Publications of year 1998

Conference articles

H. J. Bertin, O. G. Apaydin, L. M. Castanier, and A. R. Kovscek. Foam Flow in Heterogeneous Porous Media: Effect of Crossflow. In , Tulsa, OK, USA, April 1998.
[pdf]
Keywords: Foam, Crossflow, Experimental Work.

Abstract

Previous studies of foam generation and transport were conducted, mainly, in one-dimensional and homogeneous porous media. However, the field situation is primarily heterogeneous and multidimensional. To begin to bridge this gap, we have studied foam formation and propagation in an annularly heterogeneous porous medium. The experimental system was constructed by centering a 5.0 cm diameter cylindrical Fontainebleau sandstone core inside an 8.9 cm acrylic tube and packing clean Ottawa sand in the annular region. The sandstone permeability is roughly 0.1 d while the unconsolidated sand permeability is about 7 d. Experiments with and without crossflow between the two porous media were conducted. To prevent crossflow, the cylindrical face of the sandstone was encased in a heat-shrink Teflon sleeve and the annular region packed with sand as before. Nitrogen is the gas phase and an alpha olefin sulfonate (AOS 1416) in brine is the foamer. The aqueous phase saturation distribution is garnered using X-ray computed tomography. Results from this study are striking. When the heterogeneous layers are in capillary communication and cross flow is allowed, foam fronts move at identical rates in each porous medium as quantified by the CT-scan images. Desaturation by foam is efficient and typically complete in about 1 PV of gas injection. When cross flow is prohibited, foam partially plugs the high permeability sand and diverts flow into the low permeability sandstone. The foam front moves through the low permeability region faster than in the high permeability region.

BibTex Entry:

@CONFERENCE{SPE39678,
TITLE ={Foam Flow in Heterogeneous Porous Media: Effect of Crossflow},
AUTHOR ={H. J. Bertin and O. G. Apaydin and L. M. Castanier and A. R. Kovscek},
year ={1998},
month =apr,
JOURNAL={SPE/DOE Improved Oil Recovery Symposium},
address ={Tulsa, OK, USA},
KEYWORDS ={Foam, Crossflow, Experimental Work},
URL ={http://ekofisk.stanford.edu/supria/publications/public/tr118.pdf},
ABSTRACT ={Previous studies of foam generation and transport were conducted, mainly, in one-dimensional and homogeneous porous media. However, the field situation is primarily heterogeneous and multidimensional. To begin to bridge this gap, we have studied foam formation and propagation in an annularly heterogeneous porous medium. The experimental system was constructed by centering a 5.0 cm diameter cylindrical Fontainebleau sandstone core inside an 8.9 cm acrylic tube and packing clean Ottawa sand in the annular region. The sandstone permeability is roughly 0.1 d while the unconsolidated sand permeability is about 7 d. Experiments with and without crossflow between the two porous media were conducted. To prevent crossflow, the cylindrical face of the sandstone was encased in a heat-shrink Teflon sleeve and the annular region packed with sand as before. Nitrogen is the gas phase and an alpha olefin sulfonate (AOS 1416) in brine is the foamer. The aqueous phase saturation distribution is garnered using X-ray computed tomography. Results from this study are striking. When the heterogeneous layers are in capillary communication and cross flow is allowed, foam fronts move at identical rates in each porous medium as quantified by the CT-scan images. Desaturation by foam is efficient and typically complete in about 1 PV of gas injection. When cross flow is prohibited, foam partially plugs the high permeability sand and diverts flow into the low permeability sandstone. The foam front moves through the low permeability region faster than in the high permeability region.},

}

E. R. German, S. Akin, and L. M. Castanier. Experimental and Theoretical Investigation of Multiphase Flow in Fractured Media. In , San Diego, California, USA, September 1998.
[pdf]
Keywords: Fractures, Imbibition, Experimental Work, Analytical Model, Relative Permeability.

