Cross-well EM Imaging Resolution via Pulsed Sources
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Solution Overview
Problem
Conventional cross-well and borehole-to-surface electromagnetic (EM) surveying techniques are limited by low frequency operation due to signal attenuation by brine in hydrocarbon reservoirs, resulting in poor imaging resolution and inability to determine optimal frequencies for investigation.
Innovation Solution
The use of high-power pulsed EM sources, modern low-noise magnetic field sensors, spatial oversampling, and super-resolution image enhancement, along with injected magnetic nanofluids to improve image resolution and contrast, allowing for higher frequency operation and better imaging of hydrocarbon reservoirs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If continuous-wave EM sources are used at low frequency to penetrate brine-filled reservoirs, then signal detection is possible, but imaging resolution is severely limited
Solution Approach 1:
The patent uses pulsed EM sources instead of continuous-wave sources. The pulsed operation allows the system to transmit high-power signals at higher frequencies during brief intervals, achieving both penetration through brine and improved imaging resolution through higher frequency components in the pulse spectrum.
Solution Approach 2:
The patent changes the temporal characteristics of the EM source from continuous to pulsed, and operates at higher frequencies than conventional continuous-wave systems. This parameter change enables the system to overcome the frequency-dependent attenuation limitation while maintaining signal detectability through the use of high-power pulses and advanced signal processing.
2Measurement precision
If higher frequency EM sources are used to improve imaging resolution, then wavelength decreases and resolution improves, but signal attenuation by brine increases
Solution Approach 1:
By using pulsed EM sources with high peak power, the system can operate at higher frequencies where the pulse spectrum contains significant energy, while the duty cycle is kept low to minimize average power loss to attenuation. The pulsed nature allows the use of higher frequencies that would be too attenuated in continuous operation.
Solution Approach 2:
The patent performs preliminary actions by injecting magnetic nanofluids into the reservoir before EM surveying. This modifies the reservoir's magnetic properties in advance, enhancing the contrast and detectability of fluid flow paths, which compensates for the energy loss due to higher frequency attenuation.
3Reliability
If conventional receivers are used, then thermal noise limits detection, but modern low-noise magnetic field sensors enable detection of higher frequency signals
Solution Approach 1:
The patent replaces conventional EM receivers with modern low-noise magnetic field sensors. This substitution enables the system to detect the much weaker higher frequency signals that result from using pulsed EM sources, overcoming the thermal noise limitations of conventional receivers.
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 enhances EM imaging resolution by up to 5 to 10 times the inter-well spacing, enabling more accurate mapping of fluid distribution and dynamic flow paths in hydrocarbon reservoirs.
Implementation Method 1
A pulsed EM source generates pulses of electromagnetic energy which are recorded by one or more other EM energy receivers
Implementation Method 2
injected magnetic nanofluids to improve image resolution and contrast, allowing for higher frequency operation and better imaging of hydrocarbon reservoirs
Data Source
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Figure 3A
AI summary
Cross-well electromagnetic (EM) imaging is performed using high-power pulsed magnetic field sources, time-domain signal acquisition, low-noise magnetic field sensors, spatial oversampling and super-resolution image enhancement and injected magnetic nanofluids. Inter-well images are generated mapping electromagnetic (EM) signal speed (group velocity) rather than conductivity maps. EM velocity maps with improved resolution for both native and injected fluids are provided.