Modified Plane-of-Weakness Model for Anisotropic Borehole Stability
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Solution Overview
Problem
Existing methods for predicting and mitigating wellbore instability in anisotropic formations, such as those with laminated or fractured rocks, are limited in accurately determining the onset of sliding along weak planes and subsequent borehole failure, leading to increased drilling costs and operational challenges.
Innovation Solution
A computer-implemented method and system that utilize a Modified Plane-of-Weakness (MPoW) model to analyze near-borehole stress distribution, characterize anisotropy, and determine optimal mud weights to prevent instability, incorporating data from various sources like logging tools and seismic data to model borehole stability and predict potential failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional wellbore stability models are used in anisotropic formations, then the models are simpler to implement, but they fail to accurately predict sliding along weak planes and subsequent borehole failure
Solution Approach 1:
The patent transforms the complex anisotropic elasticity problem into a manageable form by changing parameters: it introduces effective stress parameters and orientation-dependent strength parameters that capture anisotropic effects without requiring full tensor calculations. The model uses transformed stress components (σr, σθ, σz, τrθ, τrz, τθz) and orientation angles to describe the mechanical behavior, making the complex anisotropic problem tractable while maintaining prediction accuracy for sliding along weak planes
Solution Approach 2:
The patent applies composite material theory by treating the anisotropic formation as a composite structure with distinct weak planes embedded in the matrix material. It combines the mechanical properties of the intact rock with the strength characteristics of the weak planes, using a unified model that accounts for both the host formation and the discontinuities. This composite approach allows accurate prediction of sliding failure along weak planes while maintaining model efficiency
2Stability of the object's composition
If mud weight is increased to prevent borehole collapse, then wellbore stability improves, but the risk of inducing fractures and lost circulation increases
Solution Approach 1:
The patent applies local quality by determining direction-dependent strength parameters for the formation. It calculates the induced stress state at different orientations around the borehole and identifies the specific directions where tensile stresses are most likely to cause fracturing. This allows the model to predict fracture risk in specific local zones rather than assuming uniform conditions, enabling more precise mud weight optimization that prevents both collapse and fracturing
Solution Approach 2:
The patent performs preliminary action by calculating the complete stress state and identifying critical mud weight thresholds before drilling operations begin. It determines the minimum mud weight required to prevent collapse and the maximum mud weight that avoids inducing fractures, establishing a safe operating window in advance. This preliminary analysis allows engineers to plan drilling operations with optimized mud weight programs, preventing both wellbore instability and fracture-related problems before they occur
Data Source
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AI summary
A method can include receiving data that characterizes anisotropy of a formation; receiving a model that models one or more planes of weakness in an anisotropic formation; and, based at least in part on the model and the data, outputting information germane to stability of a bore in an anisotropic formation.