The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform

Tongke Zhou - One of the best experts on this subject based on the ideXlab platform.

  • experimental study on the dynamic filtration control performance of n2 liquid co2 foam in porous media
    Fuel, 2017
    Co-Authors: Chao Zhang, Dasha Shi, Chao Zheng, Tongke Zhou
    Abstract:

    Abstract Liquid CO 2 has been successfully used as a fracturing fluid and injected into rock formations to enhance oil and gas production. However, the difficulty in controlling the filtration of liquid CO 2 in porous media limits its application. The goal of this study is to investigate the dynamic filtration control performance of N 2 /liquid CO 2 foam with a fluorochemical (HFE) as stabilizer. A laboratory apparatus has been specially designed and built for the generation of N 2 /liquid CO 2 foams and the measurement of their viscosity and filtration rate under high pressure (10–25 MPa). The test results show that after liquid CO 2 and HFE were mixed with N 2 , the N 2 /liquid CO 2 foams were generated and showed significant viscosity improvement compared to liquid CO 2 . The foams exhibited better filtration control performance compared to liquid CO 2 and liquid CO 2  + N 2 systems. Although the addition of HFE did not result in the formation of filter cake, the foam showed a wall-building behavior, which could be explained by the CO 2 phase change in porous media. As foam quality increased from 28% to 92%, the leakoff coefficient and Spurt Loss volume first decreased until the foam became unstable and changed into mist flow. The leakoff coefficient of foam increased with the increase in permeability of porous media. For foam with the quality of about 50–80%, a change of 2 orders of magnitude in permeability resulted in a change of 1 order of magnitude in leakoff coefficient. At high pressure difference, lower initial quality foam (∼30%) showed better filtration performance than higher initial quality foam (∼80%). When the pressure difference was high enough to cause the CO 2 phase change from liquid to gas in the porous media, the initial foam damage after filtration became obvious, but the damage could be eliminated with time by gas return flow. Thus, by using N 2 /liquid CO 2 foam in porous media, the fluid filtration behavior could be controlled without damage.

  • Experimental study on the dynamic filtration control performance of N2/liquid CO2 foam in porous media
    Fuel, 2017
    Co-Authors: Chao Zhang, Dashan Shi, Zheng Chao, Tongke Zhou
    Abstract:

    Abstract Liquid CO 2 has been successfully used as a fracturing fluid and injected into rock formations to enhance oil and gas production. However, the difficulty in controlling the filtration of liquid CO 2 in porous media limits its application. The goal of this study is to investigate the dynamic filtration control performance of N 2 /liquid CO 2 foam with a fluorochemical (HFE) as stabilizer. A laboratory apparatus has been specially designed and built for the generation of N 2 /liquid CO 2 foams and the measurement of their viscosity and filtration rate under high pressure (10–25 MPa). The test results show that after liquid CO 2 and HFE were mixed with N 2 , the N 2 /liquid CO 2 foams were generated and showed significant viscosity improvement compared to liquid CO 2 . The foams exhibited better filtration control performance compared to liquid CO 2 and liquid CO 2  + N 2 systems. Although the addition of HFE did not result in the formation of filter cake, the foam showed a wall-building behavior, which could be explained by the CO 2 phase change in porous media. As foam quality increased from 28% to 92%, the leakoff coefficient and Spurt Loss volume first decreased until the foam became unstable and changed into mist flow. The leakoff coefficient of foam increased with the increase in permeability of porous media. For foam with the quality of about 50–80%, a change of 2 orders of magnitude in permeability resulted in a change of 1 order of magnitude in leakoff coefficient. At high pressure difference, lower initial quality foam (∼30%) showed better filtration performance than higher initial quality foam (∼80%). When the pressure difference was high enough to cause the CO 2 phase change from liquid to gas in the porous media, the initial foam damage after filtration became obvious, but the damage could be eliminated with time by gas return flow. Thus, by using N 2 /liquid CO 2 foam in porous media, the fluid filtration behavior could be controlled without damage.

