DYNAMIC MODELING OF PARTIAL LIQUID LIFT FOR STRIPPER GAS WELLS

This paper presents the results of a dynamic modeling approach for prediction of critical rate to unload stripper gas wells. Methodologies in the literature such as the ones by Turner et al, Lea et al and Coleman et al predict critical gas rates by using force balances based on bulk properties of the liquid and gas column. Using a one dimensional modeling of two phase flow in a vertical column, we are able to incorporate the phase behavioral effects caused by temperature and pressure changes affecting fluid density and localized conditions of liquid droplets demonstrating a more accurate way to predict critical gas rates.

The dynamic prediction model allows incorporation of the formation depth and pressure, temperature gradients and tubing size. Gas composition range from dry gas to rich gas with potential for condensate formation. The model allows mapping and tracking the phase behavior conditions after flow stoppage under the condition of low gas rate and the energy requirement to partially lightening the liquid column and resuming gas flow.

The wellbore simulation model is tested using data from a low pressure gas field in Texas. Energy requirement for partial fluid lift and its amenability for automation is shown to be superior for very low pressure gas wells where conventional soap injection and plunger lift are no longer practical alternatives.