Evaluation of Methods Describing the Flow of Gas-liquid Mixture In Wells
Authors: Salim P.H. , Stanislav J.F. 
Published: March 2010

The simultaneous gas-liquid flow in pipes has been subjected to investigation over a long period of time. Results of this endeavor are of a general interest to petroleum, chemical and nuclear industries.

Numerous empirical correlations have been proposed to estimate the pressure drop and the liquid holdup for the flow of gas liquid mixtures. Only a few of these correlations are currently being used.

Attempts are continuously being made to develop methods based on the fundamental physical principles. Recently, Ansari et al. published a comprehensive mechanistic model which describes the hydrodynamics of gas-liquid flow in horizontal and vertical pipes.

The purpose of this study is to compare the individual performances of the selected correlations and models with data obtained from both the field and laboratory sources. Most of the field data were for the annular mist flow.

For the conditions considered, the methods based on the mechanistic concept were found to perform better than methods which are strictly of the empirical nature.

Introduction

A large number of correlations appeared in literature for dealing with various aspects of simultaneous gas-liquid flow in vertical pipes. Given the overall system complexity, the methods are typically restricted to the use of empirical correlations (mostly based on laboratory data). Applicability of these correlations to large scale systems has always been a reason for concern because any practical application involves extrapolation beyond the experimental conditions for which these correlations were obtained. Thus, a considerable engineering judgment is required to interpret Results of any of these calculations; two or three different methods may often be employed in order to estimate the flow characteristics of the two-phase system considered. At the same time the long time experience suggests that some empirical correlations can be quite capable of providing useful results.

Such a situation is clearly unsatisfactory. On the other hand, a theoretical model derived fron the first principles remains to be an elusive goal, because it is either impossible or impractical to solve the model equations and the relative simplicity of the empirical correlations, another approach is being considered; mechanistic modeling.

In developing these models, a particular fluid transport mechanism is assumed to prevail over a limited range of conditions. Subsequently, a set of equations describing the mechanism involved is formulated. Models of this nature involve a mixture of vigorous statements and purely empirical relations. Typically, these methods are of a composite nature requiring prediction of the flow pattern first and then using the model equations which would be applicable to the prevailing regime under the given conditions. Significantly, these models may even have the capability of predicting some of the flow characteristics. Although the mechanistic models are not available for all cases of interest at the present time, it is highly plausible that they would replace the purely empirical methods in the not too distant future.

Recently, a comprehensive model on vertical upward flow was proposed by Ansari et al.(AA)(1). It is purpose of this study to evaluate this mechanistic model and to compare its performance with five other methods currently used in petroleum industry.