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Modification of chemical and physical factors in steamflood to increase heavy oil recovery

Description: This report summarizes research progress made during the period October 1, 1988--September 30, 1989. We report advances in the following general areas: (1) chemical-steam simulation model, (2) vapor-liquid flow in porous media, (3) foam flow in porous media, (4) caustic flooding at elevated temperatures, and (5) reservoir heterogeneity. Additional efforts have been devoted in the last quarter of the past year in upgrading and debugging the simulator. New features were added in three-phase relative permeabilities, the vertical equilibrium and the phase behavior subroutines. 123 refs., 79 figs., 2 tabs.
Date: February 1, 1990
Creator: Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

Modification of chemical and physical factors in steamflood in increase heavy oil recovery. Annual report, October 1, 1994--September 30, 1995

Description: The objectives of this contract is to carry our fundamental research in heavy oil recovery in the following areas: displacement and flow properties of fluids involving phase change (condensation-evaporation) in porous media; flow properties of mobility control fluids (such as foam); and the effect of reservoir heterogeneity on oil recovery. The specific projects are motivated by and address the need to improve heavy oil recovery from typical reservoirs as well as less conventional fractured reservoirs. This report covers the work performed in these three areas in the past year. In the area of vapor-liquid flow we present a theoretical and numerical study of steam injection in a pore network. We characterize the displacement in terms of an effective mobility ratio and heat transfer parameters. Displacement patterns axe identified in the parameter space. In another study we discuss the problem of steam injection in fractured systems using visualization with micromodels. The interplay of drainage, imbibition and bubble growth is visualized. Conclusions are reached regarding the potential for steamflooding fractured systems. A third study focuses on the development of a pore-network model for foam formation and propagation in porous media. This model, for the first time, accounts for the fundamental mechanisms of foam propagation at the microscale and leads to the determination of various parameters that are currently treated empirically. The effect of viscous forces in displacements in heterogeneous media is described in two separate studies, one involving an extension of percolation theory to account for viscous effects, and another discussing the effect of geometry in general displacement processes.
Date: October 1996
Creator: Yortsos, Y. C
Partner: UNT Libraries Government Documents Department

Modification of reservoir chemical and physical factors in steamfloods to increase heavy oil recovery. [Quarterly report], January 1--March 31, 1996

Description: Thermal methods, and particularly steam injection, are currently recognized as the most promising for the efficient recovery of heavy oil. Despite significant progress, however, important technical issues remain open. Specifically, still inadequate is our knowledge of the complex interaction between porous media and the various fluids of thermal recovery (steam, water, heavy oil, gases, and chemicals). While, the interplay of heat transfer and fluid flow with pore- and macro-scale heterogeneity is largely unexplored. The objectives of this contract are to continue previous work and to carry out new fundamental studies in the following areas of interest to thermal recovery: displacement and flow properties of fluids involving phase change in porous media; flow properties of mobility control fluids (such as foam); and the effect of reservoir heterogeneity on thermal recovery. During this quarter, we focused on the development of relative permeabilities during steam displacement. Two particular directions were pursued: One involves the derivation of relative permeabilities based on a recently completed work on the pore-level mechanics of steam displacement. Progress has been made to relate the relative permeabilities to effects such as heat transfer and condensation, which are specific to steam injection problems. The second direction involves the development of three-phase relative permeabilities using invasion percolation concepts. We have developed models that predict the specific dependence of the permeabilities of three immiscible phases (e.g. awe, water and gas) on saturations and the saturation history. Both works are still in progress. In addition, work continues in the analysis of the stability of phase change fronts in porous media using a macroscopic approach.
Date: July 1, 1996
Creator: Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

Modification of reservoir chemical and physical factors in steamfloods to increase heavy oil recovery. Quarterly report, October 1--December 31, 1994

Description: Thermal methods, and particularly steam injection, are currently recognized as the most promising for the efficient recovery of heavy oil. Despite significant progress, however, important technical issues remain open. Specifically, still inadequate is our knowledge of the complex interaction between porous media and the various fluids of thermal recovery (steam, water, heavy oil, gases, and chemicals). While, the interplay of heat transfer and fluid flow with pore- and macro-scale heterogeneity is largely unexplored. The objectives of this contract are to continue previous work and to carry out new fundamental studies in the following areas of interest to thermal recovery: displacement and flow properties of fluids involving phase change (condensation-evaporation) in porous media; flow properties of mobility control fluids (such as foam); and the effect of reservoir heterogeneity on thermal recovery. The specific projects are motivated by and address the need to improve heavy oil recovery from typical reservoirs as well as less conventional fractured reservoirs producing from vertical or horizontal wells. This quarterly report covers work accomplished for studies in: vapor-liquid flow; recovery processes in heterogeneous reservoirs; and chemical additives.
Date: December 6, 1994
Creator: Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