Abstract

A laboratory flow apparatus was built to obtain data on water-air displacements in horizontal single-fractured block systems. For this purpose, two configurations have been used: a two matrixblock system with a 1mm spacer between the blocks, and a two matrix-block system with no spacer. During the experiments, porosity and saturation calculations along the cores have been made utilizing an X-ray Computerized Tomography (CT) scanner. Saturation images were reconstructed in 3-D to observe better matrix-fracture interactions. Differences in fluid saturations and relative permeabilities caused by changes in fracture width have also been analyzed. The fracture system without a spacer showed a more stable front and faster breakthrough than the other. However, the final water saturation was higher in the wide fracture system, thus showing that capillary pressure in the narrow fracture has more effect on recovery. Simulations of the experiments were made using a commercial reservoir simulator (Eclipse). Fracture relative permeability and capillary pressure curves were obtained by history matching the experiments. Sensitivity analysis of parameters such as fracture relative permeability, capillary pressure in the fracture, and fracture width were also conducted. The results showed that the assumption of fracture relative permeability equal to phase saturation is incorrect. Moreover, larger flow resistance in the fractures was observed by comparing the experiments with numerical simulation work . We found that the processes are both capillary and viscous dominated.

BibTex Entry:

@CONFERENCE{ERGerman,
TITLE ={Experimental and Theoretical Investigation of Multiphase Flow in Fractured Media},
AUTHOR ={E. R. German and S. Akin and L. M. Castanier},
JOURNAL={Geothermal Resources Council Meeting 1998 Annual Meeting},
year ={1998},
month =sep,
address ={San Diego, California, USA},
KEYWORDS ={Fractures, Imbibition, Experimental Work, Analytical Model, Relative Permeability},
URL ={http://ekofisk.stanford.edu/supria/publications/public/grc98.pdf},
ABSTRACT ={A laboratory flow apparatus was built to obtain data on water-air displacements in horizontal single-fractured block systems. For this purpose, two configurations have been used: a two matrixblock system with a 1mm spacer between the blocks, and a two matrix-block system with no spacer. During the experiments, porosity and saturation calculations along the cores have been made utilizing an X-ray Computerized Tomography (CT) scanner. Saturation images were reconstructed in 3-D to observe better matrix-fracture interactions. Differences in fluid saturations and relative permeabilities caused by changes in fracture width have also been analyzed. The fracture system without a spacer showed a more stable front and faster breakthrough than the other. However, the final water saturation was higher in the wide fracture system, thus showing that capillary pressure in the narrow fracture has more effect on recovery. Simulations of the experiments were made using a commercial reservoir simulator (Eclipse). Fracture relative permeability and capillary pressure curves were obtained by history matching the experiments. Sensitivity analysis of parameters such as fracture relative permeability, capillary pressure in the fracture, and fracture width were also conducted. The results showed that the assumption of fracture relative permeability equal to phase saturation is incorrect. Moreover, larger flow resistance in the fractures was observed by comparing the experiments with numerical simulation work . We found that the processes are both capillary and viscous dominated.},

}

A. R. Kovscek. Reservoir Simulation of Foam Displacement Processes. In , Beijing, China, October 1998.
[pdf]
Keywords: Heavy Oil, Steam, Thermal Recovery.

Abstract

Steam injection has had a profound impact on the production of heavy crude oil. Steam, however, is inviscid compared to a viscous oil and is not the ideal displacement agent. Field studies and laboratory tests have shown that foaming the steam phase through the aid of a suitable surfactant in aqueous solution can achieve mobility control of injected gases and mitigate the effects of gravity override. Thus, production is improved. Unfortunately, simulation models and simulation tools that accurately gauge the effects of foam on gas mobility in porous media are not readily available. Recent advances in modeling gas mobility in the presence of foam are reviewed. These include the socalled bubble population balance method, scaling arguments to obtain representative foam texture and hence gas mobility, and semi-empirical alteration of gas mobility. The bubble population balance is then illustrated by means of a few sample calculations.

