The Sucker-rod Pump as a Problem in Elasticity
- John F. Kendrick (Sullivan Machinery Co.) | Paul D. Cornelius (Sullivan Machinery Co.)
- Document ID
- Society of Petroleum Engineers
- Transactions of the AIME
- Publication Date
- December 1937
- Document Type
- Journal Paper
- 15 - 31
- 1937. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 3.1.1 Beam and related pumping techniques, 4.3.4 Scale, 2.4.3 Sand/Solids Control
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This paper is a progress report of a study the authors are making of thesucker-rod pump, considered as a vibrating system with one degree of freedom,with forced vibrations and with viscous damping. Dr. S. Timoshenko's formula isgiven, defining such a system. Each factor is considered in respect to theproblem of operating sucker rods, and the zone is pointed out in which themathematics do not apply to the sucker-rod pump, because of its variable mass.This general theory is interpreted in the light of nearly two years of testingwells in the field, and correlating the results of other tests.
The motion of the pumping mechanism is a vibration. The string of sucker rodsvibrates with a natural frequency. The motion of the plunger is the result ofadding together these two vibrations, and is modified by a damping or frictionfactor. The controlling factor appears to be the ratio of the period of thenatural vibration of the rod string to the period of the vibration of the pump.The first conclusion is that a definite value of this ratio, which is belowresonance and is probably not greater than 0.5, should not be exceeded in orderto assure satisfactory performance from the sucker rods. The second conclusionis that the component parts of the pumping equipment should be selected to givethe smallest practical period of the natural vibration, and when this does notpermit operation at a safe speed and give the required plunger displacement, alonger polished-rod stroke should be used.
While the quantitative results are but rough approximations, the qualitativeanalysis of pumping problems on this basis promises to be of considerable valuein diagnosing the cause of poor performance and prescribing suitableremedies.
The trouble that results, whenever it becomes necessary to crowd the sucker-rodpump, to take potentials or to handle increasing volumes of water, isresponsible for the belief that this type of pump is not equal to present dayneeds, and that it is only a question of time before some other pumping devicewill take its place.
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