Three-Part Packoff Assembly for High-Pressure Wellhead Sealing
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Solution Overview
Problem
Existing cup tools for high-pressure mandrels in well stimulation fail to provide a reliable seal in curved or out-of-round tubing and are compromised by low temperature and caustic fluids, leading to seal failure.
Innovation Solution
A three-part packoff assembly comprising an elastomeric cup, a rigid alignment ring, and an elastomeric packoff element, with a gauge ring providing a stable buffer to ensure a high-pressure fluid seal under adverse downhole conditions, including sloped or right-angled shoulders to guide the packoff element into position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single elastomeric cup is used for sealing, then the structure is simple, but the seal fails under adverse conditions (low temperature, caustic fluids, curved tubing)
Solution Approach 1:
The packoff assembly is divided into three distinct parts: an upper elastomeric cup, a middle rigid alignment ring, and a lower elastomeric packoff element. Each component performs a specific function - the upper cup provides initial sealing, the rigid ring maintains geometric stability and alignment in curved tubing, and the lower element ensures pressure-tight sealing. This segmentation allows the system to overcome the limitations of a single elastomeric cup while maintaining reasonable structural complexity.
Solution Approach 2:
The packoff assembly combines materials with different properties: elastomeric materials (flexible, sealable) for the upper and lower elements, and rigid material (geometrically stable, alignment-maintaining) for the middle ring. This composite structure leverages the advantages of each material type - the elastomeric portions provide sealing capability while the rigid portion provides structural stability and alignment, resulting in a packoff assembly that maintains reliability under adverse downhole conditions.
2Reliability
If elastomeric sealing elements are used, then sealing capability is provided, but the materials are compromised by low temperature and caustic fluids leading to seal failure
Solution Approach 1:
The rigid alignment ring is positioned between the two elastomeric sealing elements to protect them from adverse conditions. The rigid ring acts as a protective barrier that shields the elastomeric materials from direct exposure to low temperature and caustic fluids, preventing material degradation before it can occur. This beforehand cushioning approach allows the elastomeric elements to maintain their sealing capability without being compromised by harsh environmental factors.
3Reliability
If a packoff element is expanded under high pressure to seal, then sealing is achieved, but the element may distort in out-of-round or bent tubing
Solution Approach 1:
The rigid alignment ring serves as an intermediary element between the upper and lower elastomeric components. It maintains the geometric alignment and shape of the packoff assembly during expansion under high pressure, preventing distortion in out-of-round or bent tubing. The rigid ring transfers and distributes the expansion forces uniformly, ensuring that the elastomeric elements expand symmetrically and maintain their intended geometry while forming the seal.
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 ensures a reliable high-pressure fluid seal in non-straight or eroded tubing and withstands low temperatures and caustic fluids, preventing seal failure and maintaining integrity during well stimulation.
Implementation Method 1
a cup tool and/or a packoff element that radially expands under high fluid pressures to seal against the inside wall of a production tubing or casing
Implementation Method 2
The cup tool includes a three-part packoff assembly that slides over a cup tool tube from an unset to a set position. The three-part packoff assembly includes an elastomeric cup, a rigid alignment ring located above the elastomeric cup and an elastomeric packoff element located above the rigid alignment ring.
Data Source
AI summary
A cup tool for use with a high-pressure mandrel of a wellhead isolation tool has a three-part packoff assembly that slides over a cup tool tube from an unset position to a set position. The three-part packoff assembly includes an elastomeric cup, a rigid alignment ring located above the elastomeric cup and an elastomeric packoff element located above the rigid alignment ring. The rigid alignment ring helps ensure that the elastomeric cup remains correctly aligned in a casing or tubing that is not straight, is out of round or is washed, and helps ensure that the elastomeric packoff achieves a high-pressure seal in the set position, even under adverse downhole conditions.