BibTex Entry:

@CONFERENCE{unitar,
TITLE ={Reservoir Simulation of Foam Displacement Processes},
AUTHOR ={A. R. Kovscek},
JOURNAL={7th Unitar International Conference on Heavy Crude and Tar Sands},
year ={1998},
month =oct,
address ={Beijing, China},
KEYWORDS ={Heavy Oil, Steam, Thermal Recovery},
URL ={http://ekofisk.stanford.edu/supria/publications/public/tr118.pdf},
ABSTRACT ={Steam injection has had a profound impact on the production of heavy crude oil. Steam, however, is inviscid compared to a viscous oil and is not the ideal displacement agent. Field studies and laboratory tests have shown that foaming the steam phase through the aid of a suitable surfactant in aqueous solution can achieve mobility control of injected gases and mitigate the effects of gravity override. Thus, production is improved. Unfortunately, simulation models and simulation tools that accurately gauge the effects of foam on gas mobility in porous media are not readily available. Recent advances in modeling gas mobility in the presence of foam are reviewed. These include the socalled bubble population balance method, scaling arguments to obtain representative foam texture and hence gas mobility, and semi-empirical alteration of gas mobility. The bubble population balance is then illustrated by means of a few sample calculations.},

}

J.M. Schembre, S. Akin, L. M. Castanier, and A. R. Kovscek. Spontaneous Water Imbibtion in Diatomite. In , Bakersfield, CA, USA, May 1998.
[pdf]
Keywords: Experimental Work, Diatomites, Capillary Pressure.

Abstract

A systematic experimental investigation of capillary pressure characteristics and fluid flow in diatomite has been accomplished. Using an X-ray CT scanner and a specially constructed imbibition cell, we study spontaneous water imbibition processes in diatomite and for reference Berea sandstone and chalk. The mass of water imbibed as a function of time is also measured. Imbibition is restricted to cocurrent flow. Despite a marked difference in rock properties including permeability and porosity, we find similar trends in saturation profiles and weight gain versus time functions. Imbibition in diatomite is relatively rapid when initial water saturation is low due to large capillary forces.

BibTex Entry:

@CONFERENCE{SPE46211,
TITLE ={Spontaneous Water Imbibtion in Diatomite},
AUTHOR ={J.M. Schembre and S. Akin and L. M. Castanier and A. R. Kovscek},
JOURNAL={SPE Western Regional Meeting},
year ={1998},
month =may,
address ={Bakersfield, CA, USA},
KEYWORDS ={Experimental Work, Diatomites, Capillary Pressure},
URL ={http://ekofisk.stanford.edu/supria/publications/public/spe46211.pdf},
ABSTRACT ={A systematic experimental investigation of capillary pressure characteristics and fluid flow in diatomite has been accomplished. Using an X-ray CT scanner and a specially constructed imbibition cell, we study spontaneous water imbibition processes in diatomite and for reference Berea sandstone and chalk. The mass of water imbibed as a function of time is also measured. Imbibition is restricted to cocurrent flow. Despite a marked difference in rock properties including permeability and porosity, we find similar trends in saturation profiles and weight gain versus time functions. Imbibition in diatomite is relatively rapid when initial water saturation is low due to large capillary forces.},

}

Y. Wang, A. R. Kovscek, and W. E. Brigham. Effect of Mobility Ratio on Areal Sweep Efficiency and Pattern Flood Behavior. In , Carmel, CA, USA, October 1998.
[pdf]
Keywords: Mobility Control, Sweep Efficiency, Simulation.

Abstract

It is well known, for unit mobility ratio, that the areal sweep efficiency of a staggered-linedrive pattern is always better than a five-spot pattern. However, this observation does not hold for very favorable mobility ratios. We present simulation results and, with the help of streamline and saturation distributions, explain the differences between unit and favorable mobility ratios. Simulations compare well with experiments conducted elsewhere. Accurate definition of breakthrough time is also discussed for multiphase, streamline, simulation results. The exact definition of breakthrough is difficult due to physical dispersion in experiments and numerical dispersion in simulations.

