Estimating the Static Bottom-Hole Pressure of Gas Wells by Top Node Calculation Using Apparent Molecular Weight Profiling

  • Nasser M. Al-HajriEmail author
  • Sidqi A. Abu-Khamsin
  • Mohammed D. Al-Ajmi
Research Article - Petroleum Engineering


A reservoir’s static bottom-hole pressures (SBHPs) are an integral component of many reservoir evaluation disciplines. The SBHP is normally acquired through gauge measurements; however, this method has disadvantages such as cost and risk. Accordingly, the ability to accurately estimate the SBHP would provide a cost-effective and safe alternative to well intervention. In this work, a new calculation method is introduced to predict the SBHP of a natural gas well. This method differs from existing methods by utilizing the apparent molecular weight profiling concept. Based on the inputs of pressure and temperature gradient data, an iterative calculation scheme is applied to produce a well-specific molecular weight profile. This profile is used along with a modified form of the equation of state to perform top node pressure calculations and ultimately predict the SBHP for gas wells. The top node method was tested rigorously using 75 case studies from five different fields and reservoirs and the prediction results were compared with actual field measurements. Also, the prediction performance of the top node method was compared with those of four previous methods (Rawlins and Schellhardt, Rzasa and Katz, Sukkar and Cornell, and Cullender and Smith). The results of this work showed that the top node calculation method was accurate in predicting the SBHP and has outperformed the four previous methods.


Reservoir static bottom-hole pressure Apparent molecular weight profiling Top node calculation Pressure and temperature gradient 


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  1. 1.
    Rawlins, E.L.; Shellhardt, M.A.: Back-Pressure Data on Natural-Gas Wells and Their Application to Production Practices. U.S. Bureau of Mines Monograph 7 (1935)Google Scholar
  2. 2.
    Rzasa, M.J.; Katz, D.L.: Calculation of static pressure gradient in gas wells. Pet. Trans. AIME 160(1), 100–106 (1945). CrossRefGoogle Scholar
  3. 3.
    Sukkar, Y.K.; Cornell, D.: Direct calculation of bottom-hole pressures in natural gas wells. Trans. AIME 204, 43–48 (1955)Google Scholar
  4. 4.
    Cullender, M.H.; Smith, R.V.: Practical solution of gas flow equations for wells and pipelines with large temperature gradients. Trans. AIME 207, 281–287 (1956)Google Scholar
  5. 5.
    Michael, J.R.; Donald, L.K.: The Coexistence of Liquid and Vapor Phases at Pressures Above 10,000 Psia. Paper SPE-950119-G (1950)Google Scholar
  6. 6.
    Cullender, M.H.; Smith, R.V.: Practical solution of gas flow equations for wells and pipelines with large temperature gradients. Trans. AIME 207, 281–287 (1956). CrossRefGoogle Scholar
  7. 7.
    Olufemi, A.; Adesina, F.A.S.; Olugbenga, F.: Predictive tool for bottom-hole pressure in multiphase flowing wells. Pap. Pet. Coal 50(3), 67–73 (2008)Google Scholar
  8. 8.
    Agbi, D.: Calculation of bottom-hole pressures in single phase gas wells from wellhead measurements. In: Paper PETSOC-75-09 Presented at the Annual Technical Meeting, June 11–13, Banff (1975)Google Scholar
  9. 9.
    Fang, C.-S.: Calculations of bottom-hole pressure of gas wells using an equation of state. Paper SPE-12559-MS (1983)Google Scholar
  10. 10.
    Barrufet, M.A.; Rasool, A.; Aggour, M.: Prediction of bottomhole flowing pressures in multiphase systems using a thermodynamic equation of state. In: Paper SPE-29479-MS Presented at the SPE Production Operations Symposium, 2–4 April, Oklahoma City, Oklahoma (1995)Google Scholar
  11. 11.
    Guo, B.: Use of wellhead-pressure data to establish well-inflow performance relationship. In: Paper SPE-72372-MS Presented at the SPE Eastern Regional Meeting, 17–19 October, Canton, Ohio (2001)Google Scholar
  12. 12.
    Nurafza, P.R.: Estimation of static bottom hole pressure from well-head shut-in pressure for a supercritical fluid in a depleted HP/HT reservoir. In: Paper SPE-124578-MS Presented at the Offshore Europe, 8–11 September, Aberdeen, UK (2009)Google Scholar
  13. 13.
    Beggs, D.H.; Brill, J.P.: A study of two-phase flow in inclined pipes. J. Pet. Technol. 25(5), 607–617 (1973). CrossRefGoogle Scholar
  14. 14.
    Standing, M.B.; Katz, D.L.: Density of natural gases. In: Transactions of the American Institute of Mining and Metallurgical Engineers, No. 142, SPE-942140-G, 140–149. American Institute of Mining and Metallurgical Engineers Inc., New York (1942).
  15. 15.
    Sutton, R.P.: Fundamentals PVT calculations for associated and gas/condensate natural-gas systems. SPE Reserv. Eng. Eval. J. 10(3), 270–284 (2007). CrossRefGoogle Scholar
  16. 16.
    Dranchuk, P.M.; Abou-Kassem, J.H.: Calculation of Z factor for natural gases using equation of state. J. Can. Pet. Technol. 14(3), 34–36 (1975). CrossRefGoogle Scholar
  17. 17.
    Mahmoud, M.: Development of a new correlation of gas compressibility factor (Z-factor) for high pressure gas reservoirs. J. Energy Resour. Technol. 136, 1–11 (2014). CrossRefGoogle Scholar
  18. 18.
    Bukacek, R.F.: Equilibrium Moisture Content of Natural Gases, pp. 198–200. Research Bulletin IGT, Chicago (1959)Google Scholar

Copyright information

© King Fahd University of Petroleum & Minerals 2018

Authors and Affiliations

  • Nasser M. Al-Hajri
    • 1
    Email author
  • Sidqi A. Abu-Khamsin
    • 2
  • Mohammed D. Al-Ajmi
    • 1
  1. 1.Saudi AramcoDhahranSaudi Arabia
  2. 2.King Fahd University of Petroleum and MineralsDhahranSaudi Arabia

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