Real Gas Lift Optimization: An Alternative to Timer Based Intermittent Gas Lift

Abstract

A simple electronic control method for automatically determining the "on-time" parameter for intermittent gas lifted wells using existing continuous gas lift valves is presented. Lift gas consumption and production during intermittent operation is compared to previous continuous gas lift results of the same wells in an unconventional reservoir. Performance during abnormal field conditions is analyzed. Interpretation of pressure/flow curves is explained.

Algorithms in electronic controllers normally used for plunger lift optimization are adapted to intermittent gas lift. Several pressure and flow phenomenon indicate the stage of the intermittent gas lift cycle. The most important indicator is a sudden increase in tubing pressure and gas production rate which signifies the arrival of fluid at the surface of the well. A setpoint is used to determine that the fluid slug has arrived and the gas injection is then brought to a halt until a timer or other parameter determines the beginning of the next injection cycle.

Nearly all wells which were tested with the new control algorithm showed a large drop in consumption of lift gas, which was the only target of the test. The wells which showed the greatest lift efficiency improvements produced on average less than 150 barrels of total fluid per day. Many wells may have been producing less fluid under continuous gas lift due to higher average bottomhole pressure under continuous injection conditions. Nearly all wells maintained or increased production after the change. The use of an automatic on-time adjustment maintained production under scenarios where strict timer-based systems would have failed to produce fluid. The amount of time needed to restart a well after an automatic shut-in was reduced by closing the gas lift injection valve when a flow obstruction was indicated by rising tubing pressure and automatically restarting the well when conditions improved.

This method is a simplified control strategy which can be implemented and maintained with little user intervention. Practicing engineers responsible for optimizing large groups of wells may find value in this novel strategy. The shale operator received a ROI of 7 days using this new approach.