Performance of wellhead chokes during sub-critical flow of gas condensates

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.