Drill String Driver Control for Stick-Slip Reduction
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Solution Overview
Problem
Drill strings experience stick-slip motion and resulting rotational waves during drilling operations, leading to reduced penetration rates, bit wear, and equipment damage due to frictional interactions and varying rotational speeds along the drill string.
Innovation Solution
A control system incorporating a processor and memory with a stick-slip algorithm that receives numerical parameters to determine control commands for the driver, reducing rotational waves by varying the rotational speed and torque of the drill string.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If constant rotational speed is applied at the surface driver, then the upper end of the drill string rotates smoothly, but stick-slip motion occurs at the drill bit causing rotational waves and equipment damage
Solution Approach 1:
The control system applies periodic variations to the rotational speed command signal at frequencies corresponding to the drill string's natural frequencies. This periodic action creates controlled vibrations that prevent stick-slip motion by keeping the drill bit in continuous contact with the formation, thereby eliminating the harmful stick-slip cycles while maintaining stable overall rotation
Solution Approach 2:
The system dynamically changes the rotational speed parameter by superimposing vibrational components on the base rotational speed command. The control system adjusts the magnitude and frequency of these speed variations based on real-time feedback from accelerometers and rate sensors, transforming the constant speed regime into a controlled variable speed regime that prevents stick-slip
2Productivity
If rotational waves are allowed to propagate along the drill string, then the drill string can accommodate dynamic loading, but this causes bit wear, reduced penetration rate, and equipment damage
Solution Approach 1:
The control system converts the harmful rotational waves and vibrations into beneficial controlled vibrations. By using feedback from accelerometers to detect natural frequencies and then applying counter-phase vibrations through the driver, the system transforms potentially damaging random vibrations into controlled, beneficial oscillations that enhance rock fragmentation and penetration while reducing bit wear
Solution Approach 2:
The system employs real-time feedback from accelerometers and rate sensors mounted on the drill string to continuously monitor vibrational characteristics. This feedback is processed to identify natural frequencies and stick-slip conditions, and the control system adjusts the rotational speed command accordingly, creating a closed-loop control that actively suppresses harmful vibrations while maintaining productive drilling
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 system effectively reduces the amplitude of rotational waves along the drill string, minimizing stick-slip motion and associated damage, thereby improving drilling efficiency and equipment longevity.
Implementation Method 1
rotational waves travelling along the drill string
Implementation Method 2
frictional interactions with the bottom and sidewalls of the wellbore being drilled
Data Source
AI summary
Apparatus and methods for optimizing a stick-slip algorithm for controlling a driver of a drill string. A method may include commencing operation of a control system for controlling the driver. The control system may have a processor and a memory storing a computer program code, which may include the stick-slip algorithm. The operating control system may receive a plurality of different numerical parameters, and for each of the different numerical parameters, incorporate the numerical parameter into the stick-slip algorithm and execute the stick-slip algorithm to determine a control command that causes the driver to rotate the drill string to perform drilling operations while reducing amplitude of rotational waves travelling along the drill string.