: a hydrocarbon fluid (oil or its fractions), water, surface-active substances. The relationships between the main components, and also the addition of salts and alcohol to the water component have a strong influence on the interaction between the solution and the stratal oil and water [2]. The micellar solution considered in the present paper dissolves oil but does not mix with water; the relationships between the components in it are characteristic of the solutions used to increase oil recovery from strata.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 84–93, November–December, 1982.     

Numerical modeling of the process of oil displacement from reservoirs with zonal nonuniformity

In extracting oil from nonuniform reservoirs a considerable fraction remains unrecovered from the zones of lesser permeability. The mechanism of displacement of oil from reservoirs with zonal nonuniformity is investigated within the framework of the two-dimensional Muskat-Meres model of combined oil, water and gas flow [1]. A wholly conservative difference scheme implicit in the saturations and pressure is used for the calculations. Various reservoir exploitation regimes are considered with the object of seeking means of improving the characteristics of the process.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 177–180, September–October, 1987.     

Unsteady displacement of an oil deposit in a flow of stratal water

Unsteady problems concerning the displacement of gas and oil deposits in a seepage flow of stratal water are of specific interest to oil and gas hydrogeology, and in the planning and analysis of the processes of reservoir exploitation. Firstly, a change of the hydrogeological environment in a region of already formed deposits involves their displacement. Secondly, when one of two adjacent deposits is developed, a displacement of the other occurs in the artificial flow of stratal water which is produced. Papers [1–3] investigate the steady configuration of gas—water or water—oil contacts in the presence of a seepage flow of stratal water under the deposit. The unsteady problem considered below is a generalization of the problem in paper [3]. Its characteristic property is the presence of mobile boundaries separating the regions with flow of different fluids in the horizontal plane.Translated from Izvestiya Akademii Nauk SSSR, Mekh. Zhidk. Gaza, No. 2, pp. 177–179, March–April, 1985.     

Numerical investigation of the process of displacement of oil by steam

A calculation model of the process of displacement of oil by steam, based on the equations of three-phase nonisothermal flow with allowance for phase transitions in the water-steam system, is proposed. This model is used for the numerical investigation of the recovery of oil from wateroil zones by means of steam injection. The extraction of oil from wateroil zones is one of the difficult problems of the theory of exploitation of petroleum deposits. The presence of two zones with sharply different fluid resistances leads to considerable nonuniformity in production rates. It is shown that injecting steam significantly reduces this nonuniformity.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 78–84, July–August, 1987.     

Comparative analysis of methods of areal flooding of stratified reservoirs of anomalous oil

When anomalous oils in productive reservoirs are displaced by water [1], residual undisplaced oil remains [2, 3]. For calculating the volume of the unrecovered oil, most studies have been of homogeneous reservoirs [4–8]. In the present paper, the residual volume is assessed using an inhomogeneous-stratified-model. The inhomogeneity of the strata is described by the random distributions of Weibull or Pearson (gamma-distribution), which are characteristic of oilfields possessing anomalous properties (see, for example, [9]). A parametric study is made of four known schemes of areal flooding: two-point (straight line), five-, seven-, and nine-point [10]. The obtained estimates of the volume of the residual oil can be used for rational selection of the parameters for exploiting anomalous oilfields.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 121–126, May–June, 1985.     

On the mechanism of cyclic flooding for oil extraction

A two-dimensional model is considered for the displacement of oil by water from a stratum that is nonuniform over its thickness when a periodic elastic flow regime is employed.Translated from Izvestiya Akademii Nauk SSSR, Meknanika Zhidkosti i Gaza, No. 3, pp. 58–66, May–June, 1980.     

Simulation of the thermal recovery process in a layered reservoir

The thermohydrodynamic interaction of the layers in a layered oil reservoir in the presence on in situ combustion is considered.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.3, pp. 122–128, May–June, 1994.     

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.     

Mathematical simulation of biogenic processes in oil strata

An attempt is made to construct a mathematical model of the development of bacteria in an oil stratum and investigate on the basis of this model the main features of the process.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 84–91, October–December, 1981.     

Horizontal displacement of miscible fluids from fractured porous media

The equations of horizontal displacement of miscible fluids from thin fractured porous formations are derived with allowance for all three mechanisms of mass transfer between the blocks and the fractures. The effect of the difference in the densities of oil and gas and the displacement velocity on oil production is analyzed.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.3, pp. 87–95, May–June, 1992.The author is grateful to A. K. Kurbanov for useful discussions and his intererst in the work and also to G. D. Istomin for carrying out the numerical calculations.     

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.     

