Abstract
Rosa Mediano is the field with the lowest reservoir pressure in Lake Maracaibo. For this reason, a large number of wells are currently producing on choke controlled intermittent gas lift. The objective of this work was to identify operating conditions that could be modified in order to optimize gas consumption and maximize liquid production.
To carry out this objective, more than 50 down-hole pressure and temperature surveys were run in a total of 7 oil reservoirs. The survey procedure was such that an important number of engineering parameters could be obtained: real liquid pressure gradient, optimum cycle time, liquid fallback and the productivity index of the well.
Important deviations of the dynamic behavior of spring loaded and nitrogen charged gas lift pilot valves were identified and they are presented in this work. The analysis of down-hole pressure surveys also shows that, in many cases, the liquid fallback was well above the usually assumed 5% of the initial liquid column length per thousand feet traveled. These measurements are presented in the paper, together with a discussion of possible causes.
The proper gas injection pressures, gas volume injected per cycle and optimum cycle times were calculated from the reservoir inflow capabilities. An overall 30% increase in liquid production was obtained when these parameters were adjusted to new values calculated from the survey analysis. A shift from choke control to the use of surface controllers was necessary in some cases and detailed examples are presented in the paper.
Finally, the analysis of down-hole pressure surveys performed on 6 double packer Gas Lift Chambers shows that this type of completion is highly inefficient for wells with moderate to high formation gas-liquid ratios.
