Abstract

Accurate prediction of multi-phase flow through chokes is required for modern production design and optimization of oil well performance. Most of the Middle-East oil wells are uniquely characterized with high production rates. Several correlations that relate the choke size with other variables involved in the multi-phase flow phenomena have been proposed in the literature. The validity of these correlations for Middle-East oil wells has been assessed in this study.

A new correlation has been developed to describe the choke performance of the Middle-East oil wells. The proposed correlation is similar to the Omana-type correlations based on dimensional analysis. This correlation was examined against a wide range of well test data collected from various oilfields in Egypt, Kuwait, Libya, and other Middle-East countries. Statistical analysis was used to compare to accuracy of the results obtained from the new correlation with those from other correlations. The effect of different PVT correlations on the predictive accuracy of the fluid flow equations has been also investigated. These properties included the surface tension of the gas/oil system, gas compressibility factor, solution GOR, and oil volume factor.

The developed correlation provided highly accurate results compared to the other existing correlations. This correlation is applicable for critical flow conditions and requires knowledge of the PVT data. This study showed that the use of different PVT correlations resulted in slight variation in the accuracy of the developed correlation.

Further analysis has been conducted in the present study on the Gilbert-type empirical correlations. Results emphasized the linear relationship between flowrate and upstream pressure for critical flow.

Introduction

The choke is an important element in the well production system. One of the main functions of choke is to control flow. The pressure drop is an important factor influencing the pressurization of the formation and as a result the performance and productivity of the well. A choke malfunctioning may cause the downstream pressure disturbances to be transmitted upstream leading to damage of surface facilities or death of oil well. Therefore, the prediction of flow behavior of multi-phase mixtures through chokes is of great industrial interest in the design and development of producing wells. Furthermore, modern techniques are currently used in the design and optimization analysis over the entire production system. This analysis requires accurate models that can describe the performance of each component in the system; including the wellhead choke. Several models of multi-phase flow through chokes exist in the literature. Most of these models were developed for limited ranges of production conditions. The magnitude of production rates of the flowing oil wells in the Middle-East countries is unique. Therefore, more research is needed to justify the validity of the available models for Middle-East oilwells.

Literature Review

Two-phase low through chokes may be either critical or subcritical. Most of the models presented in the literature were developed for critical flow. These models comprise the Gilbert-type1 empirical relationship. This relationship was revised by Ros, 2 Baxendell,3 Achong,4 Pilehvari,5 Secen, 6 and Osman andDokla.7 These correlations consist basically of a three-parameter equation in which the flow rate is linearly proportional to the upstream pressure.

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