What IS Reliability - Part 4

Here is the 4th and final article in the "What IS Reliability"

F). Reservoir/Fluid Characteristics:?????????? Reservoir characteristics are critical in determining what the inflow of the well is, & what sort of lift is required. This dovetails with the system sizing and selection that will be explained in section (H). The PI or IPR of the well will determine what is needed however often times, the equipment installed is either undersized or oversized for the conditions at a given period of time in the life of the well. It is not always the case that the proper artificial lift system can be used for the entire swath of conditions for the life of the well, but generally for given segments. A high producing fluid level at the start of the well can quickly drop leaving the ALS undersized for the pressure and rate desired. On the flip side, the ALS can also be oversized if the producing fluid level remains high. This is where discussions between the production team and the reservoir team should be talking so that an accurate drawdown curve can be developed allowing one to properly evaluate the lift/rate combination that needs to be addressed. Inaccurately understanding the reservoir performance can lead to a failure to the artificial lift system.

On the fluid characteristic side of things, understanding the fluid viscosity, corrosivity, etc. can provide critical information that affects the necessary TDH (Total Dynamic Head) requirements and materials of construction (I.e., corrosion &/or abrasion resistant materials). Not knowing the fluid characteristics can and will result in a premature failure.

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G). Assembly:??? How the artificial lift systems are assembled can be a source of failure if done incorrectly. This can be either in the factory, or in the field. In the factory, human error can creep in, and equipment can be mis-assembled, minor components missed, torque values applied incorrectly, or even components mis-assembled due to the lack of proper assembly tools. A failure can occur due to failure to follow a procedure, or having a procedure that is inadequate and more prone to a failure or mis-assembly occurring. Once determined, proper training can be done, competencies regularly verified, or tooling either purchased, repaired or re-calibrated.

Although a different environment, improper assembly in the field can also occur. Servicing components improperly can lead to premature failures. In the case of ESPs, topping off motor oil and ensuring that all the air bubbles are out of the system can be a source of failure. Inclement weather can and often does, affect the efficacy of this being done properly. Additionally, when tightening the drain/fill plugs, improper tightening can affect the lead washers either by under or over compressing them resulting in a possible leak path from well fluids.

In the case of PCPs, proper torquing of the stator-to-tubing connection as well as the entire production tubing string will ensure that the stator/tubing will not back-off when operating or during back-spin. Likewise, proper tightening of the rods/rod couplings will ensure that there are no premature rod/coupling failures. Not using a circumferential displacement card for the rod size and grade may result in incremental make-up during operation and can often result in rod pin failures.

When running RRPs, there are both downhole pump as well as surface unit assembly/set-up concerns. On the downhole pump portion, proper tightening of the standing and traveling valve components will ensure that they do not come unscrewed. Regarding the surface components of RRPs, proper set up of

the pumping unit components such as the counterbalance weights, bridle, gear reducer, polished rod clamp, etc. all have their respective assembly/set-up criteria all of which if not followed properly, can result in a premature failure or reduced run time.

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H). System Sizing/Selection:??????? In the sizing and selection process for any artificial lift system, the accuracy of the data used to size or select the system is in direct proportion to the failure rate and overall run time. If “general field data” or “generic” application data is used, the reliability of said artificial lift system (regardless of lift method) will be greatly reduced and the propensity of a failure increased.

This section is tied heavily to the earlier section on Application. If the application data is generic or general in nature, or if some of the data is “guessed”, than the sizing and selection of any artificial lift system will be inaccurate. The level of inaccuracy will be in direct proportion to the inaccuracy of the application data.

Often times, artificial lift systems are sized or selected for other reasons - - component availability or standardization of what is run across a wide range of wells, within a given field, or region. In these cases, there will be a percentage of the selected artificial lift system that is within the acceptable application range, while others will be on the fringes, or even outside of the acceptable application range. Many times, it is a commercial decision.

Although there may be reasons for the selections made, one needs to understand that where these systems fall within the bell curve of the acceptable range can and will affect the probability of failures and their frequency.