Downhole Centraliser Stiffness Segmentation for Bore Restrictions
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Solution Overview
Problem
Centralisers used in boreholes face challenges in maintaining casing coaxiality, especially in deviated or horizontal bores, due to deformation of spring bow portions, which affects the consistency of the cement sheath thickness and increases the difficulty in running the casing through restrictions.
Innovation Solution
A centraliser design with end portions being more flexible and intermediate portions being more rigid, allowing for deformation to pass through bore restrictions while ensuring recovery to the original diameter, featuring curved sections and connectors to distribute load and reduce stress, and potentially incorporating friction-reducing coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the stiffness of the spring bow portions is increased to maintain casing coaxiality in deviated or horizontal bores, then the restoring force is improved, but the starting force and running force increase making it more difficult to pass through bore restrictions
Solution Approach 1:
The spring bow portion is divided into multiple segments (first, second, and third bow portions) with different stiffness characteristics. The first and third bow portions have higher stiffness to provide restoring force, while the second intermediate bow portion has lower stiffness to facilitate passage through restrictions, allowing the centraliser to navigate bore restrictions more easily while maintaining casing coaxiality after installation
Solution Approach 2:
Different sections of the spring bow portion are assigned different local properties: the end portions (first and third bow portions) are made stiffer to provide restoring force for maintaining casing position, while the intermediate portion (second bow portion) is made more flexible to allow deformation during passage through restrictions. This local differentiation resolves the contradiction between needing high restoring force and ease of passage through restrictions
2Ease of operation
If the spring bow portions are made more flexible to ease passage through restrictions, then the running force is reduced, but the restoring force decreases making it more difficult to maintain casing coaxiality
Solution Approach 1:
The spring bow portion is segmented into multiple sections with varying stiffness. The intermediate second bow portion is made more flexible with a larger radius of curvature to facilitate passage through restrictions, while the first and third bow portions near the collars maintain higher stiffness to ensure adequate restoring force for maintaining casing coaxiality after installation
Solution Approach 2:
The spring bow portion exhibits local quality variations where the intermediate section has different mechanical properties (lower stiffness, larger radius of curvature) compared to the end sections. This allows the intermediate portion to deform easily during restriction passage while the end portions provide the necessary restoring force to maintain casing position in the bore
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 design enables the centraliser to maintain the casing coaxial with the bore, ensuring consistent cement sheath thickness and facilitating easier passage through bore restrictions by controlling deformation and reducing friction, thereby improving the running and restoring forces.
Implementation Method 1
The spring bow portions may be deflected radially inwards to permit a casing string carrying such centralisers to pass through bore restrictions. The spring bow portions must also recover to a larger diameter configuration after passing through the restriction.
Implementation Method 2
The primary roles of a centraliser are to facilitate running of the casing string to the desired depth in the bore and then to provide a sufficient force, sometimes referred to as the restoring force, to maintain the casing coaxial with the bore.
Data Source
Figure 1~2
Figure 3~4b
Figure 5~7
AI summary
A centraliser (112) includes a number of members (118) extending between two collars (120) for mounting the centraliser (112) on a casing (110). The members (118) are configured to contact a wall (115) of the bore (114) and centraliser the casing (110) in the bore (114).The members (118) are radially moveable between the casing (110) and the bore wall (115). The members (118) further include an intermediate portion (119) and end portions (221), the end portions (221) being relatively more flexible than the intermediate portion (119).