It is possible to find in the literature, some papers concerning the two phase flow through the wellhead chokes, but nearly all these contributions concern only the critical flow.

The critical flow, when only the gas is concerned, happens around a choke downstream - upstream pressure ratio of about 0,5, but this condition is no more valid as the flow is two phase (gas and liquid). The velocity of a two phase flow, both critical and subcritical, is greatly depending from the gas concentration in respect to the mixture, and the downstream - upstream pressure ratio can be also lower than 0.225. pressure ratio can be also lower than 0.225.The practical cases, as experienced during several years, are nearly all in the subcritical flow field, and in the present paper, a simple formula is given for calculating the rates through the wellhead chokes, covering both the critical and subcritical flow fields.

The equation below reported, can be easily also developed through a computer program.

In the text, the number between square brackets, refer to the literature, and the numbers between round brackets, refer to the equations.

This paper is mainly intended for practical purposes, some unavoidable calculation developments were confined in the Appendixes.

A full relief was given to the illustrative numerical examples and through all the paper the metric system of units is used.


Since recently two phase flow is receiving more and more attention by the researchers working in the oil industry. It can be said that no one month passes without appearing in the literature, scattered over the world, a contribution concerning this item. The impulse to these researches came from the observation that the pressure drop through a pipe, when flowing a gas/oil mixture, can be also ten times more than that due to a single phase flow.

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