Dynamic Torque and Drag Model Selection for Downhole Strings
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Solution Overview
Problem
The oil and gas industry faces challenges in accurately determining torque and drag of downhole strings due to the inconsistency between soft string and stiff string models, with field tests often required to determine which model yields better results, and existing methods fail to account for wellbore shape and stiffness effectively.
Innovation Solution
A system and method that analyze the downhole string by partitioning it into segments and determining whether to use the soft string model or the stiff string model based on the string's stiffness and the wellbore's dog-leg severity, using equations to calculate deflection and boundary spaces to decide the appropriate model for torque and drag calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the stiff string model is used to account for string stiffness, then the theoretical accuracy should improve, but the model complexity increases and may yield less accurate results in practice
Solution Approach 1:
The patent changes the parameter of model selection from a static choice to a dynamic decision based on calculated deflection values. By computing the deflection of the downhole string and comparing it to the wellbore clearance, the system automatically selects between soft string and stiff string models, adapting the complexity level to the actual physical conditions rather than always using the more complex stiff string model
Solution Approach 2:
The patent introduces dynamics into the model selection process by making it conditional on real-time calculations of string deflection and wellbore geometry. The system dynamically determines whether to apply soft or stiff string modeling based on the computed deflection values, allowing the approach to adapt to varying downhole conditions throughout the wellbore
2Measurement precision
If field tests are performed to determine which model yields better results, then the accuracy can be improved, but the time and cost increase
Solution Approach 1:
The patent performs preliminary calculations of string deflection and wellbore clearance before actual drilling operations begin. By pre-determining which model (soft or stiff string) is appropriate based on the calculated deflection values and comparing them to wellbore geometry, the system eliminates the need for time-consuming field tests to validate model accuracy
Solution Approach 2:
The system performs self-validation through automated calculations that compare computed deflection values against wellbore clearance parameters. This self-service approach allows the method to determine its own appropriate model selection without requiring external field testing, reducing both time and cost while maintaining accuracy
3Ease of manufacture
If the soft string model is used to simplify calculations, then the ease of computation improves, but the accuracy deteriorates when string stiffness is significant
Solution Approach 1:
The patent changes the parameter of model selection from a fixed choice to a variable decision based on calculated deflection. By computing the deflection of the downhole string and comparing it to the wellbore clearance, the system automatically selects between soft string (simpler) and stiff string (more accurate) models, adapting the calculation complexity to the actual physical conditions
Solution Approach 2:
The patent introduces dynamics into the calculation approach by making model selection conditional on real-time calculations of string deflection and wellbore geometry. The system dynamically determines whether to apply soft or stiff string modeling based on the computed deflection values, allowing the approach to adapt to varying downhole conditions throughout the wellbore
Data Source
AI summary
The embodiments include systems and methods to determine torque and drag of a string. A method includes analyzing a plurality of continuous segments of a string deployed in a wellbore, and determining a deflection of the plurality of continuous segments from a node of the string and a tortuosity deflection of the wellbore. In response to a determination that deflection of the plurality of continuous segments from the node of the string is greater than the tortuosity deflection of the wellbore, the method includes applying a soft string model to determine a torque and a drag of the string. In response to a determination that deflection of the plurality of continuous segments from the node of the string is not greater than the tortuosity deflection of the wellbore, the method includes applying a stiff string model to determine a torque and a drag of the string.