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Publications of year 2000

Conference articles

  1. O. G. Apaydin and A. R. Kovscek. Transient Foam Flow in Homogeneous Porous Media: Surfactant Concentration and Capillary End Effects.. In , Tulsa, OK, USA, April 2000.
    [pdf]
    Keywords: Foam, Mobility Control, Interfacial Tension.

    Abstract

    Foaming injected gas is a useful and promising technique for achieving mobility control in porous media. Typically, such foams are aqueous. In the presence of foam, gas and liquid flow behavior is determined by bubble size or foam texture. The thin-liquid films that separate foam into bubbles must be relatively stable for a foam to be finely textured and thereby be effective as a displacing or blocking agent. Film stability is a strong function of surfactant concentration and type. This work studies foam flow behavior at a variety of surfactant concentrations using experiments and a numerical model. Thus, the foam behavior examined spans from strong to weak. Specifically, a suite of foam displacements over a range of surfactant concentrations were monitored in a roughly 7 mm2, one-dimensional sandpack using X-ray computed tomography (CT). Sequential pressure taps were employed to measure flow resistance. Nitrogen was the gas and an alpha olefin sulfonate (AOS 1416) in brine was the foamer. Surfactant concentrations studied varied from 0.005 to 1 wt%. Because foam mobility depends strongly upon its texture, a bubble population balance model is both useful and necessary to describe the experimental results thoroughly and self consistently. Excellent agreement is found between experiment and theory.




    Annotation: 3-5 April 2000
    BibTex Entry:
    @CONFERENCE{SPE59286,
TITLE ={Transient Foam Flow in Homogeneous Porous Media: Surfactant Concentration and Capillary End Effects.},
AUTHOR ={O. G. Apaydin and A. R. Kovscek},
JOURNAL={SPE/DOE Improved Oil Recovery Symposium},
year ={2000},
month =apr,
address ={Tulsa, OK, USA},
URL ={http://ekofisk.stanford.edu/supria/publications/public/spe59286.pdf},
ABSTRACT ={Foaming injected gas is a useful and promising technique for achieving mobility control in porous media. Typically, such foams are aqueous. In the presence of foam, gas and liquid flow behavior is determined by bubble size or foam texture. The thin-liquid films that separate foam into bubbles must be relatively stable for a foam to be finely textured and thereby be effective as a displacing or blocking agent. Film stability is a strong function of surfactant concentration and type. This work studies foam flow behavior at a variety of surfactant concentrations using experiments and a numerical model. Thus, the foam behavior examined spans from strong to weak. Specifically, a suite of foam displacements over a range of surfactant concentrations were monitored in a roughly 7 mm2, one-dimensional sandpack using X-ray computed tomography (CT). Sequential pressure taps were employed to measure flow resistance. Nitrogen was the gas and an alpha olefin sulfonate (AOS 1416) in brine was the foamer. Surfactant concentrations studied varied from 0.005 to 1 wt%. Because foam mobility depends strongly upon its texture, a bubble population balance model is both useful and necessary to describe the experimental results thoroughly and self consistently. Excellent agreement is found between experiment and theory.},
annote ={3-5 April 2000},
KEYWORDS ={Foam, Mobility Control, Interfacial Tension},

}
  2. E. R. Rangel-German and A. R. Kovscek. Matrix-Fracture Interactions in Single Matrix Blocks. In , Stanford University, CA, USA, January 2000.
    [pdf]
    Keywords: Fractures, Imbibition, Experimental Work.

    Abstract

    Capillary imbibition is an important mechanism during water reinjection in fractured porous media. Using an X-ray computerized tomography (CT) scanner, and a novel, CT-compatible core holder, we performed a number of experiments to study air expulsion from rock samples by capillary imbibition of water in a three-dimensional geometry. Different injection rates and fracture apertures were utilized. The existence of two flow periods during imbibition by the matrix was observed. The early-time period can be understood as an infinite acting media and the square root of time model of imbibition with the appropriate characteristic time and length can be used. Although the late-time period has not been analyzed fully, a set of both characteristic times and lengths is proposed. Two different fracture flow regimes were also identified. The first one, named “filling-fracture” shows a variable length plane source due to relatively slow water flow through fractures; the second flow regime, named “instantly-filled fracture”, where the time to fill the fracture is much less than the imbibition time, shows a constant plane source imbibition. The behavior of the second regime is very similar to that observed in both counter current and cocurrent one-dimensional imbibition experiments reported previously in the literature.



