Resolving discrepancies in predicting critical rates in low pressure stripper gas wells

The minimum gas rate for unloading liquids from a gas well has been the subject of much interest, especially in old gas producing fields with declining reservoir pressures. For low-pressure stripper gas wells, liquid production accumulating in the tubing is a pivotal factor that could lead to premature well abandonment and a huge detrimental difference in the economic viability of the well.

Some notable correlations that exist for predicting the critical rate required for liquid unloading in gas wells include Turner et al., (1969), Coleman et al., (1991), Nosseir et al. (1997), Li et al. (2001) and Veeken et al., (2003). However, these correlations offer divergent views on the critical rates needed for liquid unloading, and for some correlations in particular, at low wellhead pressures below 50 psia.

The objectives of this research are to evaluate discrepancies in the previous work on critical gas velocities required to keep liquid from accumulating in the tubing. Also during the course of the work, data were collected using a flow test facility at Texas Tech University. The critical gas rates were experimentally measured in order to determine an improved correlation with specific application for low-pressure stripper gas wells below 50 psia and at average temperature of 64 oF.