Abstract

The published nitrogen temperature correction factors (Ct) are used to calculate the change in bellows-charge pressure with temperature. If these Ct-factors are used to calculate the test rack opening pressures for the gas lift valves in a high operating injection gas pressure system, the error in the temperature correction may prevent successful gas lift operations. An accurate correlation for calculating the changes in nitrogen pressure with temperature is presented in this paper. presented in this paper

Introduction

The bellows-charged gas-lift valve was invented in 1940 by W. R. King but the patent was not issued until 1944. At the time that the bellows-charged unbalanced King gas lift valve entered the market, typical operating injection gas pressures ranged from 400 to 650 psig with 800 psig being pressures ranged from 400 to 650 psig with 800 psig being an extremely high operating pressure for a closed rotative gas lift system. The advent of multiphase flow correlations for predicting flowing production pressures at depth had a major effect on the selection of increased operating injection gas pressures for deeper wells. As the accuracy of the newer multiphase correlations improved, the compressor in the dosed rotative gas lift systems were designed for higher and higher discharge pressures. Operators found that if a well could be gas lifted from near total depth, less injection gas was required to lift the well; but deeper lift required higher surface injection gas pressures.

The dosing force for most gas-lift valves is a gas charge in the dome acting over the effective area of the bellows. A schematic drawing of a typical bellows-charged unbalanced type of gas lift valve in a ring tester is illustrated in Fig. 1. The gas used in the dome of these valves is nitrogen. There are several very good reasons for using nitrogen rather than some other gas. The compressibility factors for nitrogen at high pressures and temperatures are published. Nitrogen has other desirable characteristics published. Nitrogen has other desirable characteristics such as being safe, non-corrosive, inexpensive and able in nearly all parts of the world.

Background

Since the operating pressure of a nitrogen-charged gas-lift valve changes with temperature, charts were developed for determining the change in nitrogen gas pressure for different well temperatures. One of the first charts for determining the nitrogen bellows-charge pressure in a gas lift valve at well temperature greater than the test rack base temperature of 60 degrees F was published by C. V. Kirkpatrick. The curves on this chart were based on the compressibility factors for nitrogen from API Research Project 37 Monographs.

The introduction of gas lift installation design programs by several gas lift equipment manufacturers began around 1960. Equations rather than charts were needed for the programs. programs. P. 415

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