R. Henry Jacot - One of the best experts on this subject based on the ideXlab platform.

  • Fracture Pressure-Slope Analysis for TSOs in High-Permeability Formations
    Spe Production & Facilities, 2002
    Co-Authors: Jeffrey E. Smith, Bruce R. Meyer, R. Henry Jacot
    Abstract:

    The relative popularity and success of the frac-pack technique in hydraulic fracturing has resulted in some misconceptions regarding the objective, procedure, and pressure analysis after a screenout. This paper addresses frac-pack procedures and the pressure response after a tip screenout (TSO). An analytical method has been developed for analyzing pressure-slope behavior after a TSO in high-permeability formations. These equations incorporate the first order parameters affecting the fracture pressure, rate of pressure change (derivative), and pressure-slope behaviors after a screenout. The fundamental equations for pressure-slope analysis are similar to those originally developed by Nolte for pressure-decline analysis. The major difference is that after the fracture stops propagating (i.e., after a TSO), the injection rate is not zero. Consequently, if the injection rate is greater than the leakoff rate, the fracture volume and net pressure (constant compliance) must increase. If the injection rate falls below the leakoff rate, the fracture net pressure must decrease. Although analytical equations will not replace 3D fracturing simulators normally used for design and real-time history matching, they do provide insight into the major parameters affecting pressure behavior after a TSO without running a numerical simulator. The analytical equations presented in this paper demonstrate why pressure slopes after a screenout are typically much greater than unity for low-efficiency fractures. A generalized set of equations is presented for analyzing the pressure-slope behavior after a screenout. Numerous graphs are provided that illustrate the parametric effects of fracture efficiency, Spurt Loss, and fracture net pressure at the time of a screenout on the pressure, derivative, and slope behaviors after a TSO. Comparisons of the analytical pressure-slope equations with a 3D fracturing simulator are presented to show the analysis' application. A new methodology of frac-pack post-analysis is presented using the pressure slope technique. This methodology uses the pressure slope during a screenout as a check on the minifracture and fracture efficiency. Two frac-pack cases with bottomhole data are analyzed with a 3D hydraulic fracturing simulator to illustrate the pressure-slope analysis for low efficiency fractures.

  • The Effect of Fluid Loss During Fracture Calibration Tests on the Main Treatment
    All Days, 2000
    Co-Authors: Bruce R. Meyer, R. Henry Jacot
    Abstract:

    Abstract Fracture calibration tests (minifracs) are very successful methods for providing estimates of the fluid efficiency, closure pressure, fracture geometry and leakoff coefficient prior to the main treatment. The pressure decline data is normally analyzed using a Nolte type method for calibration and redesign of the main treatment. Many times it has been observed that the main treatment has a higher efficiency (less fluid Loss) than the minifrac which can adversely impact the fracture treatment. This paper addresses the effect of fluid Loss during fracture calibration tests on the main treatment. An analytical method for leakoff controlled by the filter cake and/or filtrate fluid has been developed for analyzing the effect of fluid Loss in the formation prior to the main treatment. The main treatment leakoff velocity and volume Loss equations ac-count for the effects of the minifrac fluid Loss behavior, including filter cake, Spurt Loss, mobility, time of fracture creation and relative fracture planes. This paper presents the foundation for a generalized set of equations quantifying the effects of the minifrac fluid Loss on the main treatment by conservation of mass and Darcy's law. Equations are formulated for the main treatment leakoff velocity and volume Loss. Numerous figures are provided that illustrate the parametric effects of the minifrac fluid Loss on the main treatment efficiency and fraction of pad volume. Introduction Smith1 et.al. in 2000 was one of the first to investigate the effect of the minifrac fluid Loss on the main treatment. Their paper evaluated laboratory and field data that contained multiple leakoff periods and provided some procedures for removing the filter cake by additional fluid injections. Although their paper provided a rationale for the discrepancy in the main treatment leakoff behavior, a quantitative mathematical formulation based on first order physics was not addressed. The work presented here formulates the governing equations for analyzing the effect of minifrac fluid Loss on the main treatment. The methodology implements the first order minifrac leakoff parameters affecting the main treatment fluid Loss. The formulation is based on the conservation of mass and Darcy's law. Graphs are presented which display the main treatment average leakoff velocity and fluid Loss volume factors as functions of the minifrac efficiency (dimensionless closure time), Spurt Loss, minifrac mobility and fracture area created during the minifrac. Various charts are also presented for determining the main treatment fracture efficiency and fraction of pad as a function of the minifrac efficiency, beta parameter and main treatment pump time. Theory This section summarizes the governing equations describing fluid Loss after a minifrac. Details of this methodology are given in the Appendices. The governing mass conservation, fluid velocity and fluid Loss volume equations are summarized in Appendix A. Appendix B presents the formulation for the governing leakoff velocity correlation for multiple injections and closures. Appendix C defines the Nolte function and time derivative relationships. All symbols are defined in the Appendices and Nomenclature. The governing equations for the leakoff velocity and volume Loss of the main treatment that accounts for the minifrac fluid Loss is summarized below. The basic assumption is that leakoff is controlled by the fracturing filtrate viscosity (CI coefficient) and/or an incompressible filter cake (CIII coefficient) and that the minifrac closes prior to pumping the main treatment. The analysis assumes that a minifrac was pumped prior to the main treatment for a time ofwith a created leakoff area ofand a closure time of. It is also assumed that fluid Loss (leakoff) is controlled by either the filter cake or filtrate viscosity and that these minifrac leakoff resistant mechanisms are present during the main treatment. Spurt Loss from the minifrac is included in the analysis.

