Design Optimization of Plunger Lift Systems

Abstract

ABSTRACT A general dynamic plunger lift model is presented which can be used to predict optimum design of a plunger lift system for wells which are producing by any reservoir mechanism. The upstroke and downstroke plunger models are coupled to a generalized inflow performance relationship thereby matching the production capability of the reservoir to the plunger dynamics. By matching reservoir performance and plunger dynamics the optimum slug size and cycle time can be determined which will maximize the liquid production for a given well. A discussion of the development of the dynamic plunger lift model is presented and performance comparisons are made with other models available in the literature. Conclusions are stated and potential improvements addressed concerning future work in plunger lift technology. INTRODUCTION Natural plunger lift is an intermittent artificial lift technique utilizing a free piston (plunger) cycling up and down inside the tubing (or casing) of a well. Generally, no packer is set in the well or an existing packer is breached to allow gas storage space in the casing-tubing annulus. When the gas pressure in this annulus space is sufficient, the flowline at the surface is opened and the plunger with its liquid slug load begins traveling up the tubing. As the plunger arrives at the surface, the liquid slug is produced into the flowline, the flowline is closed, and the plunger falls to the bottom of the well. While the well is shut in, and the plunger is falling, the pressure in the well is building up in order to re-cycle the plunger. Plunger lift enjoys several major advantages over other artificial lift techniques, but also has some limitations. An advantage over other lift methods, such as sucker rod pumping installations, is the relatively smaller initial investment needed for plunger lift and its inexpensive operating cost. Also, the plunger practically eliminates liquid fallback which results in greater production efficiency than intermittent gas lifted wells. Finally, the plunger can remove paraffin buildup from the tubing walls with each cycle and saves the costly downtime of cleaning paraffin from the tubing walls. Two of the biggest plunger lift limitations are in wells with sand production problems and the lack of field personnel trained in plunger lift systems.