Offshore Riser Annular Tensioner for Thermal Expansion
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Solution Overview
Problem
Offshore drilling platforms face challenges with riser stability due to thermal expansion and movement caused by environmental conditions, leading to potential buckling and increased stress on subsea wellheads, especially in deep water and high temperature formations.
Innovation Solution
A system utilizing an annular tensioner with castellated gathering fingers and a dynamic seal to maintain tension in the riser, allowing for relative movement between the inner and outer tubing, and independent tensioning of external and internal risers to prevent buckling and accommodate thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the riser is tensioned to prevent buckling under its own weight, then the riser stability is improved, but the stress on the subsea wellhead increases
Solution Approach 1:
The riser system is divided into multiple segments: the riser itself, the annular tensioner, the production tubing, and the buoyancy device. Each segment can be independently tensioned and controlled, allowing the riser to be stabilized without concentrating all tension forces at the subsea wellhead. The annular tensioner acts as an intermediate segment that distributes tension forces.
Solution Approach 2:
The annular tensioner serves as an intermediary device between the riser and the production tubing. It provides a mechanical interface that allows independent tensioning of the riser while accommodating the movement of the production tubing due to thermal expansion, thereby stabilizing the riser without transmitting excessive stress to the subsea wellhead.
2Stability of the object's composition
If the riser is made rigid to maintain stability, then the riser stability is improved, but the ability to accommodate thermal expansion decreases
Solution Approach 1:
The system employs dynamic elements that allow for movement and adjustment. The production tubing is dynamically supported within the annular tensioner, enabling it to expand and contract freely in response to temperature changes while the outer riser maintains its structural stability. This dynamic configuration allows both rigidity for stability and flexibility for thermal accommodation.
Solution Approach 2:
The production tubing is nested within the annular tensioner, which itself is positioned within the riser. This nested configuration allows the inner production tubing to move independently (accommodating thermal expansion) while the outer riser structure provides overall stability. The nested design enables differential movement between the inner and outer components.
3Force
If buoyancy devices are used to support the riser, then the tensioner capacity needs are reduced, but the platform movement isolation effectiveness decreases
Solution Approach 1:
The buoyancy device utilizes pneumatic or hydraulic principles to provide upward force support for the riser. By incorporating a flexible membrane or bladder within the buoyancy device, the system can accommodate platform heave motion while maintaining buoyant support, thus reducing tensioner capacity requirements without compromising movement isolation.
4Reliability
If the production tubing is fixed relative to the riser, then the fluid integrity is maintained, but the thermal expansion causes buckling
Solution Approach 1:
The annular tensioner incorporates flexible sealing elements and thin film membranes that maintain fluid integrity while allowing relative movement between the production tubing and the riser. These flexible components create dynamic seals that accommodate thermal expansion and contraction of the production tubing without compromising the fluid barrier, preventing buckling while maintaining integrity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively reduces buoyancy and tensioner capacity needs, maintains riser tension, and prevents buckling, while allowing for monitoring of seals and control lines from the floating structure deck, enhancing stability and fluid integrity in high-temperature environments.
Implementation Method 1
maintain tension in the riser
Implementation Method 2
dynamic seal to maintain tension in the riser
Implementation Method 3
thermal expansion, due to the fact that the drilling extends into very high temperature formations
Data Source
AI summary
The riser system of the present invention includes an external production riser for floating structures with interfaces to the dry and subsea wellheads, internal tieback riser with a special lower overshot/slipping connector for elevated temperatures. The seals can be metallic and/or non-metallic dynamic seals. Special centralizing pipe connectors and a special subsea wellhead tubing hanger are also included. This riser system avoids the penalty of pipe within pipe differential thermal growth and the resulting unwanted effects on the floating structure. This is accomplished by allowing an overshot sealing slipping connector to swallow an expanding polished rod as thermal conditions cause pipe elongation axially. When elevated temperatures fall to ambient the opposite occurs as the pipe shrinks axially. Alternatively, a system is possible where a two pipe drilling riser is needed. The internal pipe in this case would be an inner riser rather than a tubing string.