Performance of wellhead chokes during sub-critical flow of gas condensates Hazim Al-Attar ⁎ Department of Chemical and Petroleum Engineering, University of United Arab Emirates, 17555 Al Ain, United Arab Emirates Received 6 June 2007; accepted 21 August 2007 Abstract Field data from three key wells producing from a gas condensate reservoir located in the Middle East were implemented to test a new plotting technique to describe the sub-critical flow behavior of gas condensates through wellhead chokes. Empirical correlations were developed for eight different choke sizes between 24/64 in. and 128/64 in. These correlations can be applied to predict gas flow rates under wide range of flow conditions usually encountered during the flow of gas condensates through wellhead chokes. Using the proposed plotting technique, all ninety seven data points were found to follow a clear trend which can accurately predict the observed gas flow rates under the specified range of parameters involved in this study. In an attempt to develop a general correlation which includes the choke size as a variable, the same data points were used in a non-linear regression analysis. Based on five statistical measures, the results of gas flow rates calculated by the general formula were compared with those calculated by the individual choke size formulae, and the latter were found superior. This paper presents a simple, yet accurate, method of predicting gas flow rates for a specified choke size under sub-critical flow conditions through chokes. It can also be used to select the choke size necessary to achieve a required gas flow rate. The results of this work are very important in the design and implementation of deliverability tests, pressure transient tests, well control, and long-term well production of gas condensates. © 2007 Elsevier B.V. All rights reserved. Keywords: choke; sub-critical flow; gas; condensates; performance; wellhead 1. Introduction Wellhead chokes are widely used in the petroleum industry to control flow rate from wells, to maintain stable pressure downstream from the choke, and to provide the necessary backpressure to a reservoir to avoid formation damage from excessive drawdown. Consequently, it is extremely important for petroleum engineers to be able to select the correct choke size for a given application. This is only possible through accurate modeling of choke performance. Two types of gas–liquid flow can exist in a choke; critical and sub-critical flow. During critical flow, the velocity of the flowing fluids through the choke reaches the sonic velocity for the two-phase fluid and the flow rate becomes independent of the downstream pressure. Conversely, in sub-critical flow the flow rate depends on the pressure differential and changes in the downstream pressure affect the upstream pressure. Fortunati (1972) reported that a majority of wells in the field operates under sub-critical conditions. However, most of the Available online at www.sciencedirect.com Journal of Petroleum Science and Engineering 60 (2008) 205 – 212 www.elsevier.com/locate/petrol ⁎ Tel.: 971 33040; fax: 971 37624262. E-mail address: Hazim.Alattar@uaeu.ac.ae. 0920-4105/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.petrol.2007.08.001