Regardless of what method or program is used to predict loads, once the equipment is installed and the well has stable production and fluid levels, it is recommended that a dynamometer survey be run with a load-capable dynamometer attached to the polished rod. However, the ID of the seating nipple determines the fluid load that must be lifted to unseat the pump. There has been a long history of work trying to model or design sucker-rod strings.
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The harder the steel is, the more susceptible it becomes. Thus, more production may be possible from the well with a tapered string than a straight string using the same-diameter pump.
Where the yield strength of a rod string sepc necessary in calculations, it is recommended that if the manufacturer is not known, a minimum yield of 60, psi for Grade C and Qpi and ofpsi for Grade D should be used.
An SPE paper by Powers  considers the factors that enter into the decision about when to replace the entire rod string after sustaining the calculated number of failures. In a noncorrosive environment, the endurance limit of steel is primarily determined by the maximum stress, the range of stresses, and the number of stress reversals.
The current edition provides for two classes of couplings: Thus, slimhole couplings are not as strong as the full size.
They are most commonly placed adjacent to the polished rod at the top of the rod string, on top of the downhole pump for handling purposes, and on top of the polished rod with appropriate couplings to prevent the string from falling downhole if the polished-rod clamp slips.
This is especially problematic if field welds are made and the rods are used in an inadequately protected corrosive environment. However, the Sspec of the seating nipple determines the fluid load that must be lifted to unseat the pump.
The development of the wave equation for sucker-rod lift by S. However, this rod type may be more notch-sensitive and may require better handling and corrosion protection than normal API-type rods. As with any specialty equipment, good field testing and records for several years in which good handling and operating practices were followed are required to prove the benefit for any of these non-API rods.
The connectors used at the pump or at the top of the sinker bars were the weakest portion of the flexible strand. Corrosion pits may have rounded or notched shape; notch-shaped pits are more serious and are more likely to occur in Grade D rods psec in Grade C rods.
This is because it has to support the weight of the rest of the small-diameter rod load, the pump and the very large fluid load on the gross seating nipple area. Corrosion, scale, and paraffin deposits may accelerate such failures.
Subsurface equipment for sucker-rod lift. Ideally, a rod string should be a continuous taper from top to bottom. Thus, they could be used in a hydrogen sulfide H 2 S environment in which the strength of Grade C rods is exceeded. The manufacturer of specialty or non-API rods should be consulted for their recommended CD values and makeup procedures.
This hardness is normally accomplished by the spray-metal process. Currently, there is no recognized formula for 11v overtravel when a mixed FRP and steel rod string is used.
The primary factor determining the proportion of each size of rod in the rod string is the size of the pump. A study of several FRP string-design analyses indicate that rod-string overtravel may be approximately psec to the following:. Columns 6 through 11 in Table D. A detailed discussion and development of these formulas is provided by Zaba. Old pony rods normally should not be used in the load-carrying part of a new rod strings. Further soec by Hermanson  using the area relationships and allowable strength of the different grades of steel rods resulted in different apo factors, which are included in API RP 11BR.
The primary factors affecting the selection and sizing of rods and the rod system are as follows:. The taper percentages published in RP 11L were calculated from the Neely,  procedure by assuming several parameters like pumping speed, polished rod stroke length, etc.
API Spec 11B(27th )_图文_百度文库
However, typically only one grade of rod is used in the string to avoid mixing during running and pulling operations. These rods have been effectively used to produce approximately BFPD from a depth of approximately 14, ft.
Carrying out the various procedures described in this section can greatly reduce operating costs and make production more efficient and economical. The advent of the personal computer and its continued developments of power and speed allowed more developments of rod-string simulators, including: Class T through hardened coupling has a Rockwell C hardness range of minimum 16 and maximum spsc, and Class SM surface hardened has a minimum Rockwell C surface hardness of