Visualization and simulation of immiscible displacement in fractured systems using micromodels: Steam injection

Description: A study of steam and hot water injection processes in micromodel geometries that mimic a matrix-fracture system was undertaken. The followings were observed: Light components existing in the crude oil generated a very high efficient gas-drive at elevated temperatures. This gas generation in conjunction with natural surfactant existing in the crude oil, lead to the formation of a foam in the fracture and to improved displacement in the matrix. We observed that the steam enters the fracture and the matrix depending on whether the steam rate exceeds or not the critical values. The resulting condensed water also moves preferentially into the matrix or the fracture depending on the corresponding capillary number. Since steam is a non-wetting phase as a vapor, but becomes a wetting phase when condensed in a water-wet system, steam injection involves both drainage and imbibition. It was found that all of the oil trapped by the condensed water can be mobilized and recovered when in contact with steam. We also examined hot-water displacement. In comparison with cold-water experiments at the same capillary number, a higher sweep efficiency for both light and heavy oils was observed. It was found that the loam generated in the fracture during hot-water injection, is more stable than in steamflooding. Nonetheless, hot-water injection resulted into less efficient displacement in its absence.
Date: July 1, 1995
Creator: Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

A theoretical analysis of vertical flow equilibrium

Description: The assumption of Vertical Flow Equilibrium (VFE) and of parallel flow conditions, in general, is often applied to the modeling of flow and displacement in natural porous media. However, the methodology for the development of the various models is rather intuitive, and no rigorous method is currently available. In this paper, we develop an asymptotic theory using as parameter the variable R{sub L} = (L/H){radical}(k{sub V})/(k{sub H}). It is rigorously shown that present models represent the leading order term of an asymptotic expansion with respect to 1/R{sub L}{sup 2}. Although this was numerically suspected, it is the first time that is is theoretically proved. Based on the general formulation, a series of models are subsequently obtained. In the absence of strong gravity effects, they generalize previous works by Zapata and Lake (1981), Yokoyama and Lake (1981) and Lake and Hirasaki (1981), on immiscible and miscible displacements. In the limit of gravity-segregated flow, we prove conditions for the fluids to be segregated and derive the Dupuit and Dietz (1953) approximations. Finally, we also discuss effects of capillarity and transverse dispersion.
Date: January 1, 1992
Creator: Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

Percolation models for boiling and bubble growth in porous media

Description: We analyze the liquid-to-vapor phase change in single-component fluids in porous media at low superheats. Conditions typical to steam injection in porous media are taken. We examine nucleation, phase equilibria and their stability, and the growth of vapor bubbles. Effects of pore structure are emphasized. It is shown that at low supersaturations, bubble growth can be described as a percolation process. In the absence of spatial gradients, macroscopic flow properties are calculated in terms of nucleation parameters. A modification of gradient percolation is also proposed in the case of spatial temperature gradients, when solid conduction predominates. 22 refs., 10 figs., 1 tab.
Date: May 1, 1991
Creator: Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

Modification of chemical and physical factors in steamflood to increase heavy oil recovery

Description: Three aspects of vapor-liquid flow in porous media were addressed: (i) Extension of a previous vapor-liquid model for solution gas-drive to a water liquid-water vapor (steam) system in a pore network; (ii) Visualization of steam injection in Hele-Shaw cells and glass micromodels; and (iii) Macroscopic description of concurrent vapor-liquid flow in porous media. Significant progress was made in the study of reservoir heterogeneity and its effects on flow processes. The authors have considered three general areas: (i) The representation of naturally fractured systems; (ii) The large-scale averaging (derivation of pseudo-functions) for displacement in macroscopically heterogeneous systems; and (iii) The study of parallel flow, typically encountered in long and narrow reservoirs. The third area of research in this report involves chemical additives for the improvement of recovery efficiencies. The authors have been studying the following three aspects: (i) Caustic additives at elevated temperatures; (ii) Foam generation; and (iii) Non-Newtonian flow in porous media. The study of caustic injection at elevated temperatures, specifically the silica dissolution and caustic consumption, has been terminated. A technical report will summarize the results obtained. Here, the authors address the remaining aspects (ii) and (iii). 107 refs., 87 figs., 4 tabs.
Date: April 1, 1991
Creator: Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

