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Relationship between formation water rate, equivalent penetration rate and volume flow rate of air in air drilling


Formation water invasion is the most troublesome problem associated with air drilling. However, it is not economical to apply mist drilling when only a small amount of water flows into wellbore from formation during air drilling. Formation water could be circulated out of the wellbore through increasing the gas injection rate. In this paper, the Angel model was modified by introducing Nikurade friction factor for the flow in coarse open holes and translating formation water rate into equivalent penetration rate. Thus the distribution of annular pressure and the relationship between minimum air injection rate and formation water rate were obtained. Real data verification indicated that the modified model is more accurate than the Angel model and can provide useful information for air drilling.

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Correspondence to Wang Kexiong.

Additional information

Wang Kexiong was born in 1965 and is studying for his PhD degree in the China University of Petroleum (Beijing). As an associate professor he is engaged in the research of oil/gas well engineering and geotechnical engineering. E-mail:

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Kexiong, W., Laibin, Z. & Hongwei, J. Relationship between formation water rate, equivalent penetration rate and volume flow rate of air in air drilling. Pet. Sci. 4, 62–65 (2007).

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Key words

  • Air drilling
  • Angel model
  • modified model
  • formation water rate
  • minimum volume flow rate
  • equivalent penetration rate