Rotary Steerable Mandrel Bending Stress Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing rotary steerable systems for directional drilling face challenges such as internal cyclic bending stresses, limited turn rates, vibration issues, and complexity in field serviceability, particularly when operating in 'point the bit' mode, which can lead to shaft fatigue and increased costs.
Innovation Solution
A steering assembly with a mandrel and housing configuration that includes a deflector device for providing a side force and a tool face assembly for rotating the mandrel, allowing for independent directional control and minimizing bending stresses, featuring a pivot stabilizer sub and a near-bit stabilizer sub connected to the drill bit, enabling operation in both 'push the bit' and 'point the bit' modes with adjustable dogleg severity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a rotary steerable system operates in 'point the bit' mode with a non-rotating housing and bent sub, then directional control is achieved, but internal cyclic bending stresses cause shaft fatigue and reduced reliability
Solution Approach 1:
The system divides the steering function into two independent segments: a non-rotating housing providing lateral force through pads, and a rotating mandrel that can independently rotate relative to the housing. This segmentation allows the mandrel to relieve bending stresses by rotating, while the housing maintains directional control through pad activation, thus resolving the contradiction between directional control and shaft fatigue
Solution Approach 2:
The mandrel is designed with rotational freedom relative to the housing through bearing assemblies, transforming the static bent sub configuration into a dynamic system. The mandrel can rotate to accommodate cyclic bending stresses while the housing remains relatively stationary for directional control, enabling the system to adapt dynamically to operational stresses and prevent shaft fatigue
2Force
If the housing is non-rotating or slowly rotating with pads pushing against the wellbore, then side force is applied for steering, but friction and wear increase device complexity and reduce ease of operation
Solution Approach 1:
The system replaces the conventional mechanical pad-against-wellbore friction interface with a more efficient mechanical leverage system. The pads apply force to the housing, which transfers this force through the mandrel's rotational mechanism to the drill bit, substituting direct friction-based steering with a leveraged force transmission system that reduces operational friction and wear
Solution Approach 2:
The mandrel acts as an intermediary element between the pads and the drill bit. Instead of pads directly pushing the drill bit through friction, the mandrel mediates this force transmission, allowing the pads to apply lateral force to the housing while the mandrel converts this into directional steering with reduced friction and wear on the steering components
3Measurement precision
If a bent sub is used to deflect the shaft for angular change, then directional steering is achieved, but limited turn rates and vibration reduce productivity
Solution Approach 1:
The system replaces the static bent sub with a dynamic mandrel assembly that can rotate independently. This dynamic configuration allows for faster directional changes and higher turn rates while maintaining precise directional steering control, as the mandrel can rapidly adjust its orientation without the mechanical limitations of a fixed bent sub geometry
Solution Approach 2:
The steering function is segmented into the housing (providing lateral force) and the mandrel (providing rotational freedom and directional adjustment). This segmentation allows the mandrel to independently optimize for high-speed directional changes and turn rates, while the housing maintains steering precision through controlled pad activation, resolving the contradiction between steering precision and turn rate productivity
Data Source
AI summary
A steering assembly includes a housing having a longitudinal axis, a mandrel having a front connecting extremity and a rear connecting extremity, the mandrel passing through the housing and arranged in a first position coaxially to the longitudinal axis of the housing, a deflector device configured to exert a side force on the mandrel to offset the front connecting extremity of the mandrel from the longitudinal axis, and a tool face assembly configured to rotate the front connecting extremity of the mandrel in a desired direction.