Glass-Reinforced Epoxy Effective Alternative to Alloys in Gas Wells
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The complete paper describes an operator’s experience in confirming glass fiber-reinforced epoxy (GRE) as an effective alternative to high-grade corrosion-resistant alloys (CRA) to extend tubing life in high-velocity gas wells. Laboratory testing and applications in several fields, both on and offshore, and in oil-production and water-injection wells and surface-gathering lines, demonstrate that, when used within the operating limits, GRE can extend tubing life and provide life-cycle cost savings.
The material has been intensively tested in the past to determine characteristics and capabilities. Mechanical properties, fatigue resistance, chemical compatibilities, connection properties, and abrasion trials have been proved by specific laboratory tests and field trials, demonstrating that GRE can be applied inside production tubing strings. API RP15CLT, first issued in 2007, provides guidelines for the design, manufacture, qualification, and application of composite-lined carbon-steel downhole tubing in the handling and transport of multiphase fluids, hydrocarbon gases, hydrocarbon liquids, and water.
Carbon steel guarantees the system’s mechanical resistance, and the internal GRE liner ensures corrosion resistance. GRE provides outstanding corrosion resistance, even in very aggressive environments.
For oil-well applications, the system consists of a GRE resin composite liner inserted inside a low-alloy carbon steel tubing with a cement grout (Fig. 1). The grout transfers pressure directly to the steel tubing even if there is little or no bonding between liner, grout, and metal.
The end of the liner is protected from mechanical damage by a GRE end cap (flare) or a T-end flange. A polymeric corrosion barrier ring usually provides the continuity of the corrosion barrier across the coupling between two adjacent flares. The lining is lightweight, adding no more than 13% of the weight of the steel pipes and eliminating the need for additional lifting equipment.
The operator has been involved in the development of deepwater gas fields with high production rates and sour environments. On the basis of corrosion assessments performed on actual field conditions, CRA (high nickel content) material was selected as most suitable for the production tubing string. Following positive experiences with the installation of GRE, the company decided to evaluate its performance in potentially high-erosion conditions, aiming to find an alternative material to high-grade CRA for installation in high-velocity gas wells that would reduce cost and delivery time. The GRE liner was selected as a cost-effective alternative to high-alloy materials starting from 2005, when GRE was successful in reducing onshore workover costs and extending the life of carbon-steel tubing in oil producer wells with high carbon dioxide and water cut, to recent installations offshore Norway in water injection wells with highly corrosive injection fluids.
The complete paper summarizes the testing and application range of GRE in corrosive environments and, through collaboration with the Polytechnic University of Milan, high-flow, direct-impact erosion testing using a continuous flow loop and a nozzle-directed solids-impingement-testing system.
Laboratory Test Results
The direct-impact test confirmed that GRE shows a high resistance to erosion at high velocities and solids loadings. As a reference, similar tests were performed on nickel alloy 625 material (same sand size, jet velocity, time and 90° impact angle), and provided values very close to those obtained for the GRE composites. Results could be considered comparable to those obtained on the experimental analysis performed by the Polytechnic University of Milan.
Visual inspection of the internal surface of the GRE coating following the straight pipe flow-loop erosion revealed no sign of erosion. Similarly, the thickness of the GRE coating remained unchanged, further confirming the absence of measurable or detectable mass removal.
Operator Field Experience
The GRE liner has been successfully applied in several fields, onshore and offshore, as tubing corrosion protection in oil-production wells, water-injection wells, and surface flowlines. The complete paper summarizes field applications in north Africa, northeast Africa, the Middle East, and the Barents Sea (Fig. 2). The feedback from the field cases confirmed that, when used within the operating limits, the GRE material represents a valid option for life extension and lifecycle cost savings.
Economic analyses comparing GRE liners with carbon steel and CRA for water-injection and oil-production wells in onshore and offshore conditions reveal that GRE cost is more than double that of the tubing in bare carbon steel. However, alternative CRAs, which have sometimes been considered, have proved more expensive than the one used in this paper.
- GRE composite material has been extensively tested by operators and manufacturers according to API standards and customized testing protocols over the last 20 years.
- The additional tests carried out in independent laboratories by the operator confirmed and extended confidence in the material’s performance at high gas-flow rates.
- Both direct-impact and straight pipe test results showed very good erosion resistance of the material, comparable to that of a nickel alloy 625 sample assessed under similar conditions.
- The two laboratory tests verified the erosion resistance of GRE material with regard to its suitability for use in high-velocity gas wells in challenging conditions that simulated actual well environments with sand production, and confirmed that GRE had the effective erosion properties required.
- According to the successful laboratory tests in such critical conditions, the operator at the time of writing was evaluating the potential application of GRE material in upcoming gas-production projects in which sand or solid erosion issues could affect the tubing-string integrity and could have a significant effect on costs.
- Feedback from field applications demonstrates that, when used within the operating limits, this material represents a valid option for life extension and life-cycle cost savings.
Glass-Reinforced Epoxy Effective Alternative to Alloys in Gas Wells
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04 August 2020