Subsea Riser Installation Using Submerged Pulling Buoy
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Solution Overview
Problem
The installation of subsea risers for hydrocarbon transportation is challenging due to deep-sea operations, where guiding the connecting end to the seabed installation is difficult, and existing methods are prone to damage from oscillatory movements caused by waves and currents, and the suspension system is at risk of failure under varying tensile forces.
Innovation Solution
A method involving a submerged pulling buoy attached to the pulling cable, which applies additional tensile forces to the suspension line, allowing the float and pipe to be lowered and connected to the seabed installation while minimizing the impact of surface disturbances, using a gaseous fluid to compensate for weight and additional forces, and anchoring the buoy to the seabed to stabilize the assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the connecting end is driven toward the seabed installation using pulling cables from a surface ship, then the connection between the pipe and seabed installation is achieved, but the male element strikes the female element violently causing damage due to oscillatory movements from waves and currents
Solution Approach 1:
A submerged buoy acts as an intermediary device between the surface ship and the connecting end. The buoy is positioned near the seabed installation and connected via pulling cables, serving as a stable intermediate point that is less affected by surface waves. This mediator allows the connecting end to be guided gently toward the female element without violent oscillations from surface disturbances.
Solution Approach 2:
The submerged buoy provides a counterbalancing effect to the oscillatory movements caused by waves and currents. By positioning the buoy at a depth where it is less affected by surface disturbances and using it as the anchor point for pulling cables, the system counteracts the harmful oscillations that would otherwise be transmitted directly to the connecting end during the connection process.
2Ease of operation
If the float is held by a suspension line from a surface vessel, then the float and pipe can be submerged and positioned vertically, but the suspension line experiences considerable tensile forces that may cause failure when the surface vessel moves due to waves
Solution Approach 1:
The suspension system is segmented into two independent parts: a first suspension line connecting the surface vessel to the float, and a second suspension line connecting the submerged buoy to the float. This segmentation distributes the tensile forces, so that when the surface vessel moves due to waves, the load is shared between both suspension lines rather than concentrated on one line, reducing the risk of failure.
Solution Approach 2:
The submerged buoy serves as an intermediary that stabilizes the suspension system. By introducing a second suspension line anchored to a buoy that is less affected by surface waves, the system creates a more stable support structure. The buoy acts as a mediator that reduces the impact of surface vessel movements on the overall suspension system, distributing and reducing tensile forces.
3Productivity
If the connecting end is guided toward the seabed installation from the water surface, then the riser can be installed in deep-sea operations, but the process becomes awkward and difficult to control
Solution Approach 1:
The operation is shifted from the surface dimension to the subsurface dimension. Instead of guiding the connecting end from the water surface where wave and current effects are strongest, the submerged buoy is positioned near the seabed installation at a depth where these disturbances are significantly reduced. This dimensional shift to an deeper operational level provides much better control and stability for the connection process.
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
This method stabilizes the connection process, reduces the risk of damage to the connecting end, and ensures the suspension system's integrity by canceling out tensile forces applied to the surface vessel, allowing precise control over the connection and reducing the influence of waves and currents on the submerged components.
Implementation Method 1
a submerged pulling buoy (36) is attached to said pulling cable so as to apply additional tensile forces to said suspension line; next a gaseous fluid is substituted for the water in said float in order to compensate, on the one hand, for the tensile forces corresponding to the weight of said float and of said pipe and, on the other hand, for at least some of the additional tensile forces
Implementation Method 2
a gaseous fluid is substituted for the water in said float in order to compensate, on the one hand, for the tensile forces corresponding to the weight of said float and of said pipe and, on the other hand, for at least some of the additional tensile forces
Data Source
AI summary
A method of installing an underwater riser includes anchoring an installation to the seabed; coupling a tubular pipe to the installation; equipping the installation with a submersible float; submerging the float and the pipe, while the float and the pipe are being held from a surface vessel; a cable and a return device are installed on the seabed installation so that the cable can be connected to the pipe; attaching a submerged hauling buoy to the hauling cable; then removing ballast from the float in order to compensate for the tensile forces corresponding to the weight of the float and the pipe and to some of the load applied to the cable; and finally, anchoring of the hauling buoy to the installation and gradually releasing the float.