Matrix–Fracture Transfer through Countercurrent Imbibition in Presence of Fracture Fluid Flow

Although a lot of research has been done in modeling the oil recovery from fractured reservoirs by countercurrent imbibition, less attention has been paid to the effect of the fracture fluid velocity upon the rate of oil recovery. Experiments are conducted to determine the effect of fracture flow rate upon countercurrent imbibition. A droplet detachment model is proposed to derive the effective water saturation in a thin boundary layer at the matrix–fracture interface. This effective boundary water saturation is a function of fluid properties, fluid velocity in the fracture and fracture width. For a highly water–wet porous medium, this model predicts an increase in the boundary water saturation with increase in fracture fluid velocity. The increase in boundary water saturation, in turn, increases the oil recovery rate from the matrix, which is consistent with the experimental results. The model also predicts that the oil recovery rate does not vary linearly with the boundary water saturation.     

A Parametric Model for Predicting Relative Permeability-Saturation-Capillary Pressure Relationships of Oil–Water Systems in Porous Media with Mixed Wettability

A parametric two-phase, oil–water relative permeability/capillary pressure model for petroleum engineering and environmental applications is developed for porous media in which the smaller pores are strongly water-wet and the larger pores tend to be intermediate- or oil-wet. A saturation index, which can vary from 0 to 1, is used to distinguish those pores that are strongly water-wet from those that have intermediate- or oil-wet characteristics. The capillary pressure submodel is capable of describing main-drainage and hysteretic saturation-path saturations for positive and negative oil–water capillary pressures. At high oil–water capillary pressures, an asymptote is approached as the water saturation approaches the residual water saturation. At low oil–water capillary pressures (i.e. negative), another asymptote is approached as the oil saturation approaches the residual oil saturation. Hysteresis in capillary pressure relations, including water entrapment, is modeled. Relative permeabilities are predicted using parameters that describe main-drainage capillary pressure relations and accounting for how water and oil are distributed throughout the pore spaces of a porous medium with mixed wettability. The capillary pressure submodel is tested against published experimental data, and an example of how to use the relative permeability/capillary pressure model for a hypothetical saturation-path scenario involving several imbibition and drainage paths is given. Features of the model are also explained. Results suggest that the proposed model is capable of predicting relative permeability/capillary pressure characteristics of porous media mixed wettability.     

Hydrodynamical modeling of the development of non-homogeneous oil reservoirs

Results of mathematical modeling of two-phase flow in non-homogeneous (layered) reservoirs are reported. Characteristic patterns of flow in reservoirs with high layer permeability contrast are investigated. It is shown that in such reservoirs crossflow between layers must be taken into account. Specific features of the use of hydrodynamic methods of improving oil recovery in such reservoirs based upon flow pattern control are studied. The possibility of using rational flow management to improve oil recovery partially blocking the reservoir in the neighborhood of the wells is demonstrated.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 87–94, November–December, 1995.     

Experimental investigation of countercurrent capillary imbibition (CCI) in natural rock samples at various temperatures

CCI in natural oil-saturated core samples has been experimentally investigated. The oil displacement coefficient is determined by comparing the initial and final oil saturations of the sample. The effect of temperature and time on the intensity and rate of CCI is explored. The results of the investigation are scaled up to correspond to the conditions of a real oil deposit on the basis of a well-known similarity criterion. It is shown that the rate of CCI falls significantly with increase in the size of the blocks. In order to intensify CCI it is necessary to heat most of the reservoir with a high-temperature heat transfer agent.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 62–67, May–June, 1990.     

Nonisothermal displacement of high-paraffin oils by water with allowance for solid-phase precipitation

A mathematical model of the nonisothermal displacement of oil by water with allowance for solid-phase precipitation is proposed. Self-similar solutions of the problem of nonisothermal displacement of oil from a homogeneous, thermally insulated formation are obtained. The inverse problems of determining the relative phase permeabilities and the temperature dependence of the paraffin saturation concentration from laboratory displacement data are solved. Exact solutions of the non-self-similar problems of the displacement of high-paraffin oil by a slug of hot water and of the thermal delay problem are obtained. The nonisothermal displacement of high-paraffin oils by water with allowance for heat transfer to the surrounding strata is subjected to qualitative analysis.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 126–137, May–June, 1989.The authors are grateful to A. K. Kurbanov and Yu. V. Kapyrin for useful discussions and their interest in the work.     

Barothermal effect in the displacement of oil from a porous medium

The formation of the temperature field due to the barothermal effect when oil is displaced from a porous medium by water is investigated in the piston displacement and two-phase flow approximations. The approach of the displacement front to the outlet from the porous medium leads to a sharp increase in temperature and the temperature anomalies are observed to depend on the saturation.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.3, pp. 104–109, May–June, 1992.     

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.