Benefits of Slow-Speed Pumping

Technology Today Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleum engineering. Abstract One of the most significant operating costs (frequently the largest) associated with sucker-rod pumping is the expense of pulling and repairing the rods, pump, and tubing. Many wells are pulled for repairs so often that they are marginally economic. This problem is made worse by the days of lost production associated with the downtime. This work demonstrates how pumping slowly can solve these difficulties, making marginal wells economic over a long period of time. Introduction As a reservoir depletes, a sucker-rod pump will be able to lift more liquid than the reservoir can deliver. Excess pumping capacity results in excessive wear from shock loads caused by fluid pound and unnecessary friction and stress fluctuations. The customary method of limiting this damage is to pump intermittently. This is done by placing the unit on a timer or by installing a pump-off controller. Both methods have at least four drawbacks.• Intermittent pumping changes the frequency, but not the pumping speed. When the unit comes back on, the loads associated with motion and fluid pound reoccur.• During the time when the pumping unit is off, the reservoir is flowing liquid into the wellbore. This flow builds a liquid level in the casing, which creates backpressure on the producing formation. Maximum flow occurs with minimum backpressure, which is achieved by keeping the column of liquid in the casing as small as possible.• Starting the unit from a dead stop requires the maximum power usage. The start phase also is a significant shock on the pumping unit, rods, and pump.• If the well produces any solids, the downtime allows the solids to settle. These settled solids will increase the frequency of stuck plungers. Therefore, customary methods cannot eliminate all the shocks, unnecessary pump cycles, and unnecessary power use, nor can they provide the minimum backpressure against the reservoir at all times.