Abstract

Liquid loading is an important determinant for the performance of tight, unconventional gas wells. Although plunger lift is one of the best solutions when applicable, marginal economics of unconventional gas production does not tolerate un-optimized plunger lift performance. In this paper a reservoir-performance based algorithm proposed by Ozkan et al. (2003) is applied to optimize the gas production and shut-in periods of plunger lift operation. The objective of the optimization is to maximize gas production with the condition that the liquid loaded during production can be lifted to the surface by the pressure that builds up during the following shut-in period. Unlike the current plunger lifts that work in time mode (like timer clock), this algorithm is based on pressure (pressure mode). The optimization algorithm combines the conventional plunger-lift theory with an analytical description of the reservoir performance. The conventional plunger lift theory provides the pressure required for lifting the plunger with a liquid column on top of it, and the analytical reservoir model is used to optimize the sequence of production and shut-in times. The optimization algorithm presented in this paper improves the economics of unconventional gas production not only by increasing gas production but also automating the process by which optimization is achieved. Another advantage of the proposed method is the ability to automatically adjust to changes in the line pressure. A case study is presented to demonstrate that the proposed automated model can achieve the same optimization performance as that implemented by expert technicians.

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