    BibTex Entry:
    @CONFERENCE{ERGerman_2000,
TITLE ={Matrix-Fracture Interactions in Single Matrix Blocks},
AUTHOR ={E. R. Rangel-German and A. R. Kovscek},
JOURNAL={Stanford Geothermal Reservoir Engineering Workshop},
year ={2000},
month =jan,
address ={Stanford University, CA, USA},
KEYWORDS ={Fractures, Imbibition, Experimental Work},
URL ={http://ekofisk.stanford.edu/supria/publications/public/geotherm00.pdf},
ABSTRACT ={Capillary imbibition is an important mechanism during water reinjection in fractured porous media. Using an X-ray computerized tomography (CT) scanner, and a novel, CT-compatible core holder, we performed a number of experiments to study air expulsion from rock samples by capillary imbibition of water in a three-dimensional geometry. Different injection rates and fracture apertures were utilized. The existence of two flow periods during imbibition by the matrix was observed. The early-time period can be understood as an infinite acting media and the square root of time model of imbibition with the appropriate characteristic time and length can be used. Although the late-time period has not been analyzed fully, a set of both characteristic times and lengths is proposed. Two different fracture flow regimes were also identified. The first one, named “filling-fracture” shows a variable length plane source due to relatively slow water flow through fractures; the second flow regime, named “instantly-filled fracture”, where the time to fill the fracture is much less than the imbibition time, shows a constant plane source imbibition. The behavior of the second regime is very similar to that observed in both counter current and cocurrent one-dimensional imbibition experiments reported previously in the literature.},

}
  3. Y. Wang and A. R. Kovscek. A Streamline Approach for History-Matching Production Data. In , Tulsa, OK, USA, April 2000.
    [pdf]
    Keywords: Streamlines, History-Matching, Inverse Problems.

    Abstract

    This study proposes and develops a streamline approach for inferring field-scale effective permeability distributions based on dynamic production data including producer water-cut curve, well pressures, and rates. The approach simplifies the history-matching process significantly. The basic idea is to relate the fractional-flow curve at a producer to the water breakthrough of individual streamlines. By adjusting the effective permeability along streamlines, the breakthrough time of each streamline is found that reproduces the reference producer fractional-flow curve. Then the permeability modification along each streamline is mapped onto cells of the simulation grid. Modifying effective permeability at the streamline level greatly reduces the size of the inverse problem compared to modifications at the gridblock level. The approach outlined here is relatively direct and greatly reduces the computational work by eliminating the repeated inversion of a system of equations. It works well for reservoirs where heterogeneity determines flow patterns. Example cases illustrate computational efficiency, generality, and robustness of the proposed procedure. Advantages and limitations of this work, and the scope of future study, are also discussed.



    BibTex Entry:
    @CONFERENCE{SPE59370,
TITLE ={A Streamline Approach for History-Matching Production Data},
AUTHOR ={Y. Wang and A. R. Kovscek},
JOURNAL={SPE/DOE Improved Oil Recovery Symposium},
year ={2000},
month =apr,
address ={Tulsa, OK, USA},
KEYWORDS ={Streamlines, History-Matching, Inverse Problems},
URL ={http://ekofisk.stanford.edu/supria/publications/public/spe59370text.pdf},
ABSTRACT ={This study proposes and develops a streamline approach for inferring field-scale effective permeability distributions based on dynamic production data including producer water-cut curve, well pressures, and rates. The approach simplifies the history-matching process significantly. The basic idea is to relate the fractional-flow curve at a producer to the water breakthrough of individual streamlines. By adjusting the effective permeability along streamlines, the breakthrough time of each streamline is found that reproduces the reference producer fractional-flow curve. Then the permeability modification along each streamline is mapped onto cells of the simulation grid. Modifying effective permeability at the streamline level greatly reduces the size of the inverse problem compared to modifications at the gridblock level. The approach outlined here is relatively direct and greatly reduces the computational work by eliminating the repeated inversion of a system of equations. It works well for reservoirs where heterogeneity determines flow patterns. Example cases illustrate computational efficiency, generality, and robustness of the proposed procedure. Advantages and limitations of this work, and the scope of future study, are also discussed.},

}

Internal reports

  1. O. G. Apaydin and A. R. Kovscek. Surfactant Concentration and End Effects on Foam Flow in Porous Media. Technical report, Stanford University, CA, USA, October 2000.
    [pdf]
    Keywords: Foam, Mobility Control, Experimental Work.

    Abstract

    Foaming injected gas is a useful and promising technique for achieving mobility control in porous media. Typically, such foams are aqueous. In the presence of foam, gas and liquid flow behavior is determined by bubble size or foam texture. The thin-liquid films that separate foam into bubbles must be relatively stable for a foam to be finely textured and thereby be effective as a displacing or blocking agent. Film stability is a strong function of surfactant concentration and type. This work studies foam flow behavior at a variety of surfactant concentrations using experiments and a numerical model. Thus, the foam behavior examined spans from strong to weak. Specifically, a suite of foam displacements over a range of surfactant concentrations in a roughly 7 µm2, one-dimensional sandpack are monitored using X-ray computed tomography (CT). Sequential pressure taps are employed to measure flow resistance. Nitrogen is the gas and an alpha olefin sulfonate (AOS 1416) in brine is the foamer. Surfactant concentrations studied vary from 0.005 to 1 wt%. Because foam mobility depends strongly upon its texture, a bubble population balance model is both useful and necessary to describe the experimental results thoroughly and self consistently. Excellent agreement is found between experiment and theory.



