Nonmetallic-Based Tubulars Provide Superior Integrity, Cost Savings

Abstract

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 214647, “Operational Experience From the Implementation of 21 Wells With Nonmetallic-Based Downhole Tubing: From Pilot to Large-Scale Implementation,” by Mohamad H. Ahmad, ADNOC. The paper has not been peer reviewed. _ Tubular glass-reinforced-epoxy (GRE) lining technology has been applied globally since the 1960s in eliminating downhole tubular corrosion. Compared with conventional carbon steel, which can experience frequent failure, GRE-lined carbon steel provides long-lasting protection, resulting in huge savings in life-cycle cost. The operator implemented this technology for a successful trial of water-disposal wells. In the complete paper, the authors share the data from caliper logs run into, and the inspection of tubing pulled from, these disposal wells after 4 years in service. Tubular Corrosion in Operator Assets A growing emphasis on water disposal was inevitable because so much water was being produced with increased water cut and production. ADNOC Onshore operates almost 200 water-disposal wells. However, corrosion has been a common problem in these wells, such that a failure has been reported every 1–2 years. Use of corrosion-prone carbon steel for disposal strings has led to integrity issues and the need for expensive workover jobs that could cost between $1.5 million and $2 million per job. Fiberglass GRE Lining Since 2014, the operator has run 19 water-disposal wells with GRE-lined carbon steel strings. No failures have been reported, and inspections have been successful. Fiberglass tubular lining protects the internal surface of the tubing or casing inside the steel joint. Cement is pumped into the annulus between the GRE-liner outer diameter (OD) and the steel‑pipe inner diameter (ID). The final product is a completely corrosion-protected string, even under the connection area, where accessories called flares and corrosion barrier rings (CBRs) are installed (Fig. 1). The mechanical capability of the system is maintained by the steel pipe, while the internal fiberglass liner provides reliable corrosion resistance. Fiberglass Liner. The fiberglass liner shows excellent resistance in corrosive environments. As per tested and as per the manufacturer’s data sheets, the fiberglass lining system can be used in temperatures of up to 145°C, depending on hydrogen sulfide and CO2 levels in the flowing fluid. Besides being corrosion‑resistant, fiberglass lining improves the flow rate of the flowing water or oil because of the superior surface-energy properties and manufacturing quality of the liner material. The thickness of the liner varies according to the tubing size (diameter). Cement. The cement transfer applies pressure directly to the steel pipe. The cement does not bond the fiberglass liner to the steel and allows relative micromovement between the fiberglass liner and the steel pipe resulting from the difference in the thermal expansion coefficient of these two materials. Being alkaline, the cement tends to neutralize the possible presence of acid gases migrating in the fiberglass‑steel annulus; this further reduces the possibility of carbon-steel-pipe corrosion.