Estimating Downhole RPM Oscillations via Top Drive Torque
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Solution Overview
Problem
Drilling operations face challenges in accurately estimating downhole RPM oscillations due to stick-slip phenomena, which are not effectively addressed by existing technologies, leading to inefficiencies and potential damage to drilling equipment.
Innovation Solution
A method and apparatus that utilize raw surface data from top drive torque and rotational speed, combined with inertia measurements, to estimate drillstring torque and calculate a surface torque oscillation performance index (STOPI), enabling real-time monitoring and mitigation of stick-slip oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If top drive torque readings are used to monitor downhole conditions, then surface measurements are easily obtained, but accurate estimation of downhole RPM oscillations is compromised due to stick-slip phenomena
Solution Approach 1:
The patent introduces an intermediary mathematical model that acts as a mediator between surface torque measurements and downhole RPM oscillations. The model uses the top drive torque readings combined with drillstring mechanical properties (inertia, damping, stiffness) to compute an estimated downhole RPM signal, effectively translating distorted surface measurements into meaningful downhole oscillation information without direct downhole sensors.
Solution Approach 2:
The patent replaces direct mechanical measurement of downhole RPM with a computational approach. Instead of using mechanical downhole sensors that would be complex and expensive, the system substitutes a mathematical model that processes surface mechanical measurements (torque and rotational speed) to infer downhole conditions, achieving accurate oscillation estimation without physical downhole instrumentation.
2Productivity
If downhole RPM oscillations are not accurately monitored, then drilling operations continue without interruption, but equipment damage and inefficiencies occur
Solution Approach 1:
The patent implements a feedback mechanism where the estimated downhole RPM oscillations are continuously monitored and fed back to the drilling control system. When oscillations exceed predetermined thresholds indicating harmful stick-slip conditions, the system generates alerts and can automatically adjust drilling parameters (rotational speed, weight on bit) to mitigate the oscillations, creating a closed-loop control system that prevents equipment damage while maintaining productivity.
3Measurement precision
If complex downhole sensing equipment is deployed to measure RPM oscillations directly, then measurement accuracy improves, but device complexity and cost increase
Solution Approach 1:
The patent uses the drillstring itself as an intermediary medium. Instead of deploying complex downhole sensors, the system utilizes the existing drillstring mechanical properties (inertia, damping, torsional stiffness) as a natural sensor network. The drillstring transmits torsional waves from downhole stick-slip events to the surface, where a mathematical model processes these waves to extract RPM oscillation information, effectively using the drillstring as a distributed sensing system.
Solution Approach 2:
The patent creates a computational copy of the downhole RPM signal from surface measurements. The mathematical model reconstructs the downhole oscillation waveform by processing surface torque and rotational speed data through equations that simulate drillstring dynamics, producing an accurate replica of what downhole sensors would measure without requiring physical downhole instrumentation.
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 provides accurate estimation of downhole RPM oscillations and STOPI, allowing for improved drilling efficiency, reduced equipment damage, and effective mitigation of stick-slip, enhancing drilling performance and operational control.
Implementation Method 1
obtaining inertia (JTD) of the top drive; and estimating torque TST of the drillstring based on the obtained TTD data, the obtained co data, and the obtained JTD data
Implementation Method 2
Stick-slip generates torsional waves travelling from downhole to the surface. The torsional waves are reflected in the top drive torque readings as oscillations in different degrees of magnitudes
Data Source
AI summary
Methods and apparatus for including obtaining raw surface data for present values of torque (TTD) generated by a top drive operably coupled with a drillstring, obtaining raw surface data for present values of rotational speed (ω) of the top drive corresponding to the TTD, obtaining inertia (JTD) of the top drive, and estimating torque TST of the drillstring based on the obtained TTD data, the obtained data, and the obtained JTD data. The estimated drillstring torque TST may be utilized to determine a surface torque oscillation performance index (STOPI).