Subsea Fluid Storage Unit With Variable-Volume Tank and Floodable Gap
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Solution Overview
Problem
The challenge of maintaining heat in fluids stored underwater, preventing leakage, and managing pressure differentials in subsea storage facilities, particularly in deep waters, is significant for marginal oil fields due to the high costs and technical complexities involved in thermal insulation and pressure management of subsea storage units.
Innovation Solution
A modular subsea fluid storage unit with a variable-volume inner tank, a rigid top panel, and a flexible peripheral wall, surrounded by a housing part that includes a floodable gap for thermal insulation and a double barrier against leakage, allowing for easy assembly and maintenance without heavy-lift vessels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If wet thermal insulation is used to maintain oil temperature in subsea pipelines, then the oil temperature can be maintained above the critical threshold, but the cost becomes inordinately expensive for long pipelines
Solution Approach 1:
The patent extracts the thermal insulation function from the pipeline itself and relocates it to a dedicated subsea storage unit. The storage unit is equipped with thermal insulation and heating systems that maintain oil temperature independently, allowing the pipeline to operate without expensive wet thermal insulation over long distances.
Solution Approach 2:
The subsea storage unit acts as an intermediary between the pipeline and the topside installation. It provides thermal management services to the oil, allowing the pipeline to transport oil without requiring expensive thermal insulation, while the storage unit maintains the necessary temperature through its own insulation and heating systems.
2Stress or pressure
If rigid subsea storage tanks are used in deep water, then they can withstand hydrostatic pressure, but they become impractically large and heavy
Solution Approach 1:
The patent employs a flexible bladder or membrane as the storage tank structure. This flexible shell can withstand hydrostatic pressure through its ability to deform and redistribute stress, eliminating the need for heavy rigid construction. The thin-film bladder provides the necessary pressure resistance while maintaining a compact and lightweight design suitable for deep water deployment.
Solution Approach 2:
The storage tank transitions from a static rigid structure to a dynamic flexible structure. The bladder can expand and contract as oil is stored or withdrawn, and can deform to distribute hydrostatic pressure evenly across its surface. This dynamic behavior allows the tank to withstand deep water pressures without requiring excessive weight or size.
3Reliability
If a flexible bladder is used to balance internal and external pressures, then the tank can be compact and lightweight, but fine pressure management is required to avoid bursting
Solution Approach 1:
The patent implements a nested double-barrier system where an inner bladder is placed within an outer containment structure. The inner bladder provides the flexible pressure-balanced storage, while the outer structure provides additional containment and protection. This nested arrangement creates redundant barriers against leakage without significantly increasing overall system complexity.
Solution Approach 2:
The double-barrier system provides beforehand cushioning against potential failures. If the inner bladder fails, the outer containment structure prevents leakage into the marine environment. This pre-established protective layer ensures reliability without requiring complex active pressure management systems during operation.
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 solution provides effective thermal insulation, prevents leakage into the marine environment, and ensures pressure compensation, reducing installation costs and operational complexity while maintaining fluid integrity and safety.
Implementation Method 1
a side wall that surrounds and is spaced from the peripheral wall of the inner tank in a horizontal direction to define a floodable gap that surrounds the tank
Data Source
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AI summary
A modular subsea fluid storage unit comprises a variable-volume inner tank having a rigid top panel and a peripheral wall that is flexible by virtue of concertina formations. The peripheral wall is extensible and retractable vertically while the horizontal width of the tank remains substantially unchanged. A side wall of a lower housing part surrounds and is spaced horizontally from the peripheral wall of the inner tank to define a floodable gap between the peripheral wall and the side wall that surrounds the tank. An upper housing part extends over and is vertically spaced from the top panel of the inner tank and overlaps the side wall to enclose the inner tank. The floodable gap and the upper housing part enhance thermal insulation and trap any fluids that may leak from the inner tank.