Modification of chemical and physical factors in steamflood to increase heavy oil recovery

Description: This report covers work performed in the area related to the physicochemical factors for the improvement of the oil recovery efficiency in steamfloods. In this context, three general areas are studied: (1) The understanding of vapor-liquid flow in porous media, whether the flow is internal (boiling), external (steam injection) or countercurrent (as in vertical heat pipes). (2) The effect of reservoir heterogeneity, particularly as it regards fractured systems and long and narrow reservoirs (which are typical of oil reservoirs). (3) The flow properties of additives for the improvement of recovery efficiency, in particular the properties of foams.
Date: April 1, 1992
Creator: Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

Long waves in parallel flow in Hele-Shaw cells

Description: During the past several years the flow of immiscible flow in Hele-Shaw cells and porous media has been investigated extensively. Of particular interest to most studies has been frontal displacement, specifically viscous fingering instabilities and finger growth. The practical ramifications regarding oil recovery, as well as many other industrial processes in porous media, have served as the primary driving force for most of these investigations. By contrast, little attention has been paid to the motion of lateral fluid interface, which are parallel to the main flow direction. Parallel flow is an often encountered, although much overlooked regime. The evolution of fluid interfaces in parallel flow in Hele-Shaw cells is studied both theoretically and experimentally in the large capillary number limit. It is shown that such interfaces support wave motion, the amplitude of which for long waves is governed by the KdV equation. Experiments are conducted in a long Hele-Shaw cell that validate the theory in the symmetric case. 35 refs., 16 figs.
Date: April 1, 1991
Creator: Zeybek, M. & Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

Numerical construction and flow simulation in networks of fractures using fractals

Description: Present models for the representation of naturally fractured systems rely on the double-porosity Warren-Root model or on random arrays of fractures. However, field observation in outcrops has demonstrated the existence of multiple length scales in many naturally fractured media. The existing models fail to capture this important fractal property. In this paper, we use concepts from the theory of fragmentation and from fractal geometry for the numerical construction of networks of fractures that have fractal characteristics. The method is based mainly on the work of Barnsley (1) and allows for great flexibility in the development of patterns. Numerical techniques are developed for the simulation of unsteady single phase flow in such networks. It is found that the pressure transient response of finite fractals behaves according to the analytical predictions of Chang and Yortsos (6), provided that there exists a power law in the mass-radius relationship around the test well location. Otherwise, the finite size effects become significant and interfere severely with the identification of the underlying fractal structure. 21 refs., 13 figs.
Date: November 1, 1991
Creator: Yortsos, Y.C. & Acuna, J.A.
Partner: UNT Libraries Government Documents Department

Modification of reservoir chemical and physical factors in steamfloods to increase heavy oil recovery

Description: Thermal methods, and particularly steam injection, are currently recognized as the most promising for the efficient recovery of heavy oil. Despite significant progress, however, important technical issues remain open. Specifically, still inadequate is our knowledge of the complex interaction between porous media and the various fluids of thermal recovery (steam, water, heavy oil, gases, and chemicals). While, the interplay of heat transfer and fluid flow with pore- and macro-scale heterogeneity is largely unexplored. The objectives of this contract are to continue previous work and to carry out new fundamental studies in the following areas of interest to thermal recovery: displacement and flow properties of fluids involving phase change (condensation-evaporation) in porous media; flow properties of mobility control fluids (such as foam); and the effect of reservoir heterogeneity on thermal recovery. The specific projects are motivated by and address the need to improve heavy oil recovery from typical reservoirs as well as less conventional fractured reservoirs producing from vertical or horizontal wells. During this past quarter, work continued on: the development of relative permeabilities during steam displacement; the optimization of recovery processes in heterogeneous reservoirs by using optical control methods; and in the area of chemical additives, work continued on the behavior of non-Newtonian fluid flow and on foam displacements in porous media.
Date: December 31, 1996
Creator: Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

Modification of reservoir chemical and physical factors in steamfloods to increase heavy oil recovery. [Quarterly report], January 1--March 31, 1997

