Variable Drill String Rotation for Directional Drilling
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Solution Overview
Problem
Conventional directional drilling methods face inefficiencies due to static friction when advancing the drill string, particularly in horizontal or high-angle wells, leading to increased force requirements and potential damage to drill bits, as they often require alternating periods of sliding and rotating, which can result in suboptimal borehole orientation and penetration rates.
Innovation Solution
The method involves continuously rotating the drill string in one direction while varying the angular velocity within each revolution, maintaining similar velocity profiles for each rotation to steer the borehole along a desired trajectory, minimizing the impact of static friction and maintaining effective tool-face orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional directional drilling alternates between sliding and rotating operations, then borehole direction can be controlled, but static friction increases and penetration efficiency decreases
Solution Approach 1:
The patent applies continuous rotation of the drill string throughout the directional drilling process, eliminating the alternating sliding and rotating operations. The control system continuously adjusts the rotational speed and tool-face orientation to maintain both direction control and continuous drilling action, thereby eliminating static friction buildup and improving penetration efficiency while maintaining orientation precision.
2Manufacturing precision
If drill string rotation is stopped during sliding operation to control borehole direction, then orientation accuracy improves, but static friction increases and force requirements increase
Solution Approach 1:
The patent employs dynamic control of drill string rotation by continuously adjusting rotational speed rather than stopping rotation. The control system modulates the rotational speed to achieve the desired tool-face orientation and borehole direction while maintaining continuous motion, thereby reducing static friction and lowering the force requirements compared to conventional sliding operations.
3Productivity
If drill string is continuously rotated at constant speed, then drilling efficiency is maintained, but borehole direction control becomes difficult
Solution Approach 1:
The patent changes the rotational speed parameter dynamically during drilling operations. The control system adjusts the rotational speed of the drill string based on the desired borehole trajectory, slowing down or speeding up rotation to achieve precise directional control while maintaining continuous drilling action. This variable speed control enables both efficient drilling and accurate trajectory management.
4Shape
If alternating sliding and rotating operations are used for directional drilling, then borehole curvature can be achieved, but drill bit overload and damage risk increase
Solution Approach 1:
The patent maintains continuous rotation of the drill string during directional drilling operations, eliminating the repeated stopping and starting associated with alternating sliding and rotating operations. This continuous motion prevents sudden load spikes and shock loads on the drill bit, reducing wear and damage risk while still achieving the desired borehole curvature through controlled variable speed rotation and tool-face orientation adjustments.
Data Source
AI summary
Apparatus and methodology is provided for directional drilling which avoid the effects of static friction between the drill string and the borehole. The drill string is rotated continuously in one direction during rotating drilling and during steering. During steering, the rotary speed of the drill string is varied within a revolution and substantially similarly for each of a plurality of subsequent revolutions. The drill string is rotated very slowly when oriented at or near the desired orientation to achieve the desired change in direction and then rotated much faster during the balance of each revolution. This angular velocity profile results in drilling at or near a desired orientation for a high percentage of the time it takes for each revolution. Changes in an effective tool-face orientation can be effected by shifting the phase of the velocity profile.