Nested Dual Drill Pipe Seal Assembly for Axial Misalignment
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Solution Overview
Problem
Dual drill pipe systems face challenges in maintaining fluid-tight connections and accommodating axial misalignment during assembly and disassembly, leading to potential leakage and pipe sticking issues, especially in highly inclined wellbores.
Innovation Solution
The implementation of a dual drill pipe design with tapered threads and a seal assembly that includes a tube retainer, anti-extrusion rings, and a spiral locking ring to ensure a metal-to-metal seal, allowing for axial misalignment and preventing buckling of the inner tube, while maintaining a pressure-tight connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If extended seal engagement features are used for the inner tube, then sealing reliability is improved, but the ability to accommodate axial misalignment during assembly deteriorates
Solution Approach 1:
The seal assembly is divided into distinct functional segments: a seal ring for fluid tight sealing, anti-extrusion rings for structural support, and a spiral locking ring for alignment. This segmentation allows each component to perform its specific function independently, resolving the contradiction between sealing reliability and misalignment accommodation.
Solution Approach 2:
The seal assembly combines different material properties - the seal ring provides sealing capability while the metal anti-extrusion and locking rings provide structural strength and alignment features. This composite structure enables both reliable sealing and tolerance for axial misalignment during assembly.
2Reliability
If the inner tube is rigidly connected to maintain pressure-tight connection, then sealing is improved, but the risk of buckling during assembly increases
Solution Approach 1:
The anti-extrusion rings are positioned in advance at critical locations on the inner tube to provide structural support before pressure-tight connection is established. This preliminary reinforcement prevents buckling during the assembly process while maintaining the required pressure-tight connection.
3Ease of operation
If conventional thread connections are used for dual drill pipe, then assembly simplicity is maintained, but fluid leakage risk increases
Solution Approach 1:
The sealing function is merged with the connection function by integrating the seal ring and locking mechanisms directly into the thread connection assembly. This allows conventional thread connections to maintain their simplicity while incorporating specialized sealing components to eliminate fluid leakage risks.
Data Source
Figure 1~2B
Figure 3A~4B
Figure 5~6
AI summary
A seal assembly for a nested dual drill pipe includes a drill pipe member, such as a tube or drill pipe segment, having a female seal assembly (18, 118) and a male seal assembly (16A, 116) at the longitudinal ends thereof. The female seal assembly includes a larger internal diameter portion (18E), a taper (18E1) adjacent thereto, and a smaller internal diameter portion (18F) adjacent to the taper. The male seal assembly includes a smaller external diameter portion (16G), a seal area or groove (16F) adjacent thereto, and a larger external diameter portion (16E) adjacent to the seal groove. The smaller internal diameter portion and the larger external diameter portion have diameters selected to enable free longitudinal movement of the male seal assembly into the female seal assembly while limiting axial displacement to maintain a seal ring (38) in the seal area or groove fully energized.