Magneto-seismic Exploration for Subsurface Conductivity Mapping
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Solution Overview
Problem
Conventional seismic surveys face challenges in distinguishing hydrocarbon deposits from brine due to poor spatial resolution and inaccurate resistivity maps, primarily caused by diffusive electromagnetic field propagation and ill-posed inversion processes in subsurface formations.
Innovation Solution
The magneto-seismic exploration method involves generating a time-varying electromagnetic field in the subsurface, interacting with a static or time-varying magnetic field to create Lorentz forces, which generate seismic signals that can differentiate between formations with varying conductivities, thereby improving spatial resolution and accuracy of conductivity mapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If conventional CSEM methods use low frequency electromagnetic fields to penetrate deep subsurface formations, then the electromagnetic field can reach deeper targets, but the spatial resolution of the resistivity maps deteriorates due to diffusive propagation and skin effect
Solution Approach 1:
The patent introduces a secondary magnetic field as an intermediary that interacts with the primary electromagnetic field to generate Lorentz forces. This intermediary mechanism converts electromagnetic energy into mechanical seismic waves, which propagate differently through the subsurface compared to pure electromagnetic diffusion, thereby improving spatial resolution while maintaining deep penetration capability
Solution Approach 2:
The patent replaces the conventional electromagnetic detection system with a magneto-mechanical system. Instead of directly measuring electromagnetic fields that diffuse through the subsurface, the system generates seismic waves through Lorentz forces and detects the mechanical response, substituting electromagnetic measurement with mechanical wave propagation for improved resolution
2Loss of information
If conventional seismic surveys are used to image subsurface structures, then the method can provide information about geologic layer structures, but it cannot reliably distinguish between hydrocarbon and brine formations due to similar seismic velocities
Solution Approach 1:
The patent merges two geophysical methods: electromagnetic surveying (which is sensitive to conductivity differences between hydrocarbon and brine) and seismic surveying (which provides structural information). By combining these methods into a unified magneto-seismic system, the invention simultaneously captures both conductivity contrast and structural information, enabling reliable hydrocarbon identification
Solution Approach 2:
The patent creates a composite geophysical measurement approach that combines electromagnetic and seismic measurement principles. The system uses both electromagnetic fields and magnetic fields together to generate and detect signals, creating a composite measurement system that exploits multiple physical properties (conductivity and mechanical impedance) to distinguish hydrocarbon from brine
3Manufacturing precision
If the frequency of the electromagnetic field from the source is increased to improve spatial resolution, then the skin depth decreases and electromagnetic fields attenuate faster in subsurface formations, limiting the achievable resolution for deeper targets
Solution Approach 1:
The patent employs dynamic, time-varying electromagnetic fields rather than static or single-frequency fields. By using time-varying fields that interact with the subsurface over multiple cycles, the system achieves better penetration and resolution than static electromagnetic methods, dynamically adapting the field characteristics to optimize both depth and resolution
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 the spatial resolution and accuracy of subsurface conductivity mapping, allowing for better differentiation between hydrocarbon and brine-saturated formations, overcoming the limitations of existing techniques by directly correlating conductivity differences with seismic responses.
Implementation Method 1
A time-varying electromagnetic field is transmitted into the subsurface, in the presence of a static or time-varying magnetic field, such that a component of an electric current associated with the time-varying electromagnetic field is substantially parallel to an interface between two subsurface formations... resulting differential Lorentz forces... generate a seismic signal
Implementation Method 2
electromagnetic radiation propagates diffusively in the subsurface
Implementation Method 3
The poor spatial resolution is due to the fact that electromagnetic radiation propagates diffusively in the subsurface... Diffusive propagation occurs because the Earth has a modest electrical conductivity giving rise to a skin effect phenomenon
Implementation Method 4
The resulting differential Lorentz forces may generate a seismic signal that may be detected by a seismic receiver
Data Source
AI summary
Systems and methods are provided for a magneto-seismic exploration of a subsurface region. An electromagnetic source may transmit time-varying electromagnetic field into the subsurface region, in the presence of a static or time-varying magnetic field, such that a component of the electric field associated with the time-varying electromagnetic field is substantially parallel to an interface between two subsurface formations in the subsurface region, wherein the electric field interacts with the static or time-varying magnetic field and creates a Lorentz force in each of the subsurface formations. One or more seismic receivers may detect a seismic signal generated by a Lorentz force change at the interface between the two subsurface formations. A computer system may be programmed to process and present the detected seismic signal.