Imminent Rock Failure Estimation Using Multi-Stage Triaxial Compression
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Solution Overview
Problem
Current methods for estimating imminent rock failure in core samples during mechanical testing are inaccurate and inefficient, particularly for unconventional shale formations, due to the difficulty in obtaining and testing sufficient high-quality core plugs, leading to unreliable determination of Mohr-Coulomb failure envelopes.
Innovation Solution
A method and apparatus for estimating imminent rock failure by continuously monitoring stress parameters such as radial strain and acoustic emission counts over time, using a series of reference lines to identify deviations and determine the precise point of failure, allowing for accurate calibration of the Mohr-Coulomb failure envelope even with a single core plug.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional methods are used to obtain and test multiple high-quality core plugs, then sufficient data for Mohr-Coulomb failure envelope determination can be obtained, but the process becomes time-consuming and sample availability becomes limiting
Solution Approach 1:
The patent applies preliminary action by performing multiple stages of compression testing on a single core plug before failure occurs. The test progresses through incremental loading stages (e.g., 50%, 75%, 100% of estimated failure load) to accumulate sufficient data points for Mohr-Coulomb envelope determination, eliminating the need to obtain multiple core plugs in advance
Solution Approach 2:
The patent changes testing parameters by applying varying confining pressures and axial loads in multiple stages throughout the test. This allows data collection across a range of stress states from a single core plug, enabling accurate Mohr-Coulomb envelope determination without requiring multiple separate samples
2Measurement precision
If multiple core plugs are tested to ensure sufficient data quality, then accurate mechanical parameters can be obtained, but sample availability and testing efficiency become constrained
Solution Approach 1:
The patent merges multiple testing stages into a single continuous test on one core plug. By combining incremental loading stages, acoustic emission monitoring, and strain measurements throughout the test duration, sufficient data is accumulated to determine mechanical parameters with the same precision as traditional multi-sample methods
Solution Approach 2:
The patent maintains continuous monitoring and data collection throughout the entire multi-stage test duration. Acoustic emission sensors and strain gauges continuously record data as the core plug progresses through each loading stage, ensuring no useful information is lost and maximizing data quality from a single sample
3Ease of operation
If conventional compression testing is used without continuous monitoring, then simpler testing procedures can be applied, but accurate detection of imminent failure becomes difficult
Solution Approach 1:
The patent implements feedback by continuously monitoring acoustic emission signals and strain measurements during each loading stage. This real-time feedback allows the testing system to detect imminent failure conditions and adjust subsequent loading accordingly, improving failure detection accuracy while maintaining procedural simplicity through automated monitoring
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 enables precise and accurate estimation of imminent rock failure, improving the calibration of Mohr-Coulomb failure envelopes and reducing the uncertainty in mechanical behavior of core samples, especially in limited sample scenarios, thereby optimizing hydraulic fracturing operations and wellbore stability.
Implementation Method 1
using a change in measurements of at least one stress parameter of the core sample over time responsive to an applied stress to estimate imminent rock failure in the core sample. This may include estimating the imminent rock failure using differences between portions of a curve generated based on the measurements. The curve may be generated based on the measurements, and may include at least one of: i) radial strain with time; and ii) acoustic emission counts with time.
Data Source
AI summary
Methods and apparatus for evaluation of an earth formation including evaluating a core sample obtained from the formation. Methods include using a change in measurements of at least one stress parameter of the core sample, such as radial strain, axial stress, and acoustic emission counts, over time responsive to an applied stress to estimate imminent rock failure in the core sample. This may include estimating the imminent rock failure using differences between portions of a curve generated based on the measurements. A method employing calculating a rate of change between a plurality of measurements of at least one stress parameter of the core sample over time responsive to an applied stress; and determining a point of imminent failure using the rate of change in the plurality of measurements of the at least one stress parameter is also included.