Nested Drilling Riser System with Independent Tensioning
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Solution Overview
Problem
Offshore oil and gas drilling platforms face challenges in maintaining riser integrity and meeting dual barrier requirements due to environmental conditions and riser length, weight, and thermal expansion differences between external and internal risers in deep water environments.
Innovation Solution
A nested riser system with independent tension devices for both external and internal risers, where the external riser is buoyantly supported and the internal riser is dynamically tensioned, ensuring continuous tension and fluid integrity while accommodating thermal expansion and platform movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single riser system is used to connect subsea wellhead to platform, then the system is simple, but it cannot meet dual barrier requirements and maintain fluid integrity in deep water environments
Solution Approach 1:
The patent implements a nested riser system where an internal riser is positioned inside an external riser. Both risers extend from the subsea wellhead to the platform, creating a dual-barrier configuration that maintains fluid integrity while managing the complexity through integrated nesting rather than separate independent systems.
Solution Approach 2:
The riser system is segmented into distinct functional components: an external riser for structural support and buoyancy, and an internal riser for fluid conveyance. This segmentation allows each component to be optimized for its specific function while together they satisfy the dual barrier requirement.
2Length of moving object
If riser length is increased to reach deep water deposits, then drilling capability is improved, but riser weight increases causing buckling and stress problems
Solution Approach 1:
Buoyancy devices are attached to the external riser to provide upward buoyant force that counteracts the downward gravitational force on the long riser. This reduces the net weight and prevents buckling while allowing the riser to span the deep water distance from platform to subsea wellhead.
3Stability of the object's composition
If platform motion is allowed to accommodate environmental conditions, then platform stability is improved, but riser tension varies causing stress on subsea wellhead
Solution Approach 1:
The riser tensioning system is made dynamic through the use of buoyancy devices that can adjust their buoyant force and dampers that can adjust their damping characteristics. This allows the system to adapt to varying platform motions and environmental conditions while maintaining consistent riser tension and preventing excessive stress on the subsea wellhead.
4Duration of action of stationary object
If thermal expansion is accommodated in deep water environments, then riser durability is improved, but differential expansion between external and internal risers causes stress
Solution Approach 1:
Different sections of the nested riser system are designed with different thermal properties. The external riser, exposed to cold seawater, has insulation and material properties optimized for cold environments, while the internal riser, carrying hot drilling fluid, is designed to withstand high temperatures. This local differentiation of thermal properties allows each component to handle its specific thermal environment, reducing differential thermal stress.
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 nested riser system effectively maintains riser integrity and meets dual barrier requirements by providing independent tensioning and fluid management, reducing stress and buckling risks in high-temperature, deep-water environments.
Implementation Method 1
buoyancy devices to independently support a riser
Implementation Method 2
A plurality of active hydraulic cylinders with pneumatic accumulators is connected between the platform and the riser to provide and maintain the necessary riser tension
Implementation Method 3
pneumatic accumulators is connected between the platform and the riser to provide and maintain the necessary riser tension
Implementation Method 4
dampers between the platform and the riser to reduce the amount of motion the platform undergoes relative to the riser
Data Source
AI summary
An offshore well system for a subsea well includes an internal riser tension device configured to apply tension to an internal riser and an external riser tension device configured to apply tension to an external riser such that the external riser is supported at least partially independent of the internal riser tension device.