Plunger Lift Optimization by Monitoring and Analyzing Wellbore Acoustic Signals and Tubing and Casing Pressures

Abstract

Abstract Plunger Lift operations are oftentimes not optimized due to lack of knowledge of plunger location and changes in tubing pressures, casing pressures and bottomhole pressures. Monitoring the plunger location in the tubing helps the operator to optimize the production of liquid and gas from the well. In low liquid volume wells, the plunger position can be tracked from the surface by monitoring acoustic signals generated as the plunger falls down the tubing. When the plunger falls through a tubing collar recess, an acoustic pulse is generated. These acoustic pulses, generated at the tubing collar recesses, travel through the gas in the tubing and can be monitored at the surface to obtain plunger depth. These acoustic pulses are converted to an electrical signal by use of a microphone or pressure transducer. The signal is digitized, stored and processed in a computer to determine plunger depth. In some high liquid volume wells, the acoustic pulses generated as the plunger falls past the tubing collar recesses may be masked and not detectable due to liquid accumulation around the plunger. However, in both low and high liquid volume wells, the plunger depth can be determined by generating an acoustic pulse in the tubing at the surface, and monitoring the acoustic reflection from the top of the plunger. Multiple shots are taken, so the plunger descent rate can be determined throughout the plunger fall. Software processes this plunger depth 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 data plots. Well inflow performance is calculated and plotted. Software displays the data and analysis in several formats including a pictorial representation of the well showing the tubing and casing pressures, plunger location, gas and liquid flow rates in the tubing and annulus, and inflow performance relationship at operator selected intervals throughout the cycle. A field case is presented to show how this field data analysis is applied to optimization of Plunger Lift operations. Introduction Plunger lift is a low cost method for lifting liquids (water, condensate and/or oil) from gas and oil wells. The plunger lift system reduces the cost of operating a well compared to other artificial lift methods, because the formation pressure supplies the energy required to lift the liquids. During plunger lift operations the motor controlled valve is opened and at a later time shut-in. During shut-in the gas flow down the flowline is stopped when the surface valve is closed, allowing the plunger to fall down to the bottom of the tubing. After a pre-determined amount of time elapses the surface flow valve opens and the tubing pressure begins to drop toward the low flowline pressure. The differential force across the plunger, due to the drop in pressure in the tubing above the liquid column and the high well pressure below the plunger, lifts the plunger and a portion of the liquid above the plunger to the surface. The open and shut-in operational cycle of the plunger lift system is repeated throughout the day to produce liquids and gas from the well. In plunger lift wells, acoustic fluid level instruments can be used to passively record the acoustic signal produced as the plunger falls down the tubing and to monitor the variation of pressures during the plunger cycles. The objective of the operator is to acquire acoustic and pressure data and to process the information to determine the 1) depth to the plunger 2) fall velocity of the plunger 3) time for the plunger to fall to the liquid 4) time for the plunger to fall to the bottom of the tubing 5) the volume and rate of gas flowing into the well 6) the appropriate cycle times for optimum operation. While at the well as the collected data is analyzed, the goal for the plunger lift analyst should be to answer the WELL PERFORMANCE QUESTIONS listed in Table 1. The well can be more efficiently produced if the well performance questions are answered. Analysis of the collected data is used to optimize the operation of plunger lifted wells. The following sections of this paper describe the procedure used to acquire the data for plunger lift analysis. Example data showing various operational problems encountered during operation off plunger lift systems will be presented.