Abstract

Throughout the world the most commonly used method to artificially produce wells is by sucker rod lift. Low producing efficiency caused by incomplete pump fillage is the most common operational problem experienced by sucker rod lifted wells. Incomplete pump fillage is the result of having a pump capacity that exceeds the production rate of the well or having poor gas separation at the pump intake with a portion of the pump displacement being lost to gas interference. More efficient operations and lower cost will result, if these wells are operated with the pump filled with liquid by eliminating any gas interference in the pump and controlling pump run time so the pump displacement will match the inflow of liquid from the reservoir into the wellbore. The operator must monitor well to insure that the pump has no mechanical problems and efficient operations are maintained as all the available liquid is produced from the wellbore.

Introduction

Sucker rod lift systems are the most common method used to artificially produce oil wells. Inefficient energy use is one of the most common operational problems experienced from these the sucker rod lifted wells. Due to the inefficiencies of the various components of the sucker rod lift system1 energy losses occur in lifting the liquid to the surface. The pump being incompletely filled with liquid is the most common reason for low producing efficiencies and usually the largest source of energy waste. More efficient operations and lower power use will result, if these wells are operated with a pump filled with liquid. The first step in this process is to eliminate any gas interference in the pump and insure that the pump has no mechanical problems; then the next step is to optimize the pump displacement to remove all the available liquid from the wellbore. To match the pump capacity to the production potential of the well some simple changes in pumping speed and stroke length can be made. Controlling the pump run time with a pump-off controller or a percentage timer can adjust the number of strokes so that the pump displacement will equal the volume of liquid that flows into well bore. Operating the pumping system with a pump barrel full of liquid will result in more efficient operations and lower power use.

Wells that operate 24 hours per day and have a pump capacity in excess of the well's producing rate "pound" liquid on the down stroke. This "pounding" of the pump plunger against the liquid causes shock loading throughout the entire pumping system. The shock loading can cause rod buckling, pump wear, tubing wear, severe rod loading changes, and pumping unit vibration even to the extent that the vibration can be visually observed and heard. Changes in loading are easily measured using a dynamometer system. Sudden changes in rod loading on the downstroke also affect the pumping unit balance and motor power requirements. Longer life will be experienced by the pump, rods, tubing and pumping unit system if the plunger does not "pound" liquid near the middle of the down stroke. Operating the pumping system with a pump barrel full of liquid will result in longer equipment life.

Analyzing the performance of the pumping system requires an integrated analysis2 of the prime mover, surface equipment, wellbore equipment, down hole pump, down hole gas separator, and the reservoir. One of the cost-effective advantages of an integrated analysis system is that the well data is entered only once and all of the calculations use the data to determine the complete system's performance. The analysis is based on information obtained from liquid level instruments, dynamometers, and motor power probes. Use of a portable system at the well site allows immediate analysis of any operational conditions that may be hindering the performance of both the equipment and the well. The operator using the integrated analysis method can identify the cause of any operational problem, monitor pump conditions, and optimize withdrawal rates, thereby efficiently producing the sucker rod lift well.

Performing an acoustic producing level survey, dynamometer survey, and power survey begins the process to determine the producing efficiency of lifting the liquid to the surface. The energy efficiency of lifting the liquid to the surface plus a pump dynamometer card indicating percent pump fillage provides the information necessary to optimize the operation of the sucker rod lift system. This paper discusses how to maintain a high producing efficiency in sucker rod lift operations.

This content is only available via PDF.
You can access this article if you purchase or spend a download.