Downhole Cable Diameter Reduction via Nested Coaxial Design
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Solution Overview
Problem
Commercially available TEC/TEF downhole cables with both optical fibers and electrical conductors are too large and heavy for coiled tubing applications, and small-diameter TEF cables lack sufficient current carrying capacity due to high electrical resistance of their stainless steel tubes.
Innovation Solution
A coaxially configured TEC/TEF cable design where optical fibers are encased in a welded metal tube, with an electrically conducting layer surrounding the metal tube, an insulating layer, and an outer metal tube, allowing for a reduced diameter of no more than 4 mm while providing sufficient current carrying capacity for coiled tubing drilling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a TEC/TEF cable with both optical fibers and electrical conductors is used, then current carrying capacity is improved, but cable diameter increases beyond 4 mm
Solution Approach 1:
The patent applies nesting by placing the optical fiber inside the stainless steel tube, then wrapping the copper conductor around the tube in the helical space. This nested arrangement allows both the fiber and conductor to share the same radial space, enabling the cable to fit within 4 mm diameter while providing sufficient current carrying capacity through the copper conductor.
Solution Approach 2:
The patent transitions from a traditional side-by-side arrangement of fiber and conductor to a three-dimensional configuration where the copper conductor wraps helically around the central tube. This dimensional change utilizes the available space more efficiently, allowing the cable to maintain a compact diameter while accommodating both optical and electrical functions.
2Volume of moving object
If the stainless steel tube in a TEF cable is used as the conductor, then cable diameter is reduced, but electrical resistance increases due to insufficient current carrying capacity
Solution Approach 1:
The patent creates a composite conductor system combining the stainless steel tube (providing mechanical strength and optical fiber protection) with a copper conductor (providing low electrical resistance). The copper is wrapped around the steel tube, forming a hybrid structure that leverages the advantages of both materials: the steel maintains cable integrity and protects the fiber, while the copper ensures sufficient current carrying capacity.
Solution Approach 2:
The stainless steel tube serves multiple functions simultaneously: it acts as a protective sheath for the optical fiber, provides mechanical strength to the cable, and serves as a structural core around which the copper conductor is wrapped. This multi-functionality eliminates the need for separate protective tubes and conductors, reducing overall cable diameter while maintaining electrical performance.
Data Source
Figure 1
AI summary
An optical/electrical cable for downhole environments includes a plurality of optical fibers disposed within an interior metal tube. An electrically conducting layer surrounds the interior metal tube, an insulation layer surrounds and contacts the electrically conducting layer, and an exterior metal tube surrounds and contacts the insulation layer.