Description: Thermal methods, and particularly steam injection, are currently recognized as the most promising for the efficient recovery of heavy oil. Despite significant progress, however, important technical issues remain open. Specifically, still inadequate is our knowledge of the complex interaction between porous media and the various fluids of thermal recovery (steam, water, heavy oil, gases, and chemicals). While, the interplay of heat transfer and fluid flow with pore- and macro-scale heterogeneity is largely unexplored. The objectives of this contract are to continue previous work and to carry out new fundamental studies in the following areas of interest to thermal recovery: displacement and flow properties of fluids involving phase change (condensation-evaporation) in porous media; flow properties of mobility control fluids (such as foam); and the effect of reservoir heterogeneity on thermal recovery. The specific projects are motivated by and address the need to improve heavy oil recovery from typical reservoirs as well as less conventional fractured reservoirs producing from vertical or horizontal wells. During this quarter, work continued on the development of relative permeabilities during steam displacement. Most of the work concentrated on the representation of the three-phase flow in terms of a double-drainage process. Work continued on the optimization of recovery processes in heterogeneous reservoirs by using optimal control methods. The effort at present is concentrating in fine-tuning the optimization algorithm as well as in developing control methodologies with different constraints. In parallel, we continued experiments in a Hele-Shaw cell with two controlled injection wells and one production well. In the area of chemical additives work continued on the behavior of non-Newtonian fluid flow and on foam displacements in porous media.
Date: August 1, 1997
Creator: Yortsos, Y. C.
Partner: UNT Libraries Government Documents Department

A Pore-Network Model of In-Situ Combustion in Porous Media

Description: This report the use of dual pore networks (pores and solid sites) for modeling the effect of the microstructure on combustion processes in porous media is considered. The model accounts for flow and transport of the gas phase in the porespace, where convection predominates, and for heat transfer by conduction in the solid phase. Gas phase flow in the pore and throats is governed by Darcy's law.
Date: January 29, 2001
Creator: Lu, Chuan & Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

Investigation of Multiscale and Multiphase Flow, Transport and Reaction in Heavy Oil Recovery Processes

Description: This report is an investigation of various multi-phase and multiscale transport and reaction processes associated with heavy oil recovery. The thrust areas of the project include the following: Internal drives, vapor-liquid flows, combustion and reaction processes, fluid displacements and the effect of instabilities and heterogeneities and the flow of fluids with yield stress. These find respective applications in foamy oils, the evolution of dissolved gas, internal steam drives, the mechanics of concurrent and countercurrent vapor-liquid flows, associated with thermal methods and steam injection, such as SAGD, the in-situ combustion, the upscaling of displacements in heterogeneous media and the flow of foams, Bingham plastics and heavy oils in porous media and the development of wormholes during cold production.
Date: May 29, 2001
Creator: Yortsos, Y. C.
Partner: UNT Libraries Government Documents Department

Identification of the Permeability Field of Porous Medium from the Injection of Passive Tracer

Description: In this paper, a method was proposed which focused on the question, namely on how to invert data on arrival times at various (and numerous) points in the porous medium to map the permeability field. The method, elements of which were briefly described in (9), is based on a direct inversion of the data, as will be described below , rather than on the optimization of initial random (or partly constrained) guesses of the permeability field, to match the available data, as typically done in the analogous problem of pressure transients. The direct inversion is based on two conditions, that Darcy's law for single-phase flow in porous media is valid, and that dispersion of the concentration of the injected tracer is negligible. While the former is a well-accepted premise, the latter depends on injection and field conditions, and may not necessarily apply in all cases. Based on these conditions, we formulate a nonlinear boundary value problem, the coefficients of which depend on the experimental arrival time data.
Date: October 18, 1999
Creator: Zhan, Lang & Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

Visualization and simulation of immiscible displacement in fractured systems using micromodels: Imbibition

Description: A study of imbibition processes in micromodel geometries that mimic a matrix-fracture system was undertaken. Experiments in glass micromodels and pore network simulation were conducted. It was observed that, at low capillary number values the wetting fluid preferentially invaded the matrix. Two critical capillary numbers were identified, one for the start of penetration in the fracture when the viscosity ratio was much less than one, and another for which the rate of propagation of the front in the fracture is the same with that in the matrix, when the viscosity ratio was greater than one. These critical capillary numbers were well matched with the results of a pore network simulation. We also developed a simplified theory for both critical numbers. Free imbibition in fractured system was investigated an(] compared favorably with pore network simulation. This process first involves the ra.pi(i invasion of the matrix, followed by the subsequent penetration of the fracture.
Date: July 1, 1995
Creator: Hadghighi, M. & Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

