Abstract

This paper presents salient results from a multiparticipant project conductedby AOSTRA, ARC and industry to improve rod pumping efficiency for thermal andnon-thermal oil fields in Alberta. It describes:

  • experimental and theoretical investigations on the hydrodynamics of rodpump valves that resulted in improved valve design and increased fieldproduction rates; and

  • two of the most frequent problems encountered in the field are associatedwith sand and gas/steam inflow.

These problems were examined in the laboratory (ARC) by testing ball-valvehydrodynamics at different GOR and inclination angles. Nineteen different valvedesigns currently used in Alberta were investigated using two laboratoryfacilities. Visual observations regarding critical COR and inclination anglesand quantitative measurements of pressure drop at different pump rates andfluid viscosity Here obtained. A diagram in which a generalized over-all dragcoefficient was plotted versus Reynolds number was used to capture the steadyand unsteady behaviours of the cage-ball systems; this diagram provides a basisfor improving valve design. Following discussions of the laboratory findingswith the project participants (field operators and manufacturers), and at theinitiative of one particular manufacturer, a new valve design (HIVAC) wascompleted, manufactured and field tested at numerous sites, The results of thefield tests presented in the paper, showed that an increase in flow rates(between 60% and 110%) occurred over conventional API valves used at the samesites.

Introduction

The design and operation of rod bottom hole oil pumps, used in approximately80-90% of artificial lift wells, reached a mature stage during the period1970–1980. 1 Improved diagnostic tools for evaluating theirperformance appeared during the 1980's; these tools included automateddynamometer cards that aided in a rapid and relatively inexpensivede-convolution and interpretation of familiar load-strokediagrams2,3. During the last decade the massive development ofheavy oil reservoirs in Alberta, Saskatchewan, and Venezuela and the widespreaduse of horizontal and deviated wells for both conventional and heavy oilreservoirs drilling has imposed additional constraints on rod pumpapplications.

In Alberta, thermal projects have always experienced difficulties with pumpingoperations. In 1988 a survey conducted by the Alberta Department of Energy-Oil Sands and Research Division (formerly AOSTRA) found that the most commonproblems encounterel1 were pump seizure (customarily related to sand-ladenfluids), and pump inefficiencies due to stearn and non-condensiblegases4 A multi-disciplinary team consisting of ADOE, OSRD, ARC, 8major fields operators and 4 rod pump manufacturers in Alberta was formed toaddress those problems. Although the major objective for the committee was toimprove existing thermal pumping technology, more general applications tohorizontal well and high gas/oil ratio situations also were put at a highpriority. An overview of the program and its major laboratory achievementsduring 1988–1991 have been discussed elsewhere4. This paperdescribes further laboratory observations on valve hydrodynamics withconventional and slanted wells that were obtained during 1991–92, as well assignificant field results that were achieved using a novel valve design.

A pumping efficiency (denoted by ?v equation 1) as low as 10% wascustomarily reported4 for severe steam breakthrough situations; anefficiency 70% was averaged for all situations not involving steam.

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