BibTex Entry:

@CONFERENCE{Wang_1998,
TITLE ={Effect of Mobility Ratio on Areal Sweep Efficiency and Pattern Flood Behavior},
AUTHOR ={Y. Wang and A. R. Kovscek and W. E. Brigham},
JOURNAL={19th Annual International Energy Agency Workshop and Symposium},
year ={1998},
month =oct,
address ={Carmel, CA, USA},
KEYWORDS ={Mobility Control, Sweep Efficiency, Simulation},
URL ={http://ekofisk.stanford.edu/supria/publications/public/iea98A2.pdf},
ABSTRACT ={It is well known, for unit mobility ratio, that the areal sweep efficiency of a staggered-linedrive pattern is always better than a five-spot pattern. However, this observation does not hold for very favorable mobility ratios. We present simulation results and, with the help of streamline and saturation distributions, explain the differences between unit and favorable mobility ratios. Simulations compare well with experiments conducted elsewhere. Accurate definition of breakthrough time is also discussed for multiphase, streamline, simulation results. The exact definition of breakthrough is difficult due to physical dispersion in experiments and numerical dispersion in simulations.},

}

Internal reports

O. G. Apaydin, H. J. Bertin, L. M. Castanier, and A. R. Kovscek. An Experimental Investigation of Foam Flow in Homogeneous and Heterogeneous Porous Media. Technical report, Stanford University, CA, USA, June 1998.
[pdf]
Keywords: Foam, Experimental Work, Mobility Control.

Abstract

Foam is used to reduce the high mobility of gas-drive fluids and improve the contact between oil and these injected fluids. We require a better understanding of the effect of surfactant concentration on foam flow in porous media. Besides this, the literature on foam flow and transport in heterogeneous systems is sparse although the field situation is primarily heterogeneous and multidimensional. In this study, foam flow experiments were conducted first in homogenous sand packs to investigate the effect of surfactant concentration on foam flow and then a heterogeneous experimental setup was prepared to observe heterogeneity and multidimensional flow effects on foam propagation. The homogeneous core experiments were conducted in a cylindrical aluminum core holder that was packed with a uniform Ottawa sand. Sand permeability is about 7.0 Darcy. The experiments were interpreted in terms of evolution of in-situ water saturation as a function of time by the usage of CT scanner, cumulative water recovery, and pressure drop across the core. At very low surfactant concentration, no significant benefit was observed. But when stable foam generation started sweep efficiency (water recovery), breakthrough time, and pressure drop increased as surfactant concentration increased. At the next stage, a Fontainebleau sandstone was centered inside an acrylic tube and the annular region was packed with clean Ottawa sand to construct a heterogeneous porous medium. The permeability contrast between sandstone and sand was 67 to 1. Experiments with and without crossflow between the two porous media were conducted. To prevent crossflow, a heat-shrink Teflon jacket was placed on the cylindrical face of sandstone. In-situ water saturation distribution was garnered using the CT scanner. The results from this study are striking. When the heterogeneous layers were in capillary communication and cross flow was allowed, foam fronts move at identical rates in each porous medium as quantified by the CT-scan images. Desaturation by foam was efficient and typically complete in about 1 PV of gas injection. When cross flow was prohibited, foam partially plugs the high permeability sand and diverted flow into the low permeability sandstone. The foam front moved through the low permeability region faster than in the high permeability region.

BibTex Entry:

@TECHREPORT{TR112,
TITLE ={An Experimental Investigation of Foam Flow in Homogeneous and Heterogeneous Porous Media},
AUTHOR ={O. G. Apaydin and H. J. Bertin and L. M. Castanier and A. R. Kovscek},
YEAR ={1998},
MONTH =jun,
INSTITUTION = {Stanford University, CA, USA},
KEYWORDS ={Foam, Experimental Work, Mobility Control},
URL ={http://ekofisk.stanford.edu/supria/publications/public/tr112.pdf},
ABSTRACT ={Foam is used to reduce the high mobility of gas-drive fluids and improve the contact between oil and these injected fluids. We require a better understanding of the effect of surfactant concentration on foam flow in porous media. Besides this, the literature on foam flow and transport in heterogeneous systems is sparse although the field situation is primarily heterogeneous and multidimensional. In this study, foam flow experiments were conducted first in homogenous sand packs to investigate the effect of surfactant concentration on foam flow and then a heterogeneous experimental setup was prepared to observe heterogeneity and multidimensional flow effects on foam propagation. The homogeneous core experiments were conducted in a cylindrical aluminum core holder that was packed with a uniform Ottawa sand. Sand permeability is about 7.0 Darcy. The experiments were interpreted in terms of evolution of in-situ water saturation as a function of time by the usage of CT scanner, cumulative water recovery, and pressure drop across the core. At very low surfactant concentration, no significant benefit was observed. But when stable foam generation started sweep efficiency (water recovery), breakthrough time, and pressure drop increased as surfactant concentration increased. At the next stage, a Fontainebleau sandstone was centered inside an acrylic tube and the annular region was packed with clean Ottawa sand to construct a heterogeneous porous medium. The permeability contrast between sandstone and sand was 67 to 1. Experiments with and without crossflow between the two porous media were conducted. To prevent crossflow, a heat-shrink Teflon jacket was placed on the cylindrical face of sandstone. In-situ water saturation distribution was garnered using the CT scanner. The results from this study are striking. When the heterogeneous layers were in capillary communication and cross flow was allowed, foam fronts move at identical rates in each porous medium as quantified by the CT-scan images. Desaturation by foam was efficient and typically complete in about 1 PV of gas injection. When cross flow was prohibited, foam partially plugs the high permeability sand and diverted flow into the low permeability sandstone. The foam front moved through the low permeability region faster than in the high permeability region.},

}

S. K. Bhat and A. R. Kovscek. Modeling Permeability Alteration in Diatomite Reservoirs During Steam Drive. Technical report, Stanford University, CA, USA, July 1998.
[pdf]
Keywords: Diatomites, Thermal Recovery, Steam, Network Modeling.

Abstract

There is an estimated 10 billion barrels of original oil in place (OOIP) in diatomaceous reservoirs in Kern County, California. These reservoirs have low permeability ranging from 0.1 to 10 mD. Injection pressure controlled steam drive has been found to be an efficient way to recover oil from these reservoirs. However, steam drive in these reservoirs has its own complications. The rock matrix is primarily silica (SiO2). It is a known fact that silica is soluble in hot water and its solubility varies with temperature and pH. Due to this fact, the rock matrix in diatomite may dissolve into the aqueous phase as the temperature at a location increases or it may precipitate from the aqueous phase onto the rock grains as the temperature decreases. Thus, during steam drive silica redistribution will occur in the reservoir along with oil recovery. This silica redistribution causes the permeability and porosity of the reservoir to change. Understanding and quantifying these silica redistribution effects on the reservoir permeability might prove to be a key aspect of designing a steam drive project in these formations. In this study the first aspect that we examine is the relative importance of the factors that govern the transfer of silica between the rock matrix and the aqueous phase. On the basis of analytical solutions for simple one-dimensional systems and the conditions that typically exist in diatomite reservoirs, we conclude that the silica concentration in the aqueous phase is the equilibrium silica solubility corresponding to the temperature of that location. This is likely true for the whole length of the reservoir, except near injectors and producers. We call this attainment of “local chemical equilibrium”. This implies for a given location, that when we know the temperature variation, we can predict the amount of silica transfer between rock grains and the aqueous phase surrounding it. From a qualitative argument we know that the extent of permeability alteration will depend on the pore-level characteristics of this rock apart from the extent of silica redistribution. We tried to infer the pore-level shapes and distributions of pore-sizes of this rock by a variety of experimental methods including mercury intrusion / retraction porosimetery, scanning electron microscopy, core-level permeability measurements and X-ray computed tomography (CT scanning). On basis of these investigations we inferred the shape of pore-body and pore-throat size distributions for an outcrop sample of diatomite. These were unimodel distributions with a high positive skew. The average pore-throat size was around 6 mm and the average pore-body size was around 40 mm. In the final phase of this study, we found mathematical relations that are useful to predict the permeability alteration with amount of silica transfer between the rock matrix and the aqueous phase given the pore-level information of diatomite. This was done using pore-network models. To start, we correlated the pore dimensions with properties like permeability and porosity. Next, we modeled the deposition / dissolution processes in terms of changing pore dimensions and then used these altered pore dimensions to find the altered permeability and porosity. This way, we were able to quantify the effect of silica redistribution on permeability of the reservoir.

