The design of continuous gas-lift installations has been examined in detail. Procedures are outlined showing how system analysis can be used to select optional components including tubing size, flowline size, surface operating pressure, perforation shot density. etc. An improved pressure, perforation shot density. etc. An improved procedure is presented for the construction of the gas-lift procedure is presented for the construction of the gas-lift performance curve, based on the gas injection rate rather than the performance curve, based on the gas injection rate rather than the GLR. Also, the importance of using the actual gas-lift valve performance relationship rather than the Thornhill Craver performance relationship rather than the Thornhill Craver choke equation is addressed. It is shown that utilization of the Thornhill Craver choke equation can result in serious design errors. The two most commonly used unloading design procedures are examined with modifications and improvements being recommended. Finally, it is shown how software for the personal computer can be used to readily implement these ideas.

Introduction

The objectives of this paper are to clarify the procedures used to design continuous gas-lift installations, describe how system analysis should be applied to the design and optimization of continuous gas-lift installation, and illustrate how recent advancements in software for the personal computer can help. System analysis is a procedure use to analyze the influence of individual production components such as tubing size, flowline size, separator production components such as tubing size, flowline size, separator and injection pressures., and well capacity on the entire system in order to optimize an individual well or a group of wells. System analysis was firs describe by W. Gilbert some 26 years ago for continuous flowing wells. This technique was later perfected by Nind, Brown and others. Their procedure used gradient curves and others. Their procedure used gradient curves and other empirical correlations for the two-phase pressure drop so that the hand calculated analysis could be performed. Recently, this process has been computerized and today most producing companies have some sort of system analysis program and are using it on a daily basis to optimize existing production facilities, or to design new ones. Using this technique has been shown to be extremely beneficial.

In 1981, Brown et al. presented an article extending the system analysis technique to the optimization of continuous gas-lift installations. The system graphs were generated using a Johnston Macco Schlumberger mainframe computer program. However, the paper fails to address gas-lift valve spacing and the effect of gas-lift performance on the overall performance of a continuous gas-lift performance on the overall performance of a continuous gas-lift system. The main reason for avoiding the role of a gas-lift valve at that time was that gas-life valve performance data were available only on a limited basis. Only Teledyne Merla had been testing their valves and providing their users with the valve performance curves. The remaining valve manufacturers had been performance curves. The remaining valve manufacturers had been relying on the Thornhill Craver choke equation or modification thereof, to predict the gas passage through their valves. As will be shown later, this technique can lead to large errors (overpredicting gas passage by as much as 400%). The only reason this sad state was tolerated can be attributed to the very fact that the operator knew less about their well performance than the manufacturers knew about their equipment performance. However, looking back in time, the compression costs were low (twenty years ago, a kwh cost only 0.006) and energy costs were typically not even considered. Today as energy costs have increased more than tenfold (to more than and 0.07/kwh), the producer must pay closer attention to production costs every way to optimize his production.

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