Plunger Lift operations are difficult to optimize due to lack of knowledge of tubing pressure, casing pressure, bottomhole pressure, liquid accumulation in the tubing and location of the plunger. Monitoring the plunger position in the tubing helps the operator (or controller) to optimize the removal of liquids and gas from the well. The plunger position can be tracked from the surface by monitoring acoustic signals generated as the plunger falls down the tubing. When the plunger passes by a tubing collar recess, an acoustic pulse is generated that travels up the gas within the tubing. The acoustic pulses are monitored at the surface, and are converted to an electrical signal by a microphone. The signal is digitized, and the digitized data is stored in a computer. Software processes this data along with the tubing and casing pressure data to display plunger depth, plunger velocity and well pressures vs. time. Plunger arrival at the liquid level in the tubing and plunger arrival at the bottom of the tubing are identified on the time plots. Inflow performance is calculated. Software displays the data and analysis in several formats including a graphical representation of the well showing the tubing and casing pressures, plunger location, gas and liquid volumes and flow rates in the tubing and annulus, and inflow performance relationship at operator selected periodic intervals throughout the cycle. A field case is presented to show how this information is applied to optimization of Plunger Lift operations.
Plunger-lift has become more popular in recent years due to better mechanical equipment, improved electronic controllers and a better understanding of the operating system1–13.
A plunger-lift data acquisition and analysis system has not been available so that the performance of the plunger-lift system can be fully analyzed and understood. This paper describes a new portable data acquisition system that allows the operator to analyze a plunger-lift system, and then, improve the well's production by optimizing the shut-in and flow times and other operational parameters that are associated with the plunger-lift system.
A feature of the plunger-lift artificial lift system is that the reservoir gas energy is used to lift the liquids to the surface without addition of external power. Thus, plunger-lift systems are less expensive to operate and install than most other artificial lift systems. However, a limitation of plunger-lift is that sufficient energy in the form of compressed gas from the reservoir must be available in the wellbore to lift the produced liquid to the surface. Also, the producing bottomhole pressure must be sufficient to lift the produced liquids from the reservoir to the surface and also overcome surface pressure.
Please refer to Figure 1 for a schematic of a typical plunger-lift system. The plunger-lift operation is separated into 3 stages, namely, the Unloading, the Afterflow and the Shut-in. In this paper, data is analyzed during a complete cycle, which includes the Unloading, Afterflow and Shut-in periods. The beginning of the analysis cycle is the beginning of the Unloading period, and the analysis continues through the end of the Shut-in period. Following is a discussion of a normally operating plunger-lift system.