Abstract

Development of a new portable monitoring system has taken the guesswork out of plunger lift analysis, troubleshooting and optimization. During one or more plunger lift cycles at high sampling speeds this system acquires data from the tubing acoustic signals plus pressure recordings from both the tubing and casing. The plunger generates an acoustic pulse as it falls through each tubing collar recess when the well is shut-in. Each acoustic pulse travels through the gas in the tubing and is detected at the surface. The pulses are converted to an electrical signal by a microphone and pressure transducer. The signals are digitized, stored and processed in a computer to determine plunger position, plunger fall velocity, and plunger arrival at the liquid level in the tubing. By analyzing the collected data the operator can ensure that the plunger reaches the bottom of the tubing before the end of the shut-in time period. Setting the well's controller to have the shortest possible shut-in time period can maximize oil and gas production from the plunger lift installation. Example data collected from various plunger lifted wells are presented in this paper to show how to identify operational problems such as holes in the tubing, stuck plungers and plungers not getting to bottom.

The problem of not knowing the plunger location during the operation cycle has been overcome with this new technology by allowing the operator to see the plunger location at any time during the cycle. Having a detailed analysis of the operation of the well makes optimization of plunger lift production achievable with a minimum of effort and avoids the usual waste of time due to trial and error procedures. Knowing the plunger's location is equally important for timer-based as well as intelligent controllers, since in both cases it is necessary to make initial estimates of the appropriate shut-in time, plunger arrival time and plunger fall time. The capability to calculate the volumes of liquid and gas produced during the cycle and determining the well's inflow performance gives valuable information to determine the opportunity for increased production. Determining the position and velocity of the plunger throughout the cycle can aid in maximizing oil and gas production of a plunger lift installation.

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.

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