Fiber Optic Wellbore Strain Sensing for Continuous Stress Logging
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Solution Overview
Problem
Existing subsurface stress measurement techniques, such as hydraulic fracturing, provide only discrete and singular stress measurements at specific locations along a wellbore, lacking a continuous log of stress estimation, and may cause unintended fracturing or require costly core sampling.
Innovation Solution
A system utilizing a distributed strain sensing system, like a fiber optic cable, to measure strain along a wellbore, combined with a controller to determine elastic properties and stress states continuously, applying controlled perturbations to the casing without causing fracturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If hydraulic fracturing method is used to determine subsurface stress, then minimum principal stress magnitude can be determined, but only discrete and singular stress measurements are obtained at specific locations, lacking continuous stress estimation
Solution Approach 1:
The patent replaces traditional mechanical stress measurement methods (hydraulic fracturing) with an optical sensing system. A distributed strain sensing system using optical fibers measures strain along the wellbore, which is then converted to stress information. This substitution enables continuous stress estimation along the entire wellbore length rather than discrete point measurements, resolving the contradiction between measurement precision and information completeness.
Solution Approach 2:
The patent introduces strain as an intermediary parameter to bridge the gap between direct stress measurement and continuous monitoring. By measuring strain in the casing or wellbore structure and using mechanical property relationships to convert strain to stress, the system achieves continuous stress estimation without requiring direct continuous stress sensors. This intermediary approach enables the transition from discrete stress measurements to continuous stress logs.
2Measurement precision
If hydraulic fracturing is performed to obtain stress measurements, then stress data can be obtained, but unintended fracturing may occur or costly core sampling is required
Solution Approach 1:
The patent replaces mechanical stress induction methods (hydraulic fracturing) with non-invasive optical strain sensing. Instead of applying mechanical loads that cause fracturing, the system uses optical fibers to measure strain in the existing wellbore structure under in-situ conditions. This substitution eliminates the harmful effect of unintended fracturing while maintaining stress measurement capability through the strain-stress relationship.
Solution Approach 2:
The patent utilizes the wellbore structure itself (casing or concrete) as the sensing element. The existing structural components serve dual purposes: maintaining wellbore integrity and providing the medium for strain measurement. By making the wellbore structure self-servicing as both a structural and sensing element, the system avoids additional invasive procedures like core sampling or fracturing that would compromise the structure.
3Ease of manufacture
If discrete stress measurements are taken at specific locations, then stress data can be obtained, but comprehensive understanding of subsurface formations along the wellbore length is limited
Solution Approach 1:
The patent implements a universal measurement system where a single distributed optical sensing infrastructure serves multiple functions: measuring strain, determining stress, characterizing formation mechanical properties, and providing continuous spatial coverage. This multi-functional system replaces multiple discrete measurement operations, achieving comprehensive formation understanding while maintaining ease of implementation through a unified approach.
Solution Approach 2:
The patent establishes continuous strain measurement capability along the entire wellbore length using distributed optical sensing. This continuous measurement action provides uninterrupted stress and formation characterization data, eliminating the gaps inherent in discrete measurements. The continuous data stream enables comprehensive understanding of subsurface formations while maintaining practical implementability through established optical sensing technologies.
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
Enables continuous stress prediction and mechanical property characterization along the wellbore length, reducing uncertainty and cost by avoiding fracturing and providing a comprehensive understanding of subsurface formations.
Implementation Method 1
measuring a value related to a strain resultant from the stress applied to the casing of the length of the wellbore
Implementation Method 2
determining a value related to an elastic property of a formation extending along the length of the wellbore based on the value related to the stress applied to the casing and the value related to the strain resultant from the stress applied to the casing
Data Source
AI summary
A system for monitoring and establishing mechanical properties of a formation may include a strain sensing system and a controller. The strain sensing system may include an elongated fiber, a light emitter, and a detector. The elongated fiber may be or may include a fiber optic cable. Monitoring and establishing mechanical properties of a wellbore may include determining a stress applied to a casing of a length of the wellbore and sensing, with the strain sensing system, a strain that may be resultant from the stress applied to the casing. Based on the stress applied to the casing and the sensed strain, the controller may determine a value related to a mechanical property of the formation extending along the wellbore.