Effect of the gas injection angle and configuration in the efficiency of gas lift

Abstract

In oil wells using gas lift as a method of artificial lift, the gas is normally injected inside the tubing at a downward direction, i.e., in countercurrent flow relative to the fluids coming from the reservoir. This creates turbulence in the flow, causing pressure drop for the gas to change direction and to flow upward along with the produced fluid. The optimization of this geometry, by changing the gas injection angle, for instance, may introduce some gain. In this paper, we present theoretical analyzes and computer simulation showing that, for high gas injection flow rates and/or small jet diameters, it is possible to obtain a gain when reversing the direction of the gas injection. Although it is intuitive that an upward injection can improve the flow, experiments are needed to give confidence to this proposal. However, there is very few studies in the literature addressing this issue. To improve the knowledge of subject, this study shows experiments performed using an experimental well flowing oil and natural gas. Such an experiment, at real scale configurations and fluids is unique. The usual configuration, injecting downward, was compared with two alternatives, injecting the gas jet upward and injecting in an annular pattern. This article describes and discusses the tests and the results obtained. Although the tests have not been performed with the ideal conditions to maximize the gain, the results were consistent and conclusive. A slight local gain was observed due to the gas angle change, consistent with the previsions of a simple theoretical model. The estimated gains can reach 2 bar and are obtained at no additional cost by simply inverting the gas jet direction, but it is more effective for wells with high gas injection flow rate. Since gas lift is applied to a large number of wells, even a modest gain can be significant in the overall context. Based on the results, it is speculated that there is probably an optimum way to inject gas by taking advantage of the jet inversion and of the reduction on slippage between gas and liquid.