Successful Application Of Pump-Off Controllers
Authors: Westerman G. Wayne 
Published: December 2007

One of the major sources of problems associated with rod pumping is pump-off and the associated fluid pound. After several pumping is pump-off and the associated fluid pound. After several years or development, techniques and systems are available to reliably detect and control pump-off. Extensive evaluation and operational experience have established economic benefits and the requirement for modification of operation and management systems.

Introduction

Rod pumping is one of the oldest and by far the most common artificial lift method used in oil production. As in any mechanical system, there are both advantages and disadvantages to the use of rod pumping systems. The relative simplicity, dependability and serviceability of the system by and large outweigh its disadvantages.

One of the generally accepted operating compromises of a rod pumping system is providing lift capacity in excess of the production. The result of over displacement is operating the production. The result of over displacement is operating the subsurface pump in an inefficient, partially filled or "pumped off" condition. The fluid pound associated with pump off is responsible for damage to the rod string, pump, and, in some cases surface equipment.

Over the past several years, there has been an ongoing effort to develop techniques and equipment for the detection and control of pump off. The development of a generally applicable pump off control method was complicated by pumping abnormalities pump off control method was complicated by pumping abnormalities not associated with pump off such as gas interference, harmonic pumping speeds, down hole friction, equipment vibration, corrosion, pumping speeds, down hole friction, equipment vibration, corrosion, etc.

The application of pump off control is also complicated by a lack of a thorough understanding of the operation of a rod pumping system and its relation to the reservoir. While significant progress has been made in the development of the techniques, progress has been made in the development of the techniques, application criteria and economic justification for the implementation of pump off control, much additional effort is required in order to assure the maximum expectation of this relatively new technology.

In an era of decreasing supply and increasing demand for energy, the proper execution of pump off control holds a great potential for reduced operating cost and improved profits. potential for reduced operating cost and improved profits. Pump off control offers a means for improving profitability through reduced energy consumption, reduced maintenance cost, and improved operating efficiency.

A BRIEF HISTORY OF PUMP OFF CONTROL

Almost since the beginning of commercial oil production, rod pumping has been an important part of the production process. pumping has been an important part of the production process. Although the rod pumping operation is basically simple, it is greatly complicated by the effects of the stretch in long rod strings, the dynamics of the pumping unit and rod string, productive rate of the reservoir, etc. productive rate of the reservoir, etc. One of the problems to be recognized early in the history of rod pumping was the difficulty of exactly matching the pumping systems capacity to the productivity rate of the reservoir. In order to obtain maximum production from a well, it is generally necessary to maintain the lowest possible fluid level and, therefore, lowest possible back pressure on the formation. in order to assure a low possible back pressure on the formation. in order to assure a low average fluid level, it is necessary to provide a pumping system capacity in excess of the productivity capacity of the well. The excess pumping capacity required to maintain a low fluid level insures pump off.

The first effort that was made to deal with the pump off problem was to manually start and stop the operation of the problem was to manually start and stop the operation of the pumping system. This approach requires the lease operator to pumping system. This approach requires the lease operator to estimate the amount of pumping time required to obtain the production from the well and to manually control the well to production from the well and to manually control the well to provide that amount of pumping time. The disadvantages of this provide that amount of pumping time. The disadvantages of this kind of operation are obvious.

The first attempt to automatically control the operation of the pumping system was to install time clocks which automatically start and stop the operation of the pumping system. The earliest version of these time clocks provided control operations at one hour intervals. Later versions of time clocks offer 15 minute intervals. in time clock operations, the operator is called on to make the decision as to the amount and the distribution of the pumping time required to obtain the production from a given well. pumping time required to obtain the production from a given well. Human nature being what it is, along with the work loads of operators (pumpers), the time cycling operation is almost guaranteed to provide either over or under displacement. provide either over or under displacement. In recognition of the problems associated with the use of time clocks, the percentage timer was developed.