  • Fracture Pressure Slope Analysis for TSO's in High-Permeability Formations
    All Days, 2000
    Co-Authors: Jeffrey E. Smith, Bruce R. Meyer, R. Henry Jacot
    Abstract:

    The relative popularity and success of the frac & pack technique in hydraulic fracturing has resulted in some misconceptions regarding the objective, procedure and pressure analysis after a screen-out. This paper addresses frac & pack procedures and the pressure response after a tip screen-out (TSO). An analytical method has been developed for analyzing pressure slope behavior after a TSO in high permeability formations. These equations incorporate the first order parameters affecting the fracture pressure, rate of change of pressure (derivative) and pressure slope behaviors after a screen-out. The fundamental equations for pressure slope analysis are similar to those originally developed by Nolte for pressure decline analysis. The major difference is that after the fracture stops propagating (i.e., after a TSO) the injection rate is not zero. Consequently, if the injection rate is greater than the leakoff rate, the fracture volume and net pressure (constant compliance) must increase. If the injection rate falls below the leakoff rate, the fracture net pressure must decrease. Although analytical equations will not replace three dimensional fracturing simulators normally used for design and real-time history matching, they do provide insight into the major parameters affecting pressure behavior after a TSO without running a numerical simulator. The analytical equations presented in this paper demonstrate why pressure slopes after a screen-out are typically much greater than unity for low efficiency fractures. A generalized set of equations is presented for analyzing the pressure slope behavior after a screen-out. Numerous graphs are provided which illustrate the parametric effects of fracture efficiency, Spurt Loss and fracture net pressure at the time of a screen-out on the pressure, derivative and slope behaviors after a TSO. Comparisons of the analytical pressure slope equations with a three dimensional fracturing simulator are presented to show the application of the analysis. A new methodology of frac & pack post analysis is presented using the pressure slope technique. This methodology utilizes the pressure slope during a screen-out as a check on the minifrac and fracture efficiency. Two frac & pack cases with bottomhole data are analyzed using a three dimensional hydraulic fracturing simulator to illustrate the pressure slope analysis for low efficiency fractures.

Chao Zhang - One of the best experts on this subject based on the ideXlab platform.

  • experimental study on the dynamic filtration control performance of n2 liquid co2 foam in porous media
    Fuel, 2017
    Co-Authors: Chao Zhang, Dasha Shi, Chao Zheng, Tongke Zhou
    Abstract:

    Abstract Liquid CO 2 has been successfully used as a fracturing fluid and injected into rock formations to enhance oil and gas production. However, the difficulty in controlling the filtration of liquid CO 2 in porous media limits its application. The goal of this study is to investigate the dynamic filtration control performance of N 2 /liquid CO 2 foam with a fluorochemical (HFE) as stabilizer. A laboratory apparatus has been specially designed and built for the generation of N 2 /liquid CO 2 foams and the measurement of their viscosity and filtration rate under high pressure (10–25 MPa). The test results show that after liquid CO 2 and HFE were mixed with N 2 , the N 2 /liquid CO 2 foams were generated and showed significant viscosity improvement compared to liquid CO 2 . The foams exhibited better filtration control performance compared to liquid CO 2 and liquid CO 2  + N 2 systems. Although the addition of HFE did not result in the formation of filter cake, the foam showed a wall-building behavior, which could be explained by the CO 2 phase change in porous media. As foam quality increased from 28% to 92%, the leakoff coefficient and Spurt Loss volume first decreased until the foam became unstable and changed into mist flow. The leakoff coefficient of foam increased with the increase in permeability of porous media. For foam with the quality of about 50–80%, a change of 2 orders of magnitude in permeability resulted in a change of 1 order of magnitude in leakoff coefficient. At high pressure difference, lower initial quality foam (∼30%) showed better filtration performance than higher initial quality foam (∼80%). When the pressure difference was high enough to cause the CO 2 phase change from liquid to gas in the porous media, the initial foam damage after filtration became obvious, but the damage could be eliminated with time by gas return flow. Thus, by using N 2 /liquid CO 2 foam in porous media, the fluid filtration behavior could be controlled without damage.

  • Experimental study on the dynamic filtration control performance of N2/liquid CO2 foam in porous media
    Fuel, 2017
    Co-Authors: Chao Zhang, Dashan Shi, Zheng Chao, Tongke Zhou
    Abstract:

    Abstract Liquid CO 2 has been successfully used as a fracturing fluid and injected into rock formations to enhance oil and gas production. However, the difficulty in controlling the filtration of liquid CO 2 in porous media limits its application. The goal of this study is to investigate the dynamic filtration control performance of N 2 /liquid CO 2 foam with a fluorochemical (HFE) as stabilizer. A laboratory apparatus has been specially designed and built for the generation of N 2 /liquid CO 2 foams and the measurement of their viscosity and filtration rate under high pressure (10–25 MPa). The test results show that after liquid CO 2 and HFE were mixed with N 2 , the N 2 /liquid CO 2 foams were generated and showed significant viscosity improvement compared to liquid CO 2 . The foams exhibited better filtration control performance compared to liquid CO 2 and liquid CO 2  + N 2 systems. Although the addition of HFE did not result in the formation of filter cake, the foam showed a wall-building behavior, which could be explained by the CO 2 phase change in porous media. As foam quality increased from 28% to 92%, the leakoff coefficient and Spurt Loss volume first decreased until the foam became unstable and changed into mist flow. The leakoff coefficient of foam increased with the increase in permeability of porous media. For foam with the quality of about 50–80%, a change of 2 orders of magnitude in permeability resulted in a change of 1 order of magnitude in leakoff coefficient. At high pressure difference, lower initial quality foam (∼30%) showed better filtration performance than higher initial quality foam (∼80%). When the pressure difference was high enough to cause the CO 2 phase change from liquid to gas in the porous media, the initial foam damage after filtration became obvious, but the damage could be eliminated with time by gas return flow. Thus, by using N 2 /liquid CO 2 foam in porous media, the fluid filtration behavior could be controlled without damage.

Jeffrey E. Smith - One of the best experts on this subject based on the ideXlab platform.

  • Fracture Pressure-Slope Analysis for TSOs in High-Permeability Formations
    Spe Production & Facilities, 2002
    Co-Authors: Jeffrey E. Smith, Bruce R. Meyer, R. Henry Jacot
    Abstract:

