Two-Phase Flow through Wellhead Chokes

Abstract

This paper was prepared for the SPE-European Spring Meeting 1972 of the Society of Petroleum Engineers of AIME, held in Amsterdam, The Netherlands, May 16–18, 1972. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers, P.O. Box 228, The Hague, The Netherlands. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract 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. Introduction 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. Two phase flow is characterized by two functions, and, which are defined as: (1) Where: Fg = cross section area of the choke passage occupied by the gas phase - m2;Ft = Total cross section area of the choke passage-m2;qg = Gas rate at P2 and T = qog x B g -; m3/sec; qog = Gas rate at standard conditions Po and To - m3/sec; ql = liquid rate = q B at p and T-m3/sec; q = liquid rate at standard conditions Po and To - m3/sec. The multiphase flow can be as these patterns; - Dispersed flow;- Annular flow;- Wave flow;- Slug flow;- Plug flow;- Stratified flow;- Bubble flow; Generally the gas, when flowing with liquid (for ex. oil) through a pipe, slips over the liquid and, due to this condition and have different values, as shown on fig. 1, for the frequent case of plug flow (17).