High-Density Polyethylene Liner Safeguards Against Corrosion and Wear
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Production tubing in mature fields in the Magdalena Department’s Middle Valley in Colombia has shown a run life between 180 and 300 days, with failures mainly caused by corrosion and abrasive wear or friction mechanisms. Extended use of high-density polyethylene (HDPE) liner in flow and collector lines with corrosion and abrasion problems has resulted in positive results. The complete paper presents the results of evaluation of laboratory and demonstration trials of HDPE liner to mitigate premature failures and prolong the run life of production tubing.
Root-cause analysis determined that failures in production tubing in the mature Casabe and Cantagallo fields could be the result mainly of corrosion by the multiphase fluids transported or as the result of wear mechanisms caused by contact between the internal wall of the tubing and the sucker rod in artificial-lift systems.
To solve this problem, HDPE liner was evaluated in the laboratory and implemented in a pilot-scale test. Results proved its ability to absorb abrasion impact from sand particles and resist CO2 corrosion. After 12 months in service, the HDPE liner demonstrated its compatibility with aggressive fluids, remaining thermally stable with no structural variation and absence of swelling, softening, and blistering. After 6 years, the pilot remained failure-free and operationally active.
On the basis of these results as well as other research in the literature, HDPE liner was proposed as a downhole alternative to prolong run life of critical wells in the Casabe field. To this end, HDPE lining for carbon steel tubing was developed and manufactured in Colombia through an engineering process that included materials specification, prototype design, mechanical stress analysis, laboratory tests in simulated downhole conditions, redesign of the prototype, and optimization of the production process. To validate the technology, the downhole HDPE liner was installed in three producing wells with progressive-cavity-pump (PCP) artificial-lift systems and a run life of approximately 300 days. After 400 days of service, well intervention was performed not related to tubing; the tubing had not experienced damage and was reinstalled, with a three- to sixfold run-life increase.
HDPE Liner Technology
HDPE is known for its ability to inhibit corrosion, improve flow fluid because of a lower friction coefficient compared with carbon steel, and resist abrasive wear because of high tenacity properties. The HDPE (PE-100) is used in contact with multiphase fluids (water/crude oil/gas) with maximum service temperature of up to 60°C, depending on the manufacturer. According to laboratory tests, the resistance of HDPE to abrasive wear and corrosion is approximately three times that of carbon steel.
Thermoplastic-lined downhole tubulars had been installed in more than 70,000 wells over a period of approximately 25 years, as described in the literature. The use of HDPE liners for protection against abrasive wear also has been studied with regard to slurry erosion at temperatures from 35 to 65°C. The HDPE manufacturing process is detailed in the complete paper.
Downhole Simulated Laboratory Tests
On the basis of the performance seen in laboratory abrasion and corrosion tests performed on extruded HDPE pipe sections in simulated Casabe-field-flowline conditions, a pup joint with a 3.5-in. outside diameter with HDPE liner was evaluated under simulated downhole high-pressure/high-temperature (HP/HT) conditions. For these tests, 20-cm sections of the HDPE-lined pup joint were immersed in production water at a temperature of 60°C and a pressure of 6.89 MPa for 30 days. The sample sections were characterized by visual inspection, hardness measurement, erosion resistance, and differential scanning calorimetry (DSC) before and after an HP/HT test. Visual inspection allowed identification of anomalies and defects in the HDPE liner, such as leaks, blistering, signs of collapse, and discoloration. The erosion resistance of the HDPE samples was evaluated using water as the fluid medium. The slurry fluid was composed of 690 g of sand with particle-size distribution between 0.15 and 0.22 mm mixed in 30 L of water and projected on the HDPE for 90 minutes. Thickness was measured before and after slurry projection to determine its abrasive effect in terms of wall thickness loss.
DSC tests were conducted with a temperature precision of ±0.01°C and a calorimetric precision of ±0.1%. Samples of new and exposed HDPE with a weight of approximately 19 mg were placed in an aluminum pan and exposed to nitrogen (flow rate 50 mL/min). The samples were heated to 230°C at 10°C/min with isotherms of 20 minutes. The changes in melting temperature, fusion enthalpy, and crystallinity were determined.
Results and Analysis of Laboratory Tests
The HDPE liner section, after 30 days of immersion in production water at 60°C and 6.89 MPa, was not adversely affected. Visual inspection did not reveal leaks, blistering, signs of collapse, discoloration, swelling, or softening in comparison with HDPE liner sections in a new condition.
Erosion resistance increased slightly in the HDPE liner section exposed to HP/HT conditions, indicating that the toughness and ductility of thermoplastic polymer, which is directly related to its ability to resist the start of permanent distortion and impact-absorbed energy caused by erosive wear, remained unchanged even after immersion at the previously described conditions.
The HP/HT test in production water affected neither thermal properties of the HDPE liner nor hardness and erosion-resistance properties. The difference in the melting point of HDPE after the immersion test is within the range expected (±5°C) of thermoplastic liners. Additionally, the crystallinity calculated from the heat of fusion of 100% crystalline HDPE shows an unchanged polymeric structure.
Downhole Field Tests
After the laboratory tests, a field test was performed to validate the behavior of the HDPE liner in downhole conditions. For this test, the HDPE lining tubulars of 3.5‑in diameter manufactured in Colombia were installed in three producing wells in the Casabe field with PCP artificial-lift systems and a run life of approximately 150 days.
Results and Analysis of Field Test
In February 2019, after 13 months of service, the HDPE-lined tubing in Well 2, which was intervened for reasons not related to tubing, was found to be in excellent condition without evident damage and was run back downhole. HDPE liner tubing presents a run life between three and six times longer than that of bare tubing. This behavior indicates that, in abrasive-wear and CO2-corrosion conditions, the lined tubing is an effective option to reduce downhole failures and intervention costs.
After the installation of the liners in the three pilot wells, economic evaluations were conducted to establish the savings shown in Fig. 1. The closing date for the evaluation was 22 October 2019.
HDPE-lined tubing has proved to be an effective alternative to reduce tubing failure caused by wear and corrosion, thereby reducing intervention and lifting costs in beam-pumping or PCP wells and extending run life significantly. The results of laboratory and field tests indicate that HDPE-lined tubing manufactured in Colombia with diameters of 3.5 and 4.5 in. can be considered technical and economically viable alternatives in wells (preferably deviated) with artificial-lift systems in environments with sand, friction with rods, or internal corrosion.
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04 August 2020