Production Well 205 has a daily fluid output of 7.9 tons, daily oil output of 2.07 tons, and water content of 73.8%. The well was overhauled and installed with lined composite pipes on January 1, 2018.Before the installation of lined composite pipes, this well had been overhauled for 6 times throughout 2017. The detailed overhaul causes are listed as follows:
February 26: Pump stuck overhaul caused by ball seat blockage from oil sludge inside the pump;
April 24: Overhaul due to sucker rod fracture at No.104 and tubing fracture at No.111 caused by corrosion;
June 28: Overhaul due to tubing fracture at No.118 caused by corrosion and eccentric wear;
August 2: Overhaul due to tubing fracture at No.138 caused by corrosion and eccentric wear;
August 26: Overhaul due to tubing fracture at No.135 caused by corrosion;
December 31: Another pump stuck failure caused by oil sludge blockage, followed by well overhaul and overall replacement of lined composite pipes.
This well features extremely complex downhole conditions, including severe corrosion, eccentric wear and scaling problems.
In 2017, its shortest overhaul interval was only 57 days, with an average overhaul cycle of 75 days. Frequent well failures severely restricted the normal crude oil production. After the well overhaul and lined composite pipe replacement implemented on January 1, 2018, no tubing failure occurred until December 16, 2018, with a continuous service cycle of 349 days. Compared with the average overhaul cycle of 75 days in 2017, the pump inspection cycle was prolonged by 274 days, equivalent to a 4.65 times extension.
Performance Conclusion of UHMWPE Lined Tubing
1. Excellent Well Adaptability
After the UHMWPE liner is installed inside Φ73 mm tubing, the inner diameter becomes Φ55 mm. The pump diameter of pumping wells is Φ44 mm or smaller, and conventional logging tools for injection wells are less than 50 mm. Therefore, lined tubing can satisfy the demands of most oil production wells and water injection wells.
2. Outstanding Eccentric Wear Resistance
The sliding friction coefficient between UHMWPE liner and steel ranges from 0.07 to 0.11, half of the steel-on-steel friction coefficient. Eccentric wear in pumping wells arises from wellbore deviation, pipe bending and elastic deformation of production tubing strings. After running lined tubing at positions prone to eccentric wear, eccentric damage to production strings can be effectively suppressed, and the service life of both tubing and sucker rods can be prolonged.
3. Significant Economic Benefits
After deploying UHMWPE lined tubing, the matched sucker rods can not only eliminate downhole eccentric wear, but also lower running resistance of rods. The rod load and minimum stress at the bottom of the rod string decrease remarkably, as does the gap between the maximum and minimum rod loads. Lower minimum bottom stress reduces the risk of rod buckling under compression, thereby mitigating unstable eccentric wear. Meanwhile, the polished rod suspension load of pumping units is cut down, and the overall system efficiency is improved.