BibTex Entry:

@TECHREPORT{TR113,
TITLE ={Modeling Permeability Alteration in Diatomite Reservoirs During Steam Drive},
AUTHOR ={S. K. Bhat and A. R. Kovscek},
YEAR ={1998},
MONTH =jul,
INSTITUTION = {Stanford University, CA, USA},
KEYWORDS ={Diatomites, Thermal Recovery, Steam, Network Modeling},
URL ={http://ekofisk.stanford.edu/supria/publications/public/tr113.pdf},
ABSTRACT ={There is an estimated 10 billion barrels of original oil in place (OOIP) in diatomaceous reservoirs in Kern County, California. These reservoirs have low permeability ranging from 0.1 to 10 mD. Injection pressure controlled steam drive has been found to be an efficient way to recover oil from these reservoirs. However, steam drive in these reservoirs has its own complications. The rock matrix is primarily silica (SiO2). It is a known fact that silica is soluble in hot water and its solubility varies with temperature and pH. Due to this fact, the rock matrix in diatomite may dissolve into the aqueous phase as the temperature at a location increases or it may precipitate from the aqueous phase onto the rock grains as the temperature decreases. Thus, during steam drive silica redistribution will occur in the reservoir along with oil recovery. This silica redistribution causes the permeability and porosity of the reservoir to change. Understanding and quantifying these silica redistribution effects on the reservoir permeability might prove to be a key aspect of designing a steam drive project in these formations. In this study the first aspect that we examine is the relative importance of the factors that govern the transfer of silica between the rock matrix and the aqueous phase. On the basis of analytical solutions for simple one-dimensional systems and the conditions that typically exist in diatomite reservoirs, we conclude that the silica concentration in the aqueous phase is the equilibrium silica solubility corresponding to the temperature of that location. This is likely true for the whole length of the reservoir, except near injectors and producers. We call this attainment of “local chemical equilibrium”. This implies for a given location, that when we know the temperature variation, we can predict the amount of silica transfer between rock grains and the aqueous phase surrounding it. From a qualitative argument we know that the extent of permeability alteration will depend on the pore-level characteristics of this rock apart from the extent of silica redistribution. We tried to infer the pore-level shapes and distributions of pore-sizes of this rock by a variety of experimental methods including mercury intrusion / retraction porosimetery, scanning electron microscopy, core-level permeability measurements and X-ray computed tomography (CT scanning). On basis of these investigations we inferred the shape of pore-body and pore-throat size distributions for an outcrop sample of diatomite. These were unimodel distributions with a high positive skew. The average pore-throat size was around 6 mm and the average pore-body size was around 40 mm. In the final phase of this study, we found mathematical relations that are useful to predict the permeability alteration with amount of silica transfer between the rock matrix and the aqueous phase given the pore-level information of diatomite. This was done using pore-network models. To start, we correlated the pore dimensions with properties like permeability and porosity. Next, we modeled the deposition / dissolution processes in terms of changing pore dimensions and then used these altered pore dimensions to find the altered permeability and porosity. This way, we were able to quantify the effect of silica redistribution on permeability of the reservoir.},

}

W. E. Brigham, A. R. Kovscek, and L. M. Castanier. SUPRI Heavy Oil Research Program Twenty First Annual Report. Technical report, Stanford University, CA, USA, 1998.
[pdf]
Keywords: Reservoir Definition, In-Situ Combustion, Heavy Oil, Steam, EOR, Formation Evaluation.

Abstract

Supri-A yearly research report.

