Multi-scale fatigue analysis for bottom hole assemblies
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Solution Overview
Problem
Current fatigue analysis methods for bottom hole assemblies (BHAs) in drilling operations are inadequate due to uncertainties in predicting fatigue life, particularly for complex load sequences and notch plasticity, leading to potential failures in drill pipes and drill collars.
Innovation Solution
A multi-scale approach for fatigue analysis using three length scales (BHA, component, and feature scales) that employs beam-type finite element models, continuum element-based models, and fatigue criteria like stress life, strain life, and crack propagation approaches, along with mean stress correction, to accurately determine fatigue life and damage of critical features like port holes and threaded connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional fatigue analysis methods are used, then analysis simplicity is maintained, but prediction accuracy deteriorates due to uncertainties in complex load sequences and notch plasticity
Solution Approach 1:
The patent divides the fatigue analysis into three distinct length scales: BHA scale (overall assembly), component scale (individual parts like drill collars), and feature scale (specific fatigue-critical features like port holes and threaded connections). This segmentation allows each scale to be analyzed with appropriate methods and models, improving overall prediction accuracy while managing complexity through hierarchical organization
Solution Approach 2:
The patent implements a nested multi-scale modeling approach where feature-scale models are embedded within component-scale models, which are in turn embedded within BHA-scale models. This nesting allows detailed local analysis at the feature level to be integrated into broader component and assembly-level analyses, enabling accurate fatigue life prediction without requiring equally detailed analysis throughout the entire system
2Strength
If stress life approach is used, then infinite life or high-cycle finite life applications are suitable, but notch plasticity effects cannot be captured
Solution Approach 1:
The patent transitions from stress-based parameters to strain-based parameters for fatigue analysis. The strain life approach uses cyclic strain amplitude and mean strain as controlling parameters, which directly capture notch plasticity effects that stress-based methods miss. This parameter change enables accurate prediction of fatigue life in finite life applications where plastic deformation occurs at stress concentrations
3Measurement precision
If crack growth life approach is used, then fracture mechanics analysis is applied, but accurate initial crack size determination is difficult
Solution Approach 1:
The patent performs preliminary fatigue analysis using the strain life approach to estimate the number of cycles to crack initiation before applying fracture mechanics for crack growth analysis. This preliminary action provides an estimated initial crack size based on strain-life predictions, which then serves as the starting point for crack growth calculations, eliminating the need to arbitrarily determine initial crack sizes
4Reliability
If conservative parameters are used, then consistent comparative analysis of different BHA components is enabled, but fatigue life prediction uncertainty remains high
Solution Approach 1:
The patent applies local quality by using fatigue-critical features (such as port holes, threaded connections, and radius changes) as specific locations for detailed strain life analysis. Instead of applying conservative parameters uniformly across all components, the method identifies and analyzes only the critical features where fatigue initiation is most likely, providing locally accurate predictions that maintain consistency for comparative analysis while reducing overall uncertainty
Data Source
AI summary
A system and a method analyze fatigue damage of a bottom hole assembly (“BHA”), and more specifically, use a multi-scale approach for fatigue analysis of a BHA. Three length scales may be used in modeling of a BHA, namely the BHA scale, the component scale and the feature scale. Loading conditions for each collar/tool of the BHA may be determined, such as by use of a beam model, and may be applied to the finite element models for the collar/tool to determine the fatigue damage of each fatigue susceptible feature of each collar/tool. A cumulative fatigue damage of each critical feature may be determined, and the weakest component of the BHA may be identified. Prognostic and diagnostic implementation with well survey and drilling data may monitor fatigue damage of critical components of the BHA.