Horizontal Stress Estimation via Elastic-Plastic Integration
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Solution Overview
Problem
Current methods for estimating horizontal stresses in reservoirs are inadequate as they rely on unrealistic assumptions about the earth's elasticity and homogeneity, failing to accurately account for frictional strength and non-elastic rock properties, especially in unconventional reservoirs and areas with faults and fractures.
Innovation Solution
A new method that integrates uniaxial elasticity and frictional equilibrium concepts to provide continuous stress solutions along a wellbore, using percentile filtering to combine results from frictional equilibrium and elastic stress solutions, considering both discontinuities and pre-failure stress accumulation, and incorporating uniaxial compressive strength for a more realistic estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If plain-strain elastic solutions are used to estimate horizontal stresses, then the earth is assumed to be an elastic, homogenous and isotropic medium which simplifies calculations, but this assumption is not valid in the presence of faults, folds and plastic rocks leading to erroneous stress estimation
Solution Approach 1:
The patent changes the fundamental parameters of the earth model from elastic to non-elastic, transitioning from Hooke's law to plasticity theory with yield criteria (von Mises, Drucker-Prager). This allows the model to accommodate plastic rocks and fault zones while maintaining analytical tractability through modified stress-strain relationships.
Solution Approach 2:
The patent applies different material models to different regions: elastic behavior in intact rock zones and plastic behavior in zones with faults, folds, or plastic rocks. This localized approach allows the model to capture spatial variations in rock rheology without requiring a fully numerical solution throughout the entire domain.
2Measurement precision
If frictional equilibrium based calculations are used, then stress estimation can be performed considering frictional strength of faults, but this technique requires more input parameters and fails to provide continuous stress estimation along the wellbore
Solution Approach 1:
The patent merges frictional equilibrium calculations with plasticity theory, combining the strengths of both approaches. The frictional strength of faults is incorporated as a boundary condition within the plasticity framework, allowing continuous stress estimation along the wellbore while accounting for fault mechanics. This unified model reduces the number of independent input parameters required compared to pure frictional equilibrium methods.
3Measurement precision
If analytical solutions for non-elastic medium are developed, then realistic rock properties can be considered, but the complexity and multi-dimensional nature of the problem makes such solutions difficult to obtain
Solution Approach 1:
The patent segments the earth model into distinct zones based on rock rheology: elastic zones, plastic zones, and fault zones. Each zone is governed by appropriate constitutive equations, allowing analytical solutions to be constructed piecewise throughout the domain. This segmentation reduces the overall complexity by treating different regions separately rather than requiring a fully coupled three-dimensional non-elastic solution.
Solution Approach 2:
The patent introduces plasticity theory as an intermediary framework that bridges elastic theory and fully numerical non-elastic solutions. By using yield criteria and flow rules as intermediate mathematical structures, the patent enables analytical treatment of plastic rock behavior without requiring complex numerical algorithms, thus reducing solution complexity while maintaining realism.
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
This approach allows for more accurate and continuous estimation of horizontal stresses, enhancing the planning and execution of drilling and hydraulic stimulation operations in unconventional reservoirs by providing a more realistic consideration of rock rheology and reducing the risk of wellbore failures.
Implementation Method 1
integrates uniaxial elasticity and frictional equilibrium concepts to provide continuous stress solutions
Implementation Method 2
frictional strength and realistic elasticity into consideration
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
This disclosure describes a method for calculating the horizontal stresses that integrate both frictional equilibrium and uniaxial elasticity assumptions. The results are more accurate than either of the assumptions.