Plunger lift and compression are two common methods of dealing with liquid loading issues in natural gas wells. However, as the average productivity of the gas wells in the Western Canadian Sedimentary Basin continues to decline, these methods on their own are no longer sufficient for many wells. However, plunger lift combined with compression, using newly-developed and innovative tools and techniques, can provide a solution for many low-rate wells that could not otherwise be produced cost-effectively.
The maturing of the Western Canadian Sedimentary Basin and the decline in the average natural gas well production rates, combined with the current and forecasted strong demand and high commodity prices for natural gas, has led to a need to find ways to produce gas wells down to lower and lower rates before they are shut in and abandoned. As a result, tools and techniques to deliquify these types of gas wells have become increasingly important over time, and will continue to grow in importance over the near and long term future.
Both plunger lift and compression are tools that have been used to help deliquify gas wells for many years. Although there are a number of synergistic effects that occur when plunger lift and compression are combined, there are also a number of operational issues that make it somewhat challenging to bring the two technologies together.
In order to have a better understanding of the tools, techniques, and advantages involved in combining compression and plunger lift to deliquify low-rate gas wells, it is necessary to understand i) how liquid loading occurs and how it impacts well productivity, ii) how plunger lift is used to help deliquify low-rate gas wells, iii) how compression is used to deliquify low-rate gas wells, iv) the synergistic effects of combining plunger lift and compression, v) the operational challenges that arise when combining plunger lift and compression; and vi) the tools and technologies that can be applied, or are being developed, to enable compression and plunger lift to be combined in a cost-effective manner.
According to Lea et al, "liquid loading of a gas well is the inability of the produced gas to remove the produced liquids from the wellbore".i The point at which liquid loading will begin to occur in a producing well can be estimated by calculating what is known as the critical gas velocity which, for any given set of conditions, can be translated into a critical rate, i.e. the gas production rate below which the produced gas will no longer be able to lift the produced liquids. There are a variety of methods available to estimate the critical rate, but the most important variables in determining the critical rate are those that determine the velocity of the gas, i.e.
the gas production rate,
the inner diameter of the tubulars through which the gas is flowing,
the pressure at which the gas is flowing; and
the temperature of the gas.
