Short Millable Frac Plug with Anti-Rotation Feature
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Solution Overview
Problem
Existing wellbore plugs face issues with uneven stress distribution and difficulty in removal due to binding with drilling bits, leading to long drill-out times and excessive casing wear, necessitating a solution for improved axial load capacity and efficient removal.
Innovation Solution
A drillable frac plug design featuring a mandrel with threads, sealing elements, backup rings, a cone, and a slip with recessed regions to facilitate breaking into segments, along with anti-rotation features and a shearable portion to ensure even stress distribution and easy removal by shearing the connection between the cone and mandrel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the plug is set with a non-centered slip, then the plug can be installed quickly, but the slip elements are not uniformly disposed around the casing wall resulting in uneven stress distribution and reduced axial load capacity
Solution Approach 1:
The slip is designed with an asymmetric geometry featuring a rounded end and a flat end, allowing it to be inserted in a specific orientation. The rounded end leads the insertion while the flat end provides a stopping surface against the cone, ensuring the slip centers itself automatically during installation without requiring precise alignment procedures.
Solution Approach 2:
The slip is pre-formed with recessed regions that concentrate stress during insertion. These recessed regions are strategically positioned to facilitate breaking the slip into segments as it contacts the cone, ensuring uniform distribution of slip elements around the casing wall before the plug is fully set.
2Loss of time
If the plug components are designed to be easily removed by milling, then the removal time is reduced, but the plug components may bind upon the drilling bit and rotate with it within the casing
Solution Approach 1:
The slip is designed to break into multiple segments upon contact with the cone during setting. These segmented slip elements are distributed uniformly around the casing wall, which prevents them from binding together as a single mass during subsequent milling operations, reducing both drill-out time and casing wear.
Solution Approach 2:
The mandrel is designed with a shearable portion made of a material or with a structure that is easier to cut than the rest of the plug components. This localized weakness allows the shearable portion to be quickly milled away without requiring excessive milling time or causing excessive casing wear to the surrounding intact components.
3Length of moving object
If the plug is designed with a short length, then the milling time is greatly reduced, but the plug must still withstand high differential pressure and maintain seal integrity
Solution Approach 1:
The sealing mechanism transitions from relying on axial compression alone to utilizing radial expansion of the elastomeric packing element. By applying axial force that converts to radial outward force against the casing wall, the seal achieves high pressure containment capability within a compact axial length, eliminating the need for long compression distances.
Solution Approach 2:
The plug employs a composite structure combining rigid components (mandrel, cone, backup rings) with a flexible elastomeric packing element. This composite design allows the rigid parts to provide structural support and force transmission while the elastomeric material provides the sealing function, enabling a short overall length while maintaining seal integrity under high differential pressure.
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 design enhances axial load capacity by ensuring uniform slip segment distribution around the casing, reducing the risk of plug movement and improving seal integrity, while allowing for quicker and more efficient removal by shearing the shearable connection, thus minimizing milling time.
Implementation Method 1
a centralizer disposed around the mandrel proximate an upper end of the upper backup ring that, when subjected to an axial force, cause the centralizer to radially expand to force against the casing wall
Implementation Method 2
the slip moves up on the tapered surface of the cone and breaks apart to form a number of individual slip elements, and the slip elements are driven outwardly, away from the mandrel, and thus engages the casing wall
Implementation Method 3
The axial compression of the packing element causes the packing element to expand radially against the well casing creating a sealing barrier that isolate a portion of the well
Data Source
AI summary
A short millable plug includes a mandrel, an upper backup ring and a lower backup ring, a cone, a slip that can be expand and engage a casing, a plurality of sealing elements that creates a seal between the mandrel and the casing, a centralizer that can radially expand to force against the casing wall, a mill-out anti-rotation feature at the middle of the mandrel which is exposed once the plug is set. The centralizer can keep the plug in the center of the casing and each individual slip segments of the slip has the same distance to the casing wall during setting and operation. The mill-out anti-rotation feature can reduce relative rotation between the plug and the casing while reduces the length of the plug.