BibTex Entry:

@TECHREPORT{TR111,
TITLE ={SUPRI Heavy Oil Research Program Twenty First Annual Report},
AUTHOR ={W. E. Brigham and A. R. Kovscek and L. M. Castanier},
YEAR ={1998},
INSTITUTION ={Stanford University, CA, USA},
KEYWORDS ={Reservoir Definition, In-Situ Combustion,Heavy Oil,Steam, EOR,Formation Evaluation},
URL ={http://ekofisk.stanford.edu/supria/publications/public/tr111.pdf},
ABSTRACT ={Supri-A yearly research report.},

}

G. L. Messner. A Comparison of Mass Rate and Steam Quality Reductions to Optimize Steamflood Performance.. Technical report, Stanford University, CA, USA, July 1998.
[pdf]
Keywords: Thermal Recovery, Steam, Heavy Oil.

Abstract

Many operators of steamdrive projects will reduce the heat injection rate as the project matures. The major benefit of this practice is to reduce the fuel costs and thus extend the economic life of the project. However, there is little industry consensus on whether the heat cuts should take the form of; (1) mass rate reductions while maintaining the same high steam quality, or (2) steam quality decreases while keeping the same mass rate. Through the use of a commercial three-phase, three-dimensional simulator, the oil recovery schedules obtained when reducing the injected steam mass rate or quality with time were compared under a variety of reservoir and operating conditions. The simulator input was validated for Kern River Field conditions by using the guidelines developed by Johnson, et al. (1989) for four steamflood projects in Kern River. The results indicate that for equivalent heat injection rates, decreasing the steam injection mass rate at a constant high quality will yield more economic oil than reducing the steam quality at a constant mass rate. This conclusion is confirmed by a sensitivity analysis which demonstrates the importance of the gravity drainage/steam zone expansion mechanism in a low-pressure, heavy oil steamflood with gravity segregation. Furthermore, the impact of discontinuous silts and nonuniform initial temperatures within the steamflood zone was studied, indicating again that a decreasing mass rate injection strategy is a superior operating practice.

BibTex Entry:

@TECHREPORT{TR108,
TITLE ={A Comparison of Mass Rate and Steam Quality Reductions to Optimize Steamflood Performance.},
AUTHOR ={G. L. Messner},
YEAR ={1998},
MONTH =jul,
INSTITUTION = {Stanford University, CA, USA},
KEYWORDS ={Thermal Recovery, Steam, Heavy Oil},
URL ={http://ekofisk.stanford.edu/supria/publications/public/tr108.pdf},
ABSTRACT ={Many operators of steamdrive projects will reduce the heat injection rate as the project matures. The major benefit of this practice is to reduce the fuel costs and thus extend the economic life of the project. However, there is little industry consensus on whether the heat cuts should take the form of; (1) mass rate reductions while maintaining the same high steam quality, or (2) steam quality decreases while keeping the same mass rate. Through the use of a commercial three-phase, three-dimensional simulator, the oil recovery schedules obtained when reducing the injected steam mass rate or quality with time were compared under a variety of reservoir and operating conditions. The simulator input was validated for Kern River Field conditions by using the guidelines developed by Johnson, et al. (1989) for four steamflood projects in Kern River. The results indicate that for equivalent heat injection rates, decreasing the steam injection mass rate at a constant high quality will yield more economic oil than reducing the steam quality at a constant mass rate. This conclusion is confirmed by a sensitivity analysis which demonstrates the importance of the gravity drainage/steam zone expansion mechanism in a low-pressure, heavy oil steamflood with gravity segregation. Furthermore, the impact of discontinuous silts and nonuniform initial temperatures within the steamflood zone was studied, indicating again that a decreasing mass rate injection strategy is a superior operating practice.},

}

J. M. Schembre, S. Akin, and A. R. Kovscek. Spontaneous Imbibition in Low Permeability Porous Media. Technical report, Stanford University, CA, USA, December 1998.
[pdf]
Keywords: Imbibition, Experimental Work, Simulation, Relative Permeability, Capillary Pressure.

