Surface Torque Oscillation Performance Index for Drilling
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Solution Overview
Problem
Existing methods for measuring surface torque oscillations in drilling operations, such as the Surface Stick Slip Index (SSSI), face challenges with variable reference torque and fixed time periods, which can lead to inefficient representation of stick-slip oscillations due to varying formations and hole depths.
Innovation Solution
The Surface Torque Oscillation Performance Index (STOPI) is introduced, calculated as the difference between maximum and minimum surface torque values divided by a configurable constant torque value, with a dynamically specified time window corresponding to the fundamental frequency of the drillstring, providing a fractional value that indicates the magnitude and severity of surface torque fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a fixed time period is used to determine maximum and minimum torque values, then the calculation method is simple, but it may not efficiently represent stick-slip oscillations when oscillation time period varies with hole depth
Solution Approach 1:
The patent applies dynamics by making the time window dynamic rather than fixed. The time window is adjusted based on the fundamental frequency of the drillstring, which varies with hole depth. This allows the measurement system to adapt to changing oscillation characteristics as drilling progresses, improving measurement precision without significantly complicating the calculation process.
2Adaptability or versatility
If a variable reference torque is used in the denominator, then the index adapts to different formations, but it complicates the interpretation of oscillation magnitude
Solution Approach 1:
The patent applies parameter changes by using a constant reference torque value instead of a variable one. This simplifies the STOPI index interpretation because the denominator remains fixed, making it easier to compare oscillation magnitudes across different formations and drilling conditions. The adaptability is achieved through the dynamic time window and the STOPI calculation method itself, rather than through variable reference torque.
3Reliability
If a large fixed time period is used to cover oscillation cycles, then all oscillation cycles are captured, but the response time of the index is delayed
Solution Approach 1:
The patent resolves this contradiction by making the time window dynamic. Instead of using a large fixed time period, the system calculates the fundamental frequency of the drillstring and sets the time window based on this frequency. This allows the time window to be just large enough to capture the necessary oscillation cycles for accurate measurement, without introducing unnecessary delay. The time window adapts to the actual oscillation characteristics, ensuring both reliable cycle coverage and timely index response.
Data Source
AI summary
A system and method for drilling a wellbore with a drill rig by: rotating a drillstring and a drill bit with a drill rig drive system; applying a weight of the drillstring on the drill rig; measuring surface torque oscillations of the drill string via: determining a fundamental oscillation time period; select a time window based on the fundamental oscillation time period; collecting torque present value data of the drill string for the selected time window; determining an amplitude of torque oscillation from the collected torque present value data; determining a reference torque; and dividing the determined amplitude of torque oscillation by the determined reference torque to obtain a surface torque oscillation performance index, whereby the measurement of the surface torque oscillations of the drill string is a fractional value to indicate the magnitude and severity of surface torque fluctuations of the drilling string; and modifying a drilling parameter based on the surface torque oscillation performance index.