Casing-Mounted EM Transducers with Soft Magnetic Layer
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Solution Overview
Problem
Existing systems for remote formation resistivity monitoring in oilfields face challenges due to variable and degrading contact resistance in galvanic electrodes and interference from carbon steel casing, which affects data quality and repeatability, and fail to adequately account for casing effects, rendering them unsuitable for routine oilfield applications.
Innovation Solution
The implementation of permanent electromagnetic (EM) monitoring devices with casing-mounted EM transducers featuring high permeability layers to amplify magnetic field signals and reduce interference from casing effects, using coils or piezoelectric/magnetostrictive elements with nonconductive, high-permeability sleeves to encircle the casing strings, enabling accurate monitoring of fluid saturations and resistivity distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If galvanic electrodes are used for resistivity monitoring, then measurement capability is provided, but contact resistance degrades over time reducing reliability
Solution Approach 1:
The patent replaces galvanic electrodes with electromagnetic transducers that use magnetic fields instead of electrical contact. The EM transducers generate and detect magnetic fields that penetrate the casing and interact with formation fluids, eliminating the need for direct electrical contact with the formation and thus avoiding contact resistance degradation.
Solution Approach 2:
The patent introduces an intermediary approach by using the steel casing itself as part of the EM measurement system. Instead of trying to achieve direct formation contact, the system uses the casing as a conduit for EM fields, with transducers mounted on the casing exterior that couple to the formation through the casing wall and cement sheath.
2Strength
If carbon steel casing is used for well construction, then structural integrity is maintained, but magnetic field interference reduces measurement accuracy
Solution Approach 1:
The patent converts the harmful magnetic interference from the steel casing into a beneficial effect by using the casing as part of the EM measurement system. The high permeability steel casing is used to couple magnetic fields from the transducers to the formation, and the system measures the total magnetic field including casing effects, using these effects as part of the measurement rather than trying to eliminate them.
Solution Approach 2:
The patent changes the measurement approach by moving from electrical resistivity measurements to magnetic field measurements. The EM transducers measure magnetic field strength and phase, which are less affected by the conductive steel casing compared to electrical measurements. The system uses the magnetic permeability of the steel casing to its advantage in coupling fields to the formation.
3Measurement precision
If insulated casing is used to avoid casing interference, then measurement accuracy improves, but practical applicability decreases
Solution Approach 1:
The patent replaces electrical resistivity measurements with electromagnetic field measurements that are less sensitive to casing materials. By using magnetic fields instead of electrical currents, the system can operate effectively with conventional steel casing without requiring insulated casing, thus maintaining both measurement accuracy and practical applicability.
4Measurement precision
If crosswell EM tomography is deployed with wireline transducers, then monitoring capability is provided, but permanent installation and structural stability are compromised
Solution Approach 1:
The patent merges the EM transducers with the permanent well infrastructure by mounting the transducers on the steel casing at the wellhead or in the surface well completion. This integration ensures permanent installation and structural stability, as the transducers become part of the permanent well equipment rather than temporary wireline tools.
Solution Approach 2:
The patent moves the EM measurement system from the wellbore interior (wireline deployment) to the wellhead or surface completion dimension. By mounting transducers on the external casing at the wellhead, the system achieves permanent installation while maintaining the ability to measure formation properties through the casing wall.
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 solution provides stable and accurate long-term monitoring of reservoir fluid saturations and resistivity, reducing signal degradation from casing effects and enhancing data quality, allowing for optimized production and injection strategies, and enabling effective tomographic mapping of fluid distributions.
Implementation Method 1
a layer of material that is nonconductive (a bulk conductivity of no more than 1 S/m and preferably less than 10−2 S/m) and having a high relative magnetic permeability (at least 200 and preferably greater than 500)
Implementation Method 2
Each borehole is provided with a casing string having one or more EM transducer modules
Implementation Method 3
a layer of material that is nonconductive (a bulk conductivity of no more than 1 S/m and preferably less than 10−2 S/m)
Data Source
AI summary
Illustrative permanent electromagnetic (EM) monitoring systems and methods have a casing string positioned inside a borehole and equipped with one or more EM transducer modules having a layer of soft magnetic material that substantially encircles the casing string to amplify a signal response of a magnetic field transmitting and/or sensing element. The layer preferably has an axial dimension at least twice an axial dimension of the magnetic field sensing element, with a relative permeability at least twice that of the casing material. The magnetic field transmitting element can be a coil. The magnetic field sensing element can be a coil or a piezoelectric or magnetostrictive element that applies stress to an optical fiber. A well interface system communicates with the one or more EM transducer modules to transmit and/or collect EM signals over time. Additional casing strings may be provided in other nearby boreholes to enable tomographic mapping and monitoring of fluid interfaces in the reservoir.