Subsurface Electrical Conductivity Reconstruction via Wavefield Correlation
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Solution Overview
Problem
Current methods for analyzing subsurface electromagnetic survey data, such as CSEM inversion, face challenges with timing, stability, and computation limitations, particularly in processing and interpreting complex and large-scale data sets in real-time, and lack effective solutions for cross-well, borehole-to-surface, and surface-to-borehole configurations.
Innovation Solution
The method involves receiving electromagnetic survey data from a first downhole transceiver and a second transceiver, correlating incident and scattered wave components to generate images of subsurface features, using either analytic continuation or fullwave simulation, primarily focusing on narrow frequency ranges and applying these techniques to cross-well, borehole-to-surface, and surface-to-borehole configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If CSEM inversion is used to reconstruct subsurface conductivity distributions, then accurate subsurface models are obtained, but timing, stability, and computation limitations occur
Solution Approach 1:
The patent applies downward continuation imaging as an alternative to traditional CSEM inversion. Instead of using iterative inversion algorithms that suffer from stability issues, the method uses a direct imaging approach based on wavefield correlation, reversing the conventional problem-solving methodology to achieve both accuracy and stability.
Solution Approach 2:
The patent replaces the iterative mathematical inversion process with a physics-based wavefield correlation method. By substituting the computational inversion mechanism with a direct wavefield imaging approach, the method eliminates the stability and convergence issues inherent in traditional inversion while maintaining subsurface reconstruction accuracy.
2Measurement precision
If CSEM inversion is used to reconstruct subsurface conductivity distributions, then accurate subsurface models are obtained, but computation time increases
Solution Approach 1:
The patent performs preliminary wavefield propagation and correlation operations before final image reconstruction. By pre-computing the downward continued wavefields and storing them for subsequent correlation with recorded data, the method reduces the computational burden during the actual imaging process, enabling faster processing while maintaining accuracy.
Solution Approach 2:
The patent replaces the computationally intensive iterative inversion process with a direct wavefield correlation method. This substitution eliminates the need for multiple iterative cycles, significantly reducing computation time while producing accurate subsurface images through direct wavefield imaging.
3Measurement precision
If traditional inversion methods are used, then subsurface electrical properties can be reconstructed, but instability and ad hoc parameter adjustments are required
Solution Approach 1:
The patent makes the imaging process self-adjusting by using the recorded electromagnetic data itself to drive the wavefield correlation. The method automatically adapts to the specific survey conditions and subsurface properties without requiring manual parameter tuning, as the wavefield correlation naturally optimizes the imaging results based on the actual measured data.
Solution Approach 2:
The patent implements a feedback mechanism where the downward continued wavefields are correlated with the actually recorded data, and the resulting image provides feedback on subsurface structure. This automatic feedback loop eliminates the need for manual parameter adjustments, as the system self-calibrates based on the measured electromagnetic responses.
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 provides faster and more stable imaging solutions compared to traditional inversion methods, capable of reconstructing subsurface resistivity variations and electrical properties, offering alternative and efficient subsurface electrical conductivity reconstruction without the instability and ad hoc parameter adjustments inherent in inverse solutions.
Implementation Method 1
The image is based at least in part on one or more interference patterns of the incident and scattered wave components
Implementation Method 2
controlled-source electromagnetic (CSEM) data include a series of electric or magnetic dipole sources that are energized in a borehole, on the surface of the earth, or near the seafloor, and measurements of magnetic and/or electric fields are made
Data Source
AI summary
Methods and related systems are described for analyzing electromagnetic survey data. Electromagnetic survey data of a subterranean formation is obtained using at least a downhole transceiver deployed in a borehole and a transceiver positioned on the surface or in another borehole. The electromagnetic survey data includes an incident wave component and a scattered wave component. The incident and scattered components are correlated so as to generate an image of the subterranean formation indicating spatial locations of one or more features, for example, electrical properties such as resistivity variations, in the formation. The image is based at least in part on one or more interference patterns of the incident and scattered wave components. The correlation preferably includes generating a simulation of the incident wave component propagated into the formation, and convolving the simulated propagated incident wave component with the scattered wave component. The simulation can be performed using an analytic continuation or a fullwave simulation.