Subsea Wellhead Gasket Seal for Riser Motion
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Solution Overview
Problem
Offshore drilling platforms face challenges in maintaining riser integrity and reducing wear on annular seals due to relative motion between risers and wellheads caused by platform movement in harsh marine environments.
Innovation Solution
A dual-riser system with an internal riser tensioned and landed within the wellhead, utilizing a collet and flange assembly with collapsible fingers and a gasket seal to minimize relative motion and prevent wear, and a riser tension system that dynamically adjusts to platform movements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an annular seal is used to seal against the riser, then fluid integrity is maintained, but wear on the seal increases due to relative motion between the riser and wellhead
Solution Approach 1:
The patent employs a dynamic seal system where the seal can move axially within the wellhead to accommodate riser motion. The seal is mounted on a carrier that can slide along the riser, allowing the seal to maintain contact with the riser surface while moving with it, thereby reducing wear and extending service life while maintaining fluid integrity
Solution Approach 2:
The patent introduces a seal carrier as an intermediary component between the fixed wellhead and the moving riser. This carrier absorbs the relative motion through its own movement, allowing the seal to remain engaged with the riser without experiencing excessive wear from direct friction against a stationary surface
2Strength
If the riser is tensioned to prevent buckling, then structural integrity is maintained, but the platform cannot move freely relative to the riser
Solution Approach 1:
The patent implements a dynamic tensioning system where the riser tension can be adjusted in real-time based on platform motion and environmental conditions. The tensioning mechanism includes movable components that allow the system to transition between different tension states, maintaining structural integrity during normal operation while permitting controlled motion during dynamic events
Solution Approach 2:
The patent utilizes variable tension parameters to balance structural integrity and platform adaptability. By dynamically changing the tension level in the riser based on operational conditions, the system maintains sufficient tension to prevent buckling under static loads while allowing greater platform motion flexibility when environmental conditions require it
Data Source
AI summary
An offshore well system for a subsea well. The system includes a floating platform, an external riser and an internal riser nested within the external riser. A external riser tension device tensions the external riser. The drilling system also includes a surface wellhead system that includes a wellhead, a collet, and a flange assembly. The wellhead, collet, and flange assembly are assembled to establish a common bore for receiving the top of the internal riser. A gasket located between the top of the internal riser and an inner shoulder of the flange assembly seals between the wellhead system and the top of the internal riser. The surface wellhead system also retains the internal riser in tension with the wellhead, the internal riser extending above the wellhead into the collet.