GRE-Lined Tubulars in Caspian Wells Prove Integrity, ESG Benefits
Chris Carpenter_
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 230417, “15-Year Case Study of GRE-Lined Tubulars in Caspian Water-Injection Wells: Field-Proven Integrity and ESG Benefits,” by Bahram Novruzaliyev, SPE, BP; Agshin Mammadov, SPE, Maxtube; and Fady El-Daby, BP. The paper has not been peer-reviewed.
_
This paper presents a 15-year field case study on the use of glass-reinforced epoxy (GRE)-lined carbon-steel tubing in offshore water-injection wells in the Azeri-Chirag-Deepwater Gunashli (ACG) field in the Caspian Sea. Since April 2008, more than 60 completions have been equipped with GRE-lined, 7.000-in., 29.00-ppf API 5CT-compliant tubing with proprietary metallurgy for sour-service applications and a threaded-and-coupled premium connection, making ACG one of the world’s largest and longest-running offshore GRE deployments.
Field Overview and Application Scope
The ACG field is the largest offshore oil development in the Azerbaijan sector of the Caspian Sea. The ACG covers an area of approximately 432 km2 and comprises seven fixed offshore platforms commissioned between 1997 and 2024, with facilities for production, injection, compression, and processing, all linked by extensive subsea pipeline infrastructure to the onshore Sangachal terminal near Baku.
To maintain reservoir pressure and support recovery, ACG employs both seawater injection (SWI) and produced water reinjection (PWRI). Raw seawater is sourced directly from the Caspian Sea. While moderate in salinity compared with open oceans, the injected fluids remain corrosive because of chloride ions, dissolved oxygen, and biological activity indicated by elevated acetate in produced water. PWRI further introduces additional corrosive constituents, including CO2, trace hydrogen sulfide (H2S), hydrocarbons, and elevated solids loading, creating a service environment capable of reducing the life of unprotected carbon steel tubulars significantly.
The decision to adopt GRE lining for ACG injection wells was influenced by successful deployments in the North Sea and positive qualification test results, coupled with the operator’s strategy to standardize material selection for water-injection service to either GRE-lined carbon steel or 25Cr corrosion-resistant-alloy (CRA) tubing. Initial requests for GRE-lined tubing were raised in early 2004, leading to fieldwide adoption in April 2008. Since then, injection wells at ACG have been completed using internally GRE-lined tubing with proprietary metallurgy for sour-service applications and a threaded-and-coupled premium connection as the standard for both SWI and PWRI service.
Typical operating constraints at ACG include injection pressures between 25–40 MPa and injection rates of approximately 3,200–12,700 m3/day, depending on reservoir requirements and well configuration. Downhole temperatures generally range from 65–75°C, with lower wellhead temperatures caused by cooling during injection. Offshore intervention schedules, particularly for subsea wells, are further influenced by seasonal weather conditions in the Caspian Sea, which can limit rig availability and crane operations.
Material Selection Rationale: CRA vs. GRE
Technical Properties.
CRAs, particularly 13Cr martensitic stainless steel and 25Cr super duplex stainless steel, historically have been considered for injection service because of their resistance to chloride-induced corrosion. In the ACG, a single water-injection well completed with 13Cr tubing (converted from an oil producer in 2001) provided only limited field exposure.