A new portable monitoring system has taken the guesswork out of plunger lift analysis, troubleshooting and optimization. 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. 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. 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.
Plunger lift is a low cost method for lifting liquids (water, condensate and/or oil) from primarily liquid loaded gas wells and is used infrequently to produce oil wells. The operating cost of plunger lift system is low compared to other artificial lift methods, because the reservoir 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 time to elapse for the plunger to fall down to the bottom of the tubing. After a pre-determined amount of time elapses the controller commands the motor flow valve to open and the tubing pressure begins to drop toward the flowline pressure. Differential force acting on the plunger results from the drop in surface tubing pressure and the high reservoir pressure below the plunger. The differential force 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.
Without acquiring a fluid level shot in plunger lift wells, an acoustic fluid level instrument can be used to continuously record at a fast sampling rate the acoustic signal produced as the plunger travels up and down the tubing and to monitor the variation of pressures during the plunger cycles. The acquired acoustic and pressure data can be processed 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.
