In this paper, the experiences of the use of a novel rod string design to improve the Run Life of the PCP system in highly deviated and tortuous wells are shared. These wells presented premature and recurrent failures in the rod string. The results are contrasted with real cases in the same wells where the conventional and continuous rods failed in a brief period.

Through a detailed RCFA (Root Cause Failure Analysis), it was determined that the main failure mechanism was due to fatigue in high DogLeg areas. To solve this problem, design simulations were carried out, by locating hollow rods in these zones and applying the Von Misses method to determine the effective stress due to torque and axial load, comparing these values with previous designs.

The hollow rod geometry allows for a greater polar moment of inertia, which causes the effective stress to be lower in high DogLeg points, making the string more resistant to axial and torsional stresses. The comparison was made between two widely used types of rods in two wells of a Colombian Field, with angles up to 50 degrees and DLS of 7.8° / 100 ft. The major benefit of the implementation of this design is that it managed to raise average run life from 45 days to 180 days, without presenting failure in the rod string.

This study is important because operating companies must reduce operating expense (OPEX) by optimizing the components in artificial lift systems, like the rod string in PCP, minimizing the frequencies of well interventions.

The methodology and design presented in the article can be replicated for other wells that have similar geometries and operating conditions to those of the explained cases, with the application of hollow rods as an alternative to conventional designs.

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