Turned-Down Casing Tubular for Centralizer Clearance Control
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Solution Overview
Problem
Bow-spring centralizers used in oilfield tubulars can be damaged when passing through restrictions with small clearances, reducing their ability to maintain annular standoff, and the tolerance in outer diameters of tubulars complicates precise clearance determination.
Innovation Solution
A method involving measuring the outer diameter surface of tubulars at multiple planes, simulating a cutting process to create a turned-down region with a maximum diameter and minimum thickness, and positioning a downhole tool within this region to accommodate centralizers and maintain structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bow-spring centralizers are used to maintain concentricity in wellbores with restrictions, then the ability to provide annular standoff is improved, but the centralizers may be damaged when passing through small clearances
Solution Approach 1:
The centralizer is divided into multiple expandable ribs or blades that can independently flex and collapse. This segmentation allows the centralizer to compress radially when encountering restrictions, with each segment absorbing impact forces, thereby preventing damage while maintaining the ability to provide standoff after passing through the restriction.
Solution Approach 2:
The centralizer employs dynamic expandable and collapsible elements that can change their radial profile in response to wellbore conditions. The structure transitions from an expanded state (for providing standoff) to a compressed state (for passing through restrictions), enabling it to adapt to varying clearance conditions without damage.
2Ease of manufacture
If tubular outer diameter tolerance is accommodated, then manufacturing flexibility is improved, but precise clearance determination becomes difficult
Solution Approach 1:
The centralizer design incorporates adjustable parameters such as expandable rib configurations and flexible materials that can adapt to a range of outer diameter tolerances. By changing the physical state or configuration parameters of the centralizer components, the system can accommodate manufacturing variations while maintaining functional performance.
Solution Approach 2:
The system incorporates measurement and feedback mechanisms that detect the actual outer diameter of the tubular and adjust the centralizer expansion accordingly. This feedback loop enables precise clearance determination despite tolerance variations, allowing the centralizer to optimize its standoff distance based on real-time measurements.
Data Source
AI summary
A downhole tool assembly includes a tubular having a turned-down region and a raised region extending axially away from the turned-down region. An inner diameter surface of the tubular in the turned-down region has a higher ellipticity than an outer diameter surface in the turned-down region. The outer diameter surface in the turned-down region defines a first center that is offset from a second center defined by the outer diameter surface of the tubular away from the turned-down region. The downhole tool assembly also includes a cylindrical tool disposed at least partially in the turned-down region.