Subsea Casing Hanger Hook Mechanism for Premature Activation Control
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Solution Overview
Problem
Active casing hangers in subsea wellhead assemblies often experience premature activation due to uneven shear pin loading, leading to costly and time-consuming retraction and re-tripping procedures.
Innovation Solution
A wellhead housing design featuring a conical load shoulder and a centralizing mechanism with a split load ring and centralizer ring, where the centralizer ring's fingers provide a spring effect to centralize the hanger and prevent premature activation by engaging only when the correct location within the wellhead is reached, utilizing shear pins to allow load transfer once proper alignment is achieved.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shear pins are used to prevent premature activation of the activation ring, then reliability is improved, but uneven loading can still cause premature activation leading to loss of time and productivity
Solution Approach 1:
The centralizer ring acts as an intermediary mechanism between the hanger and the activation ring. It provides a controlled interface that ensures proper alignment and distribution of forces, preventing uneven loading on shear pins while maintaining the shear pin safety mechanism. The centralizer ring's fingers engage with the hanger body to centralize it within the housing, ensuring the activation ring is only activated at the correct depth.
Solution Approach 2:
The centralizer ring performs preliminary centralizing action before the activation ring is engaged. By establishing proper hanger positioning and load distribution in advance, the system prevents premature activation conditions from developing, ensuring shear pins only fail at the intended activation point when proper alignment is achieved.
2Productivity
If the hanger is lowered quickly to improve productivity, then productivity is improved, but premature activation may occur due to uneven pin loading
Solution Approach 1:
The centralizer ring introduces dynamic adaptability to the system. As the hanger is lowered at varying speeds, the centralizer ring's fingers can adjust their engagement and provide real-time centralizing forces, ensuring that even during rapid installation, the activation ring remains properly aligned and shear pins experience uniform loading until the correct activation depth is reached.
3Device complexity
If a simple activation mechanism is used to reduce device complexity, then device complexity is reduced, but premature activation cannot be prevented
Solution Approach 1:
The activation system is segmented into distinct functional components: the centralizer ring with its segmented fingers that provide centralizing force, the shear pins that provide controlled failure at the correct moment, and the activation ring that executes the activation function. This segmentation allows each component to perform its specific function reliably without requiring complex integration, maintaining simplicity while achieving precise activation control.
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
Prevents premature activation of the casing hanger, reducing the need for costly re-installation by ensuring the load is transferred correctly and efficiently only when the hanger reaches the intended position within the wellhead housing.
Implementation Method 1
shear pins that prevent premature movement of the activation ring
Implementation Method 2
a conical load shoulder machined within its bore. The casing hanger lands on and is supported by the load shoulder
Data Source
AI summary
A subsea wellhead assembly includes a housing with a bore. A hanger is lowered into the housing, the hanger having at least one centralizing finger with a hook for engaging a corresponding hook an activation ring carried by the hanger via a shear pin. A load ring is carried on the hanger and supported initially within a recess formed on the exterior of the hanger. At the correct depth within the housing, coinciding with a shoulder on the inner diameter of the housing, the pin is sheared under the weight of the casing string and the hooks disengage to allow the load ring on the hanger to slide outward and create a path for the casing load to be transferred from the hanger to the hanger load ring, to a housing load ring, and ultimately the housing.