ABSTRACT

The paper describes the two-phase vertical-lift function, explains the hydraulics of natural flow, outlines two-phase flow through orifices, summarizes methods for estimating individual well capabilities, and includes approximations for solution of natural flow and gas-lift problems for tubing of the 1.66-, 1.90-, 2.375-, 2.875- and 3.50-ln. API sizes, and crude oils in the gravity range from 25 to 40 API

INTRODUCTION

Advances in knowledge of the different lifting methods do not lend themselves to evaluation quickly or in simple economic terms. In the aggregate, however, they constitute the necessary basis for improved lifting policies and profitabilities, wherever oil is raised.

Production by natural flow rightly tops the list of lifting methods, inasmuch as it produces more oil than all other methods combined. It proceeds with minimum cost in relative absence of operating difficulties; and is relinquished finally in an atmosphere charged with regret, and supercharged with expletives intended to fortify the conclusion that the stoppage is an irreversible act of Providence. Nevertheless, production men have been haunted for years by the thought that a more definite knowledge of flowing performance would suggest means of resuming flow after premature stoppages, permit more effective well control, more appropriate How-string selections, and serve in general to Increase the proportion of oil quantities economically recoverable by natural flow.

Development of organized information on vertical-flow has been so far a matter of slow growth. A presentation in 1930 of the basic theory by the late Professor Doctor J. Versluys1 provided an initial impetus for current developments, but has been applied only to a limited extent because of practical difficulties in evaluating factors which appear in the Versluys differential.

An Interesting attempt to solve the problem of two-phase vertical lift testing flow through short (67-ft) tubes was reported in 1931 by T.V. Moore and H, 1). Wilde.2 Failure of this project to provide the desired generalization seems attributable to use of tube lengths so short that representative conditions were not attained. kemler and Poole,3 in a paper on flowing wells presented before the American Petroleum Institute in 1936, developed a limited correlation between gas-liquid ratio and pressure drop per unit of tubing length, and explained a method of estimating flowing life. The work of C. J. May and A. Laird4" resulted in vertical-lift generalizations well adapted to predict results within a restricted range of conditions. The interesting paper by Poettman and Carpenter6 appeared subsequent to the time of derivation of the material here presented.

"Gas-Lift Principles and Practices" by S. F. Shaw,7 the pioneer consultant on vertical flow, provides an interesting discussion of gas-lift history and methods with correlations which, though limited in scope, were none the less useful. Shaw's observation, that power functions may be applied in approximating the relationships between minimum gas-lift intake pressures and given liquid production rates, has been used here.

The excellent paper by L. C. Babsone8 added considerably to knowledge of vertical Bow, particularly in the range for gas-liquid ratios greater than 2.0 Mcf per bbl. To a large extent the present paper is a result of reviewing Babson's data and work after adding a considerable fund of depth-pressure

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