Gas lift has become the favored artificial lift method for unconventional wells in the Permian Basin. It provides reasonable tolerance to gas production and surging trends while maintaining flexibility for an unconventional well’s rapid production decline. These wells are produced from a fixed stimulated reservoir volume (SRV) where the fractures created close and affect production.
The SRV often maintains gas and water inflow that result in near flow conditions throughout the economic life of the well, so current directives to shrink costs lead many designers to reduce the number of unloading valves in a gas lift design. While this concept is valid, rapidly advancing technology can stretch the limits of well spacing, proppants, chemicals, parent-child relationships and, unfortunately, frac hits and wellbore damage that affect near flow conditions and compromises production.
A conservative approach to gas lift design is the design line method, based on a projection of inflow conditions in later stages of the well. This design can continue to produce the well when the unexpected occurs and/or throughout the life of the well.
The Design Line method includes Nodal analysis of flowing conditions along with established engineering relationships while using a time-tested method to predict inflow as SRV pressure declines. The result may be to add one or two more unloading valves, using an algorithm to locate valves to bottom. This design should meet the well’s future needs, which may eventually require plunger lift assistance.