Double-layer SST Optical Cable - Fiber In Metal Tube (FIMT) - Oil Well Sensing Optical Cable - High Temperature Optical Cable

Alias: Double-Layer Downhole Fiber Cable, Tube-in-Tube High-Temp Cable, Hydrogen-Resistant PSC Fiber Cable, Pure Silica Core Oil Well Fiber, Alloy 825 Dual-Tube Sensing Cable, 1/4" Heavy Duty SST Fiber Cable, PDS (Permanent Downhole Sensing) Cable, Acid-Resistant Geothermal Cable.

1. Product Overview of OFSCN® Double-Layer High-Temperature Downhole Fiber Optic Cable

The OFSCN® Double-Layer High-Temperature Downhole Fiber Optic Cable is engineered for the most demanding environments in oil and gas exploration, ultra-deep well monitoring, and complex acidic geothermal reservoirs. Featuring a unique "Tube-in-Tube" double-layer seamless metal encapsulation, this cable provides a dual physical barrier. Combined with Pure Silica Core (PSC) fiber options, it effectively eliminates signal attenuation caused by hydrogen ingress at high temperatures. The heavy-duty outer tube provides structural support, while the inner precision tube offers secondary hermetic protection, making it the ultimate choice for Distributed Fiber Optic Sensing (DTS/DAS/DSS) in extreme downhole conditions.

2. Mechanical Structure & Physical Parameters of OFSCN® Double-Layer High-Temperature Downhole Fiber Optic Cable

This cable is available in 316L Stainless Steel (Standard) and Alloy 825 (Extreme Acidic Environments) versions.

Parameter	316L Stainless Steel (Standard)	Alloy 825 Nickel-Alloy (Option)	Remarks
Outer Tube Diameter	6.35 mm (1/4")	6.35 mm (1/4")	Custom 4.8mm (3/16") available
Outer Tube Wall	0.9 mm	0.9 mm	Primary mechanical load layer
Inner Tube Diameter	3.6 mm	3.6 mm	Secondary hermetic barrier
Inner Tube Wall	0.3 mm	0.3 mm	Balancing shield & conduction
Theoretical Weight	~148 kg/km	~151 kg/km	Density of 825 is slightly higher
Tensile Strength	> 10,000 N	> 11,000 N	Superior high-temp strength
Crush Resistance	> 150 MPa	> 160 MPa	Resists extreme formation pressure
H2S / Chloride Resistance	Good	Excellent	825 is ideal for sour wells
Min. Order Qty (MOQ)	1,000 Meters	1,000 Meters	For standard production runs

3. Optical Fiber Configurations & Temperature Ratings of OFSCN® Double-Layer High-Temperature Downhole Fiber Optic Cable

Flexible configurations are available based on coating material and core glass type:

3.1 Advanced Fiber Core Options

• Hydrogen-Resistant Version (PSC): Utilizes Pure Silica Core (PSC) fiber. The pure silica structure inhibits the formation of hydroxyl groups (-OH) at high temperatures, preventing "hydrogen darkening" at the material source.
• Standard Version: Utilizes standard Germanium-doped fiber (suitable for low hydrogen concentration environments).

3.2 Temperature Ratings & Product Links

Rating	Recommended Fiber Model	Key Advantage
200°C Grade	OFSCN® 200°C Polyimide Fiber	No coating delamination; stable heat transfer
300°C Grade	OFSCN® 300°C SM PI Fiber	Specialized for SAGD & Geothermal wells
300°C Grade	OFSCN® 300°C MM PI Fiber	Specialized for SAGD & Geothermal wells

Customization: Both grades support any combination of Single-mode (SM), Multi-mode (MM), or Pure Silica Core (PSC) fibers.

4. DFOS Compatibility Analysis of OFSCN® Double-Layer High-Temperature Downhole Fiber Optic Cable

Technology	Recommended Configuration	Problem Solved in Downhole
DTS (Temperature)	Multi-mode PSC (MM-PSC)	Prevents temperature drift caused by hydrogen darkening.
DAS (Acoustic)	Single-mode PSC (SM-PSC)	High rigidity of double-layer tubes transmits acoustic waves efficiently.
DSS (Strain)	200/300°C PI Coated Fiber	Hard PI coating ensures accurate strain transfer between layers.

5. Connectivity & Termination of OFSCN® Double-Layer High-Temperature Downhole Fiber Optic Cable

• Field Installation: Field Fusion Splicing is recommended. Both inner and outer tubes must be sealed using specialized dual-stage compression fittings or orbital welding.
• Pre-terminated: FC/APC or FC/PC high-temperature connectors can be pre-installed for surface-side or wellhead interface.