Gap Sub Assembly with Helical Grooves for Torsional Strength
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Solution Overview
Problem
Existing gap sub assemblies for directional drilling fail to withstand extreme torsional, compressive, and bending forces while maintaining electrical isolation, leading to connection failures and high manufacturing costs.
Innovation Solution
A gap sub assembly featuring a cylindrical mandrel and housing with staggered axial sections and non-overlapping right- and left-handed helical grooves, filled with an electrically isolating medium that provides mechanical strength and resistance to axial and torsional forces without requiring threading or rotation during assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional gap sub assemblies are used to electrically insulate the upper and lower sections of the drill string, then electrical isolation is achieved, but the assembly fails to withstand extreme torsional, compressive, and bending forces during directional drilling
Solution Approach 1:
The gap sub assembly employs a composite structure combining a mandrel, housing, and electrically isolating medium (such as epoxy or polymer material). This composite design allows the assembly to simultaneously achieve electrical isolation properties from the nonconductive medium and mechanical strength from the structural components, resolving the contradiction between electrical insulation and mechanical durability under extreme drilling forces.
Solution Approach 2:
The gap sub assembly is divided into distinct segments: a mandrel portion, a housing portion, and an electrically isolating medium filling the gap between them. This segmentation allows each component to be optimized independently - the mandrel and housing provide structural strength while the isolating medium provides electrical insulation, enabling the assembly to withstand both mechanical loads and maintain electrical isolation reliability.
2Strength
If complex gap sub designs are implemented to withstand extreme forces, then mechanical strength is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The assembly is segmented into a mandrel, housing, and isolating medium, allowing each component to be manufactured separately using standard drilling industry components and simple processes. The mandrel and housing can be produced through conventional machining or forming, and the isolating medium is applied through simple filling and curing operations, significantly reducing manufacturing complexity and cost compared to integrated complex designs.
Solution Approach 2:
The mandrel and housing portions can be designed as universal components that interface with standard drill string connections, allowing the same basic assembly design to be used across different drilling applications. This multi-functionality reduces the need for custom-manufactured parts and simplifies the manufacturing process while maintaining the required mechanical strength.
3Reliability
If conventional gap sub assemblies are used, then electrical isolation is maintained, but connection failures occur at the weakest point under extreme torsional forces up to 80,000 lb-ft
Solution Approach 1:
The composite structure distributes mechanical stresses across multiple components (mandrel, housing, and isolating medium) rather than concentrating them at a single weakest point. The electrically isolating medium acts as a bonding agent that transfers and distributes torsional, compressive, and bending loads throughout the assembly, preventing connection failures while maintaining electrical isolation without requiring complex reinforcement structures.
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 effectively withstands torsional forces up to 80,000 lb-ft and axial forces, while maintaining electrical isolation, and simplifies deployment with a cost-effective manufacturing process.
Implementation Method 1
an electrically isolating medium filling the gap between the housing and the mandrel, the electrically isolating medium mechanically coupling the housing and the mandrel while maintaining electrical isolation between the housing and the mandrel
Implementation Method 2
a generally cylindrical housing having an interior connecting surface including right- and left-handed helical grooves; a generally cylindrical mandrel having an outer connecting surface inserted into the housing to form a gap between the interior surface of the housing and the outer surface of the mandrel
Data Source
AI summary
An improved gap sub assembly that can withstand the rigors of directional drilling, while still being cost effective and easy to deploy at the drill site. Embodiments can be assembled by sliding a mandrel into a housing without any threading or clocking, filling the gap between the housing and mandrel with an electrically isolating material, and curing the electrically isolating material to mechanically couple the housing and mandrel. In some embodiments, the interior surface of the housing and the outer surface of the mandrel comprise a plurality of complimentary axial sections having staggered diameters so that a constant dielectric gap is maintained. In some embodiments, the interior surface of the housing and the outer surface of the mandrel comprise non-overlapping right- and/or left-handed helical grooves that, when filled with a cured electrically insulating material, forms a complex 3D shear resistance mechanism optimized to resist torsion or twisting.