Technology-Driven Well Integrity Repair Using Hybrid Intelligent Coiled Tubing with Real-Time Diagnostics and DFOS Monitoring

Abstract Geothermal wells, particularly in high-enthalpy hot water systems with injector-producer configurations, are subject to thermal and geochemical stresses. High-formation temperatures and corrosive components, as dissolved CO2, H2S, and chloride-rich brines, can reduce the effectiveness of conventional chemical treatments. These conditions accelerate localized corrosion processes, including pitting and crevice attack, that compromise completion integrity. A technology-driven remediation strategy is critical to extending well service life and ensuring long-term sustainability of geothermal assets in the context of the energy transition. This paper presents a case study detailing an advanced well integrity remediation executed using hybrid coiled tubing technology (HCTT), by integrating both electric conductor and distributed fiber optic sensing (DFOS) functionalities. The presence of the electric conductor enabled deployment of a high-resolution multi-finger caliper for accurate casing damage characterization and powered a real-time monitoring BHA, eliminating battery constraints during critical operations as patch setting cycles. Concurrently, the integrated fiber-optics enabled DFOS acquisition immediately post-patch installation, providing real-time thermal and acoustic surveillance for leak detection, eliminating the need for pressure testing, a key advantage in this scenario where applying pressure could have imposed excessive mechanical load on the casing, potentially leading to structural failure. The intervention was engineered into the following phases: Casing Preparation, in-situ mechanical cleaning via abrasive slurry jetting to remove rust, scale, and debris from the casing surface, to ensure patch-to-metal contact, improved caliper data, and eliminated the need for mechanical standoffs; Damage Diagnostics, high-resolution electric multi-finger caliper to localize and quantify casing defect; Restoration and Integrity Verification, deploying an inflatable casing-patch, followed by DFOS acquisition to validate mechanical setting and hydraulic isolation. To enhance thermal signal contrast for real-time DFOS interpretation, a temperature differential of approximately 30-40 °C was induced between the well and the annular injection fluid. This was achieved by implementing a cryogenic cooling loop—a serpentine assembly of hoses through which liquid nitrogen was circulated—allowing the injected water to be sufficiently cooled. Potential thermal anomalies were captured via DTS, while DAS responses were stimulated by flow noise, collectively enhancing the detection sensitivity across the repaired interval. The HCTT-based workflow enabled precise diagnostics, effective mechanical remediation, and real-time, non-invasive integrity verification. DFOS acquisition provided high-resolution leak detection without applying mechanical stress to compromised completion. This case confirms the technical and economic viability of full-spectrum HCTT as a scalable, non-invasive solution for long-term well integrity management in high-temperature, high-corrosivity environments. The flexibility of HCTT proved to be a key advantage, enabling the Operator to execute the remediation workflow, without mobilizing additional service providers. Real-time DFOS immediately after patch installation enabled efficient and non-intrusive verification of well integrity, eliminating the need for pressure testing and avoiding mechanical stress on the compromised completion.