Shear Failure Leakoff Test for Formation Stress Characterization
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Solution Overview
Problem
The existing methods for characterizing formation stresses, particularly using leakoff pressure, are inconsistent with stress states in reverse-fault settings or areas under compression, as leakoff pressure is often below the overburden pressure, failing to provide a reasonable estimate of minimum principle stress.
Innovation Solution
An apparatus and method that induce shear failure during a leakoff test to determine stress magnitudes, using the Mohr-Coulomb failure criterion and constructing solution spaces with orthogonal stresses, where the leakoff pressure is used to establish a new line of shear failure, allowing for characterization of stress states in formations under shear failure conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If leakoff pressure is used to determine minimum principle stress under the standard tensile failure assumption, then the method is simple and widely applicable, but the results are inconsistent with stress states in reverse-fault settings or areas under compression where leakoff pressure is below overburden pressure
Solution Approach 1:
The patent changes the fundamental assumption parameter from tensile failure mode to shear failure mode. This parameter change allows the leakoff pressure interpretation to be consistent with stress states in reverse-fault settings and areas under compression, where the formation fails in shear rather than tension. The Mohr-Coulomb failure criterion is applied to calculate minimum principle stress based on shear failure mechanics rather than tensile failure mechanics.
2Adaptability or versatility
If the standard assumption of tensile failure is applied to all formations, then the analysis method remains consistent and simple, but it fails to account for shear failure conditions in certain stress states
Solution Approach 1:
The patent introduces dynamic adaptability by providing multiple failure mode analysis paths. The system can dynamically select between tensile failure analysis and shear failure analysis based on the specific stress state conditions. This is achieved by evaluating whether the stress state indicates normal-fault, reverse-fault, or strike-slip conditions, and applying the appropriate failure mode assumption accordingly.
3Measurement precision
If shear failure is induced during leakoff test to determine stress magnitudes, then accurate stress characterization is achieved for reverse-fault settings, but the test complexity and analysis requirements increase
Solution Approach 1:
The patent uses the Mohr-Coulomb failure criterion as an intermediary framework that bridges the gap between leakoff pressure measurements and stress state characterization. This criterion serves as a mediator that translates pressure data into meaningful stress information by providing a mathematical relationship between shear stress, normal stress, and material properties (cohesion and friction angle). The criterion envelope acts as an intermediary tool to interpret whether shear failure has occurred and to calculate corresponding stress magnitudes.
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 provides a more accurate characterization of stress states in formations, enabling better planning and execution of hydrocarbon exploration, development, and production activities by determining the range of possible stress states consistent with shear failure, including normal-fault, reverse-fault, and strike-slip fault settings.
Implementation Method 1
the drilling fluid penetrates the fracture system, moves through permeable paths, and interacts with the stress field of the formation
Implementation Method 2
As pore pressure increases in the fracture system, the formation is induced to fail along the fracture in a shear mode
Implementation Method 3
A line of shear failure that defines the failure envelope can generally be determined with values for cohesion and a coefficient of friction
Data Source
AI summary
An apparatus (20) and method for characterizing stresses in a formation (10) based on leakoff pressure measured in the formation (10). The method includes determining a line of shear failure (52) as a function of leakoff pressure (LOP) measured in the formation (10), determining a vertical stress (Sv), and determining each of a lower limit (Sh,limit) and an upper limit (SH,limit) as a function of the vertical stress (Sv) and the leakoff pressure (LOP).