Subsea Flexible Bladder Tank for Offshore Liquid Storage
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Solution Overview
Problem
Offshore oil and gas production facilities face challenges in storing large volumes of liquids for enhanced oil recovery due to space and weight constraints, and existing solutions like FPSO vessels are costly and sensitive to weather conditions.
Innovation Solution
A subsea storage tank system featuring a protective enclosure with inner and outer flexible bladders, allowing for separate liquid storage and recirculation, connected to conduits and pumps for efficient liquid management and distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If large volumes of liquid are stored on offshore platforms, then chemical injection operations can be sustained, but the platforms cannot accommodate the space nor the weight associated with storage of such volumes
Solution Approach 1:
The storage system transitions from surface-level platform storage to subsea floor storage, utilizing the vertical dimension and underwater space. The protective enclosure is positioned on the seafloor, allowing large volume storage without occupying platform deck space, thus resolving the contradiction between storage volume and platform area.
Solution Approach 2:
The system employs nested flexible bladders where an inner flexible bladder containing the inner liquid is placed within an outer flexible bladder. The space between the inner and outer bladders contains an outer liquid, creating a nested configuration that maximizes storage efficiency within the protective enclosure while accommodating thermal management requirements.
2Quantity of substance
If large volumes of liquid are stored on offshore platforms, then chemical injection operations can be sustained, but the weight associated with storage of such volumes cannot be accommodated
Solution Approach 1:
The system uses flexible bladders (inner and outer) instead of rigid metal tanks. These flexible membranes provide the necessary containment while being significantly lighter than equivalent rigid steel structures. The flexible bladders can be inflated or deflated as needed, and their weight is negligible compared to the liquid they contain, resolving the weight accommodation issue.
Solution Approach 2:
By moving storage from platform to subsea floor, the weight burden is transferred from the platform structure to the seafloor environment. The protective enclosure and its contents rest on the seafloor, eliminating the need for the platform to support this weight, thus resolving the contradiction between storage volume and platform weight capacity.
3Quantity of substance
If FPSO vessels are used to supply chemicals, then chemical storage is possible, but they are expensive to operate and can be sensitive to weather and ocean conditions
Solution Approach 1:
The subsea storage system operates autonomously once installed. The recirculation pump circulates outer liquid through heat exchangers to maintain temperature, and the system can be refilled through conduits from surface vessels without requiring the vessel to remain on station. This eliminates the continuous operational costs and weather sensitivity associated with FPSO vessels, as the storage system serves itself and can be periodically replenished.
Solution Approach 2:
The invention extracts the storage function from the FPSO vessel concept and places it permanently on the subsea floor. This separates the storage function from the supply function - the storage system remains stationary and autonomous on the seafloor, while surface vessels only need to perform periodic refilling operations through conduits, eliminating the need for expensive FPSO-style continuous supply operations.
4Temperature
If the inner flexible bladder is circulated to maintain temperature, then thermal management is improved, but additional system complexity is introduced
Solution Approach 1:
The outer liquid circulation system serves multiple functions: it acts as a thermal management system by circulating liquid through heat exchangers to heat or cool the inner liquid, and it also provides a barrier between the inner liquid and the external environment. The recirculation pump and heat exchanger infrastructure can potentially serve other thermal management needs in the subsea environment, reducing the relative complexity burden.
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
Enables cost-effective, practical storage and management of large liquid volumes on the seafloor, reducing operational costs and environmental risks while minimizing weight and space requirements.
Implementation Method 1
The storage tank further includes a recirculation loop including a pump for circulating the outer liquid in the space between the inner flexible bladder and the outer flexible bladder
Data Source
AI summary
A storage tank for storing liquids on the seafloor in a subsea environment is disclosed. The storage tank includes a protective enclosure having a removable cover. The storage tank has at least one compartment therein within which is a container including an outer flexible bladder and an inner flexible bladder within the outer flexible bladder. The inner flexible bladder is capable of containing an inner liquid. The space between the inner flexible bladder and the outer flexible bladder is capable of containing an outer liquid. The inner flexible bladder has a liquid inlet capable of connecting to a source of the inner liquid. The inner flexible bladder has a liquid outlet capable of connecting to a line for conveying the inner liquid to a desired location. The storage tank further includes a recirculation loop for circulating the outer liquid in the space between the inner flexible bladder and the outer flexible bladder. A system for managing liquids in an offshore environment is disclosed, the system using the storage tank, a first conduit connected to the inner flexible bladder liquid inlet of the storage tank for supplying the inner liquid from a topside location, a second conduit connected to the inner flexible bladder liquid outlet, and a pump connected to the second conduit for pumping the inner liquid to a desired pressure for conveying the inner liquid to a desired location.