Abstract

A systematic experimental investigation of capillary pressure characteristics and fluid flow in diatomite was begun. Using an X-ray CT scanner and a specially constructed imbibition cell, we study spontaneous water imbibition processes in diatomite and, for reference, Berea sandstone and chalk. The mass of water imbibed as a function of time is also measured. Imbibition is restricted to cocurrent flow. Despite a marked difference in rock properties such as permeability and porosity, we find similar trends in saturation profiles and weight gain versus time functions. Imbibition in diatomite is relatively rapid when initial water saturation is low due to large capillary forces. Using a non-linear regression analysis together with the experimental data, the capillary pressure and water relative permeability curves are determined for the diatomite in the water-air system. The results given for displacement profiles by numerical simulation match the experimental results.

BibTex Entry:

@TECHREPORT{TR114,
TITLE ={Spontaneous Imbibition in Low Permeability Porous Media},
AUTHOR ={J. M. Schembre and S. Akin and A. R. Kovscek},
YEAR ={1998},
MONTH =dec,
INSTITUTION ={Stanford University, CA, USA},
KEYWORDS ={Imbibition, Experimental Work, Simulation, Relative Permeability, Capillary Pressure},
URL ={http://ekofisk.stanford.edu/supria/publications/public/tr114.pdf},
ABSTRACT ={A systematic experimental investigation of capillary pressure characteristics and fluid flow in diatomite was begun. Using an X-ray CT scanner and a specially constructed imbibition cell, we study spontaneous water imbibition processes in diatomite and, for reference, Berea sandstone and chalk. The mass of water imbibed as a function of time is also measured. Imbibition is restricted to cocurrent flow. Despite a marked difference in rock properties such as permeability and porosity, we find similar trends in saturation profiles and weight gain versus time functions. Imbibition in diatomite is relatively rapid when initial water saturation is low due to large capillary forces. Using a non-linear regression analysis together with the experimental data, the capillary pressure and water relative permeability curves are determined for the diatomite in the water-air system. The results given for displacement profiles by numerical simulation match the experimental results.},

}

Y. Wang, A. R. Kovscek, and W. E. Brigham. A Study of the Effect of Mobility Ratios on Pattern Displacement Behavior. Technical report, Stanford University, CA, USA, December 1998.
[pdf]
Keywords: Mobility Control, Sweep Efficiency, Simulation.

Abstract

It is well known, for unit mobility ratio, that the areal sweep efficiency of a staggered line drive pattern is always better than a five-spot pattern. However, this observation does not hold for very favorable mobility ratios. I studied the effect of mobility ratios on pattern behavior by the means of simulation using a streamline simulator. In this report, I present simulation results and, with the help of streamline and saturation distributions, explain the differences between displacements with unit and favorable mobility ratios. Simulations compare well with experiments conducted elsewhere. Accurate definition of breakthrough time is also discussed for multiphase, streamline, simulation results. The exact definition of breakthrough is difficult due to physical dispersion in experiments and numerical dispersion in simulations.

BibTex Entry:

@TECHREPORT{TR115,
TITLE ={A Study of the Effect of Mobility Ratios on Pattern Displacement Behavior},
AUTHOR ={Y. Wang and A. R. Kovscek and W. E. Brigham},
YEAR ={1998},
MONTH =dec,
INSTITUTION = {Stanford University, CA, USA},
KEYWORDS ={Mobility Control, Sweep Efficiency, Simulation},
URL ={http://ekofisk.stanford.edu/supria/publications/public/tr115.pdf},
ABSTRACT ={It is well known, for unit mobility ratio, that the areal sweep efficiency of a staggered line drive pattern is always better than a five-spot pattern. However, this observation does not hold for very favorable mobility ratios. I studied the effect of mobility ratios on pattern behavior by the means of simulation using a streamline simulator. In this report, I present simulation results and, with the help of streamline and saturation distributions, explain the differences between displacements with unit and favorable mobility ratios. Simulations compare well with experiments conducted elsewhere. Accurate definition of breakthrough time is also discussed for multiphase, streamline, simulation results. The exact definition of breakthrough is difficult due to physical dispersion in experiments and numerical dispersion in simulations.},

}

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Last modification: Thu Dec 02 13:25:51 2004
Maintained by Herve Gross, SUPRI-A PhD Candidate.

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Publications of year 1998

Conference articles

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Internal reports

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