An Analytical Concept of the Static and Dynamic Parameters Of Intermittent Gas Lift

Abstract

An analytical method for describing the events of pressure , velocity and liquid fall-back in relation to time and other well variables from initial injection to completion of an intermittent gas-lift cycle is presented herein. Development of the method proceeded from mathematical postulates verified first by the construction of an electronically instrumented model, using the principles of dynamic sim-ilm'ity, and later by actual field data. Application of the method to intermittent gas-lift installation design is achieved by organizing well parameters into dimensionless ratios and applying the mathematical system to describe the results of gas injection. The method permits definition of optimum values of pressure, submer-gence, injection rate and volume, slug velocity, depth of injection, point of cutoff , production per cycle and gas-liquid ratio for a particular well setting and set of formation characteristics. To obtain this definition, the production of a slug of fluid has been divided into three successive intervals. Three systems of differential equations, each continuous over one of the intervals, were derived and subjected to verification. The discovery of a natural constant in the gas-liquid system has resulted in major simplification of the mathematical system for design work. Correlative data are presented from past recorded installations as well as from current field tests.