Abstract

The production of oil wells on intermittent gas lift can be increased by properly selecting the optimum cycle time and injecting the correct amount of gas at the required injection pressure in each cycle. Due to the complexity of the process, some times the production engineer is forced to perform downhole pressure surveys to have a better understanding of the well performance and therefore, improve the quality of the trouble shooting outcome. This kind of procedure is specially important for choke control intermittent gas lift where a precise knowledge of the inflow and outflow behavior of the well is needed.

In this paper, a detailed description of the correct procedure for performing and analyzing a downhole pressure survey is given. The survey procedure is a combination of static and dynamic downhole surveys which when properly done and analyzed, will provide the following information:

  • optimum cycle time;

  • productivity index;

  • current fallback;

  • real fluid gradient;

  • static reservoir pressure and other reservoir properties.

The mathematical procedure used to find the liquid slug length as a function of time and the productivity index is derived in the paper and a computer algorithm to perform these tasks is presented. Actual downhole measurements closely match the computer output.

A 30% increase in production was obtained when the procedure presented in this paper was applied to 10 wells in Lake Maracaibo Gas Lift Field. The surveys outcome and the necessary adjustments are also presented in the paper.

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