Downhole Flat-Jack Stress Measurement for Deep Borehole Walls
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Solution Overview
Problem
Current methods for measuring in-situ stress in deep rock formations are unreliable due to invalid assumptions and operational limitations, leading to significant uncertainties in geomechanical modeling and costly failures in drilling and subsurface operations.
Innovation Solution
A tool and method using a flat-jack stress measurement device that cuts a slot in the borehole wall and measures stress by inflating a flat-jack to compensate for stress release, allowing direct measurement of in-situ stress through hydraulic fluid pressure, controlled by a wireline system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If hydraulic fracturing is used to measure in-situ stress, then the measurement process is simple and consistent for S hmin, but the estimate of S Hmax is unreliable and the method has operational limitations in ultra-deep formations
Solution Approach 1:
The invention extracts the stress measurement function from the complex hydraulic fracturing process by using a dedicated flat-jack device that directly applies controlled deformation to the borehole wall. This separates the measurement of principal stress components from the confounding factors of fluid injection, allowing reliable measurement of both S hmin and S Hmax without operational limitations.
Solution Approach 2:
The flat-jack stress measurement device provides universal functionality by measuring all three principal stress components (S v, S hmin, S Hmax) through a single integrated system, whereas hydraulic fracturing can only reliably measure S hmin and requires separate, less reliable methods for the other components.
2Adaptability or versatility
If borehole breakouts are used to infer S Hmax, then the method can be applied in deep wells, but the reliability remains very poor due to invalid assumptions
Solution Approach 1:
The invention replaces the indirect geometric inference method (borehole breakout analysis) with a direct mechanical measurement system. The flat-jack device physically applies controlled deformation and directly measures the resulting stress state, eliminating reliance on invalid assumptions about rock elasticity, homogeneity, and isotropy that plague breakout analysis.
3Reliability
If direct measurement methods are developed for deep formations, then reliable stress data can be obtained, but the device complexity and operational difficulty increase
Solution Approach 1:
The flat-jack stress measurement device employs a nested structure where the flat-jack itself is contained within a housing that includes integration with the slot cutting system. This modular nested design allows the complex measurement functionality to be packaged in a compact, deployable form that can be lowered into the borehole and operated from surface.
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
Provides reliable and direct measurement of in-situ stress components, reducing uncertainties in geomechanical modeling and improving the success of drilling and subsurface operations.
Implementation Method 1
a flat-jack stress measurement device that cuts a slot in the borehole wall and measures stress by inflating a flat-jack to compensate for stress release, allowing direct measurement of in-situ stress through hydraulic fluid pressure
Data Source
Figure 1
Figure 2A~2E
Figure 4~6B
AI summary
A tool (100) for measuring direct in-situ stress in rock (10) surrounding a borehole (12) includes: a slot cutting system (136), a flat-jack stress measurement device (134), a hydraulic system (124), and a sensor (514). The slot cutting system (136) cuts a slot (502) having an original width in the rock (10) surrounding the borehole (12). The flat-jack stress measurement device (134) fits into the slot (502). The hydraulic system (124) expands the flat-jack stress measurement device (134) when it is in the slot to the original width of the slot (502). The sensor (514) measures pressure in the hydraulic system (124) when the flat-jack stress measurement device (134) has expanded to the original width of the slot (502).