In Staatsolie, as of December 2013, there were 1549 shallow wells from its 3 oilfields. One thousand one hondred and thirty (1130) of these were in the Tambaredjo field (TAM field). In the 3 decades of its operations, the prime mechanism for lifting the 15.6oAPI crude to surface has been with progressive cavity pumps (PCP). The down hole pumps are surface driven and installed at an average true vertical depth (TVD) of 1000 ft. Oilfield best practices are employed in the design, installation and operation of the production strings and pumps.
In the period 2008-2012 an average 580 down hole failures occurred annually of which 54% was caused by tubing leaks, with a repetitive frequency of up to 6 faillures per year on individual wells. Visual inspection of internal tubing’s have shown that the principal failure mechanism stems from rod tubing wear (abrasion caused by the rotational motion) exacerbated by the corrosiveness of the produced fluids. Most of the tubing wear occurs at the tubing body in direct contact with the rod couplings. It is found that most tubing leakages (up to 70%) occur on the lower part of the tubing string above the pump. Previous installation of shorter rods above the pump, which is causing a high eccentrically movement of the rod string, also increased the occurrences of these failures directly above the pump.
In an effort to reduce these tubing failures, an eight-well pilot program was commenced to install rod guides in wells with the highest failure rate and to install a sucker rod of 25 feet right above the pump. These eight wells were selected based on their high tubing failure rates. Although the program is still being conducted, preliminary results thus far have been quite promising in these wells. In four (4) wells, the work-over frequency was reduced from average 5 to 3 jobs per annum resulting in 40% reduction. The remaining 4 wells are still producing after an average 5-month period without any tubing failures.
This paper presents the approach and strategy used to minimize rod-tubing wear in shallow vertical well applications based on the outcome of the pilot test.
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