    BibTex Entry:
    @TECHREPORT{TR120,
TITLE ={Surfactant Concentration and End Effects on Foam Flow in Porous Media},
AUTHOR ={O. G. Apaydin and A. R. Kovscek},
YEAR ={2000},
MONTH =oct,
INSTITUTION ={Stanford University, CA, USA},
KEYWORDS ={Foam, Mobility Control, Experimental Work},
URL ={http://ekofisk.stanford.edu/supria/publications/public/tr120.pdf},
ABSTRACT ={Foaming injected gas is a useful and promising technique for achieving mobility control in porous media. Typically, such foams are aqueous. In the presence of foam, gas and liquid flow behavior is determined by bubble size or foam texture. The thin-liquid films that separate foam into bubbles must be relatively stable for a foam to be finely textured and thereby be effective as a displacing or blocking agent. Film stability is a strong function of surfactant concentration and type. This work studies foam flow behavior at a variety of surfactant concentrations using experiments and a numerical model. Thus, the foam behavior examined spans from strong to weak. Specifically, a suite of foam displacements over a range of surfactant concentrations in a roughly 7 µm2, one-dimensional sandpack are monitored using X-ray computed tomography (CT). Sequential pressure taps are employed to measure flow resistance. Nitrogen is the gas and an alpha olefin sulfonate (AOS 1416) in brine is the foamer. Surfactant concentrations studied vary from 0.005 to 1 wt%. Because foam mobility depends strongly upon its texture, a bubble population balance model is both useful and necessary to describe the experimental results thoroughly and self consistently. Excellent agreement is found between experiment and theory.},

}
  2. W. E. Brigham. Doublets and Other Allied Well Problems.. Technical report, Stanford University, CA, USA, December 2000.
    [pdf]
    Keywords: Sweep Efficiency, Well Models. BibTex Entry:
    @TECHREPORT{TR122,
TITLE ={Doublets and Other Allied Well Problems.},
AUTHOR ={W. E. Brigham},
YEAR ={2000},
MONTH =dec,
INSTITUTION = {Stanford University, CA, USA},
KEYWORDS ={Sweep Efficiency, Well Models},
URL ={http://ekofisk.stanford.edu/supria/publications/public/tr122.pdf},

}
  3. D. Zhou, L. Jia, J. Kamath, and A. R. Kovscek. Scaling of Counter-Current Imbibition Processes in Low Permeability Porous Media.. Technical report, Stanford University, CA, USA, December 2000.
    [pdf]
    Keywords: Imbibition, Diatomites, Tomography, Experimental Work.

    Abstract

    Oil recovery from low permeability reservoirs is strategically important because of the large resources locked in such formations. Imbibition is fundamental to oil recovery from such reservoirs under most secondary and improved recovery processes of practical interest. It is also characteristic of porous medium wettability. The rate and the extent of imbibition depend critically on the viscosity of the wetting and nonwetting phases. In this study, we present our recent work on imaging imbibition in low permeability porous media (diatomite) with X-ray computed tomography. The viscosity ratio between nonwetting and wetting fluids is varied over several orders of magnitude yielding different levels of imbibition performance. We also perform a mathematical analysis of counter-current imbibition processes and develop a modified scaling group incorporating the mobility ratio. This modified group is physically based and appears to improve scaling accuracy of countercurrent imbibition significantly.



    BibTex Entry:
    @TECHREPORT{TR121b,
TITLE ={Scaling of Counter-Current Imbibition Processes in Low Permeability Porous Media.},
AUTHOR ={D. Zhou and L. Jia and J. Kamath and A. R. Kovscek},
YEAR ={2000},
MONTH =dec,
INSTITUTION = {Stanford University, CA, USA},
KEYWORDS ={Imbibition, Diatomites, Tomography, Experimental Work},
URL ={http://ekofisk.stanford.edu/supria/publications/public/tr121b.pdf},
ABSTRACT ={Oil recovery from low permeability reservoirs is strategically important because of the large resources locked in such formations. Imbibition is fundamental to oil recovery from such reservoirs under most secondary and improved recovery processes of practical interest. It is also characteristic of porous medium wettability. The rate and the extent of imbibition depend critically on the viscosity of the wetting and nonwetting phases. In this study, we present our recent work on imaging imbibition in low permeability porous media (diatomite) with X-ray computed tomography. The viscosity ratio between nonwetting and wetting fluids is varied over several orders of magnitude yielding different levels of imbibition performance. We also perform a mathematical analysis of counter-current imbibition processes and develop a modified scaling group incorporating the mobility ratio. This modified group is physically based and appears to improve scaling accuracy of countercurrent imbibition significantly.},

}


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Last modification: Thu Dec 02 13:25:51 2004
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