    The relative popularity and success of the frac-pack technique in hydraulic fracturing has resulted in some misconceptions regarding the objective, procedure, and pressure analysis after a screenout. This paper addresses frac-pack procedures and the pressure response after a tip screenout (TSO). An analytical method has been developed for analyzing pressure-slope behavior after a TSO in high-permeability formations. These equations incorporate the first order parameters affecting the fracture pressure, rate of pressure change (derivative), and pressure-slope behaviors after a screenout. The fundamental equations for pressure-slope analysis are similar to those originally developed by Nolte for pressure-decline analysis. The major difference is that after the fracture stops propagating (i.e., after a TSO), the injection rate is not zero. Consequently, if the injection rate is greater than the leakoff rate, the fracture volume and net pressure (constant compliance) must increase. If the injection rate falls below the leakoff rate, the fracture net pressure must decrease. Although analytical equations will not replace 3D fracturing simulators normally used for design and real-time history matching, they do provide insight into the major parameters affecting pressure behavior after a TSO without running a numerical simulator. The analytical equations presented in this paper demonstrate why pressure slopes after a screenout are typically much greater than unity for low-efficiency fractures. A generalized set of equations is presented for analyzing the pressure-slope behavior after a screenout. Numerous graphs are provided that illustrate the parametric effects of fracture efficiency, Spurt Loss, and fracture net pressure at the time of a screenout on the pressure, derivative, and slope behaviors after a TSO. Comparisons of the analytical pressure-slope equations with a 3D fracturing simulator are presented to show the analysis' application. A new methodology of frac-pack post-analysis is presented using the pressure slope technique. This methodology uses the pressure slope during a screenout as a check on the minifracture and fracture efficiency. Two frac-pack cases with bottomhole data are analyzed with a 3D hydraulic fracturing simulator to illustrate the pressure-slope analysis for low efficiency fractures.

  • Fracture Pressure Slope Analysis for TSO's in High-Permeability Formations
    All Days, 2000
    Co-Authors: Jeffrey E. Smith, Bruce R. Meyer, R. Henry Jacot
    Abstract:

    The relative popularity and success of the frac & pack technique in hydraulic fracturing has resulted in some misconceptions regarding the objective, procedure and pressure analysis after a screen-out. This paper addresses frac & pack procedures and the pressure response after a tip screen-out (TSO). An analytical method has been developed for analyzing pressure slope behavior after a TSO in high permeability formations. These equations incorporate the first order parameters affecting the fracture pressure, rate of change of pressure (derivative) and pressure slope behaviors after a screen-out. The fundamental equations for pressure slope analysis are similar to those originally developed by Nolte for pressure decline analysis. The major difference is that after the fracture stops propagating (i.e., after a TSO) the injection rate is not zero. Consequently, if the injection rate is greater than the leakoff rate, the fracture volume and net pressure (constant compliance) must increase. If the injection rate falls below the leakoff rate, the fracture net pressure must decrease. Although analytical equations will not replace three dimensional fracturing simulators normally used for design and real-time history matching, they do provide insight into the major parameters affecting pressure behavior after a TSO without running a numerical simulator. The analytical equations presented in this paper demonstrate why pressure slopes after a screen-out are typically much greater than unity for low efficiency fractures. A generalized set of equations is presented for analyzing the pressure slope behavior after a screen-out. Numerous graphs are provided which illustrate the parametric effects of fracture efficiency, Spurt Loss and fracture net pressure at the time of a screen-out on the pressure, derivative and slope behaviors after a TSO. Comparisons of the analytical pressure slope equations with a three dimensional fracturing simulator are presented to show the application of the analysis. A new methodology of frac & pack post analysis is presented using the pressure slope technique. This methodology utilizes the pressure slope during a screen-out as a check on the minifrac and fracture efficiency. Two frac & pack cases with bottomhole data are analyzed using a three dimensional hydraulic fracturing simulator to illustrate the pressure slope analysis for low efficiency fractures.

  • How Minifracs Alter Leakoff and Ways to Counteract It
    SPE International Symposium on Formation Damage Control, 2000
    Co-Authors: Jeffrey E. Smith, Sanjay Vitthal, James M. Mcgowen, Ron Dusterhoft
    Abstract:

    The analysis of minifracs in high-permeability formations has been the subject of several studies and debates. In many cases, the leakoff from the frac-pack appears to be less than that from the minifrac, which is normally conducted before the frac-pack. Consequently, the net pressure rise observed is less than the predicted net pressure based on the minifrac analysis. Rules of thumb have been developed to account for this apparent change in leakoff behavior. These rules include adjusting the Spurt Loss, choosing a latter-time closure press ire based on previous experience, and adjusting the observed fluid efficiency by an arbitrary factor. This paper attempts to provide a rationale for explaining the discrepancy between leakoff data collected from minifrac analysis and the observed frac-pack behavior. This paper also presents the results of laboratory experiments and field tests that show that the injection of a minifrac alters the observed fluid efficiency. Laboratcry tests evaluated the magnitude and character of the fluid Loss from subsequent injections of a frac-pack fluid. These tests were conducted with cores ranging from 100- to 3000-md permeability. Field results from trials in which two minifracs were injected in the same zone are also presented. These field data are from wells in the Gulf of Mexico (GOM) and from a well in North Africa, all of which experience high fluid-leakoffrates. The results from these injections show that the effects of minifrac fluid can alter fluid efficiency significantly. Finally, the paper proposes methods and best practices for measuring or counteracting this effect by altering the sequence of injections nto the formation. Laboratory data supports the philosophy behind these best practices. In addition, field data illustrate the success of this altered injection schedule.