A study of steady-state steam-water counterflow in porous media

Description: Vapor-liquid counterflow in porous media arises in processes such as heat pipes, oil recovery and geothermal systems. Previous studies analysed these phenomena in separate contexts. This paper presents a unified description from which previous models result as limiting cases. The analysis includes capillarity, heat conduction, and Kelvin effects. The importance of each term to various processes is examined. Significantly, it is found that the critical heat flux is not constant but increases with decreasing permeability. A threshold permeability is identified below which steady states may not exist. Analogous conclusions are reached regarding liquid-dominated geothermal systems. 24 refs., 15 figs.
Date: February 1, 1990
Creator: Satik, C.; Parlar, M. & Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

Fractal analysis of pressure transients in the Geysers Geothermal Field

Description: The conventionally accepted models for the interpretation of pressure transient tests in naturally fractured reservoirs usually involve simplistic assumptions regarding the geometry and transport properties of the fractured medium. Many single well tests in this type of reservoirs fail to show the predicted behavior for dual or triple porosity or permeability systems and cannot be explained by these models. This paper describes the application of a new model based on a fractal interpretation of the fractured medium. The approach, discussed elsewhere [2], [6], is applied to field data from The Geysers Geothermal Field. The objective is to present an alternative interpretation to well tests that characterizes the fractured medium in a manner more consistent with other field evidence. The novel insight gained from fractal geometry allows the identification of important characteristics of the fracture structure that feeds a particular well. Some simple models are also presented that match the field transient results.
Date: January 1, 1992
Creator: Acuna, J.A.; Ershaghi, I. & Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

Visualization experiments on steam injection in Hele-Shaw cells

Description: Flow visualization experiments have been successfully employed in reservoir engineering research for many years. They involve 2-D geometries in transparent Hele-Shaw cells and glass micromodels. Although much work has been done on immiscible flows (drainage or imbibition), visualization of steamfloods, which constitute a major part of current EOR methods, has not been attempted to data. In this paper, we present experimental results on steam injection in a transparent, pyrex glass Hele-Shaw cell. Both synthetic (Dutrex 739) and natural heavy oils were used under a variety of conditions, including effects of gravity.
Date: March 1, 1992
Creator: Kong, Xianli; Haghighi, M. & Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

On the Upscaling of Reaction-Transport Processes in Porous Media with Fast Kinetics

Description: This report is organized as follows: Provide a brief review of the upscaling constraints of the type (2) for a typical diffusion-reaction system. In this an analogy with two-phase flow in porous media was drawn. Then, using the methodology of QW a problem at the unit cell for the computation of the effective mass transfer coefficient, in processes where local thermodynamic equilibrium applies was derived. This problem is found to be different than in QW, as it depends on the gradients of the macroscale variable, and can be cast in terms of an eigenvalue problem. Two simple, examples, one involving advection-dissolution and another involving drying in a pore network, was presented to illustrate the coupling between scales and to show the quantitative effect in case this coupling was neglected. Finally, similar ideas and an illustrative example was applied to reaction-diffusion systems with fast kinetics, where an equilibrium state is approached.
Date: January 9, 2001
Creator: Kechagi, P.; Tsimpanogiannis, I.; Yortsos, Y. C. & Lichtner, P.
Partner: UNT Libraries Government Documents Department

Effects of capillary heterogeneity on vapor-liquid counterflow in porous media

Description: Based on a continuum description, the effect of capillary heterogeneity, induced by variation in permeability, on the steady state, countercurrent, vapor-liquid flow in porous media is analyzed. It is shown that the heterogeneity acts as a body force, that may enhance or diminish gravity effects on heat pipes. Selection rules that determine the steady states reached in homogeneous, gravity-driven heat pipes are also formulated. It is shown that the infinite'' two-phase zone may terminate by a substantial change in the permeability somewhere in the medium. The two possible sequences, liquid - liquid dominated - dry, or liquid - vapor dominated - dry find applications in geothermal systems. Finally, it is shown that although weak heterogeneity affects only gravity controlled flows, stronger variations in permeability can give rise to significant capillary effects.
Date: June 1, 1992
Creator: Stubos, A.K.; Satik, C. & Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department