Offset-Shaft Sticking Fixture for Drill Collar Filter Cake Testing
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Solution Overview
Problem
Differential sticking occurs when drill collars embed into the filter cake in high angle and horizontal wells, causing large side forces that exceed mechanical specifications and make it impossible to recover the drill string.
Innovation Solution
A test fixture with a cylindrical screen filter and offset shaft generates a filter cake around a test piece, simulating downhole conditions, and uses a roto-linear actuator to dislodge the test piece by measuring the forces required to break free from the filter cake.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If drill collars are used in high angle and horizontal wells, then the drill string can be positioned correctly, but the drill collars embed into the filter cake causing differential sticking that exceeds mechanical specifications
Solution Approach 1:
The test fixture performs preliminary testing of drill collar components under simulated downhole conditions before actual field deployment. By pre-characterizing the sticking forces and embedment behavior of specific drill collar designs, operators can select components that are less prone to differential sticking in high angle wells, thereby preventing the harmful side forces before they occur.
Solution Approach 2:
The test fixture creates a simplified copy of downhole conditions using a scale model drill collar (test piece) embedded in an artificial filter cake within a controlled chamber. This copy allows measurement of differential sticking forces without risking damage to actual drill strings in the wellbore, enabling safe evaluation of component performance under realistic but controlled conditions.
2Loss of substance
If the filter cake thickness increases to prevent fluid losses, then fluid loss is reduced, but the embedding force into the drill collar increases causing greater sticking forces
Solution Approach 1:
The test fixture applies excessive filter cake thickness beyond what would normally form in the wellbore to fully characterize the maximum sticking forces. By testing with thicker than typical filter cakes, the fixture captures the worst-case scenario embedding forces, providing data that helps operators understand the trade-off between fluid loss control and sticking risk.
Solution Approach 2:
The test fixture systematically varies parameters including filter cake thickness, drilling fluid composition, and confining pressure to map out the relationship between these variables and differential sticking forces. By changing these parameters in controlled steps, the fixture identifies threshold values where the benefit of reduced fluid loss begins to be offset by excessive sticking forces.
3Measurement precision
If in-situ testing of drill collars is performed, then accurate sticking force measurements are obtained, but the testing process is time-consuming and requires complex downhole equipment
Solution Approach 1:
The test fixture uses scaled-down model drill collars that replicate the critical geometric and mechanical properties of full-size components. These models allow rapid testing in a laboratory setting, producing accurate sticking force measurements without the time delays associated with deploying and retrieving specialized downhole testing equipment.
Solution Approach 2:
The test fixture replaces complex downhole mechanical testing systems with a simplified laboratory apparatus that uses a rotating chamber and artificial filter cake to simulate embedding conditions. This substitution maintains measurement accuracy for differential sticking forces while dramatically reducing testing time and eliminating the need for complex in-well equipment deployment.
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 test fixture accurately determines the differential sticking forces by simulating downhole conditions, allowing for the efficient measurement and analysis of forces required to dislodge stuck drill components.
Implementation Method 1
The mesh surface generates a filter cake when particle-entrained fluid is supplied through the mesh surface and the particulate is retained on the mesh surface
Implementation Method 2
The test fixture includes a bearing that decouples rotational motion of the offset shaft from the end cap
Data Source
AI summary
A test fixture includes a cylindrical main body extending in a longitudinal direction that receives a test piece. The main body includes a cylindrical screen filter with a mesh surface that extends in along a longitudinal axis coincident with an axis of the main body. The mesh surface generates a filter cake when particle-entrained fluid is supplied through the mesh surface and the particulate is retained on the mesh surface. The main body also includes an offset shaft that extends in the longitudinal direction along an offset axis that is offset from the axis of the main body, and the test piece extends through the offset shaft and the interior of the screen filter. The main body further includes a bearing that decouples rotational motion of the offset shaft from the end cap. Additionally, the test fixture includes an actuator that dislodges the test piece from the filter cake, a computer that determines the dislodging force, and a reservoir pump that pumps the particle-entrained fluid into the screen filter. When the alignment wheel is actuated, the offset shaft forces the test piece to move from a first position where a longitudinal axis of the test piece is coincident to the longitudinal axis of the screen filter to a second position in which the axes are offset.