Bruce R. Meyer - One of the best experts on this subject based on the ideXlab platform.

  • Fracture Pressure-Slope Analysis for TSOs in High-Permeability Formations
    Spe Production & Facilities, 2002
    Co-Authors: Jeffrey E. Smith, Bruce R. Meyer, R. Henry Jacot
    Abstract:

    The relative popularity and success of the frac-pack technique in hydraulic fracturing has resulted in some misconceptions regarding the objective, procedure, and pressure analysis after a screenout. This paper addresses frac-pack procedures and the pressure response after a tip screenout (TSO). An analytical method has been developed for analyzing pressure-slope behavior after a TSO in high-permeability formations. These equations incorporate the first order parameters affecting the fracture pressure, rate of pressure change (derivative), and pressure-slope behaviors after a screenout. The fundamental equations for pressure-slope analysis are similar to those originally developed by Nolte for pressure-decline analysis. The major difference is that after the fracture stops propagating (i.e., after a TSO), the injection rate is not zero. Consequently, if the injection rate is greater than the leakoff rate, the fracture volume and net pressure (constant compliance) must increase. If the injection rate falls below the leakoff rate, the fracture net pressure must decrease. Although analytical equations will not replace 3D fracturing simulators normally used for design and real-time history matching, they do provide insight into the major parameters affecting pressure behavior after a TSO without running a numerical simulator. The analytical equations presented in this paper demonstrate why pressure slopes after a screenout are typically much greater than unity for low-efficiency fractures. A generalized set of equations is presented for analyzing the pressure-slope behavior after a screenout. Numerous graphs are provided that illustrate the parametric effects of fracture efficiency, Spurt Loss, and fracture net pressure at the time of a screenout on the pressure, derivative, and slope behaviors after a TSO. Comparisons of the analytical pressure-slope equations with a 3D fracturing simulator are presented to show the analysis' application. A new methodology of frac-pack post-analysis is presented using the pressure slope technique. This methodology uses the pressure slope during a screenout as a check on the minifracture and fracture efficiency. Two frac-pack cases with bottomhole data are analyzed with a 3D hydraulic fracturing simulator to illustrate the pressure-slope analysis for low efficiency fractures.

  • The Effect of Fluid Loss During Fracture Calibration Tests on the Main Treatment
    All Days, 2000
    Co-Authors: Bruce R. Meyer, R. Henry Jacot
    Abstract:

    Abstract Fracture calibration tests (minifracs) are very successful methods for providing estimates of the fluid efficiency, closure pressure, fracture geometry and leakoff coefficient prior to the main treatment. The pressure decline data is normally analyzed using a Nolte type method for calibration and redesign of the main treatment. Many times it has been observed that the main treatment has a higher efficiency (less fluid Loss) than the minifrac which can adversely impact the fracture treatment. This paper addresses the effect of fluid Loss during fracture calibration tests on the main treatment. An analytical method for leakoff controlled by the filter cake and/or filtrate fluid has been developed for analyzing the effect of fluid Loss in the formation prior to the main treatment. The main treatment leakoff velocity and volume Loss equations ac-count for the effects of the minifrac fluid Loss behavior, including filter cake, Spurt Loss, mobility, time of fracture creation and relative fracture planes. This paper presents the foundation for a generalized set of equations quantifying the effects of the minifrac fluid Loss on the main treatment by conservation of mass and Darcy's law. Equations are formulated for the main treatment leakoff velocity and volume Loss. Numerous figures are provided that illustrate the parametric effects of the minifrac fluid Loss on the main treatment efficiency and fraction of pad volume. Introduction Smith1 et.al. in 2000 was one of the first to investigate the effect of the minifrac fluid Loss on the main treatment. Their paper evaluated laboratory and field data that contained multiple leakoff periods and provided some procedures for removing the filter cake by additional fluid injections. Although their paper provided a rationale for the discrepancy in the main treatment leakoff behavior, a quantitative mathematical formulation based on first order physics was not addressed. The work presented here formulates the governing equations for analyzing the effect of minifrac fluid Loss on the main treatment. The methodology implements the first order minifrac leakoff parameters affecting the main treatment fluid Loss. The formulation is based on the conservation of mass and Darcy's law. Graphs are presented which display the main treatment average leakoff velocity and fluid Loss volume factors as functions of the minifrac efficiency (dimensionless closure time), Spurt Loss, minifrac mobility and fracture area created during the minifrac. Various charts are also presented for determining the main treatment fracture efficiency and fraction of pad as a function of the minifrac efficiency, beta parameter and main treatment pump time. Theory This section summarizes the governing equations describing fluid Loss after a minifrac. Details of this methodology are given in the Appendices. The governing mass conservation, fluid velocity and fluid Loss volume equations are summarized in Appendix A. Appendix B presents the formulation for the governing leakoff velocity correlation for multiple injections and closures. Appendix C defines the Nolte function and time derivative relationships. All symbols are defined in the Appendices and Nomenclature. The governing equations for the leakoff velocity and volume Loss of the main treatment that accounts for the minifrac fluid Loss is summarized below. The basic assumption is that leakoff is controlled by the fracturing filtrate viscosity (CI coefficient) and/or an incompressible filter cake (CIII coefficient) and that the minifrac closes prior to pumping the main treatment. The analysis assumes that a minifrac was pumped prior to the main treatment for a time ofwith a created leakoff area ofand a closure time of. It is also assumed that fluid Loss (leakoff) is controlled by either the filter cake or filtrate viscosity and that these minifrac leakoff resistant mechanisms are present during the main treatment. Spurt Loss from the minifrac is included in the analysis.

  • Fracture Pressure Slope Analysis for TSO's in High-Permeability Formations
    All Days, 2000
    Co-Authors: Jeffrey E. Smith, Bruce R. Meyer, R. Henry Jacot
    Abstract:

    The relative popularity and success of the frac & pack technique in hydraulic fracturing has resulted in some misconceptions regarding the objective, procedure and pressure analysis after a screen-out. This paper addresses frac & pack procedures and the pressure response after a tip screen-out (TSO). An analytical method has been developed for analyzing pressure slope behavior after a TSO in high permeability formations. These equations incorporate the first order parameters affecting the fracture pressure, rate of change of pressure (derivative) and pressure slope behaviors after a screen-out. The fundamental equations for pressure slope analysis are similar to those originally developed by Nolte for pressure decline analysis. The major difference is that after the fracture stops propagating (i.e., after a TSO) the injection rate is not zero. Consequently, if the injection rate is greater than the leakoff rate, the fracture volume and net pressure (constant compliance) must increase. If the injection rate falls below the leakoff rate, the fracture net pressure must decrease. Although analytical equations will not replace three dimensional fracturing simulators normally used for design and real-time history matching, they do provide insight into the major parameters affecting pressure behavior after a TSO without running a numerical simulator. The analytical equations presented in this paper demonstrate why pressure slopes after a screen-out are typically much greater than unity for low efficiency fractures. A generalized set of equations is presented for analyzing the pressure slope behavior after a screen-out. Numerous graphs are provided which illustrate the parametric effects of fracture efficiency, Spurt Loss and fracture net pressure at the time of a screen-out on the pressure, derivative and slope behaviors after a TSO. Comparisons of the analytical pressure slope equations with a three dimensional fracturing simulator are presented to show the application of the analysis. A new methodology of frac & pack post analysis is presented using the pressure slope technique. This methodology utilizes the pressure slope during a screen-out as a check on the minifrac and fracture efficiency. Two frac & pack cases with bottomhole data are analyzed using a three dimensional hydraulic fracturing simulator to illustrate the pressure slope analysis for low efficiency fractures.