Determining Geological Properties by a Hybrid Seismic-Magnetotelluric Approach

Geiger, Hugh and Lamoureux, Michael (2002) Determining Geological Properties by a Hybrid Seismic-Magnetotelluric Approach. Canadian Industrial Problem Solving Workshops > 6th IPSW [Vancouver 27/5/2002 - 31/5/2002].

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Abstract/Summary

This paper concerns the controlled source audio magnetotelluric technique (CSAMT) for imaging subsurface structure. Given the short time available, we limited our investigation to a simple 1D earth model where regional seismic and well logs suggest discrete layers, each with constant seismic velocity and constant electrical conductivity. In addition, the well logs provide rough estimates of velocity and conductivity for use as a starting point in the seismic and MT inversions.

Problem Statement

Of all the geophysical techniques, controlled-source refl
ection seismology is the preferred method for oil and gas exploration in the Canadian foothills, as it provides the best resolved images of structures at depth and can provide detailed information about subsurface rock properties such as elastic or acoustic impedance contrasts. Unfortunately, good quality seismic data cannot always be acquired over subsurface targets.

The controlled source audio magnetotelluric technique (CSAMT) is another viable geophysical tool for imaging subsurface structure. Unfortunately, electromagnetic waves propagating in conducting media satisfy the diffusion equation, and hence the best possible resolution of subsurface conductivity structure using the MT method is typically much worse than for seismic waves propagating in an elastic media. However, great strides have been made over the last decade in the acquisition, processing, interpretation and inversion of 2D and 3D MT data. It might therefore be possible to collect high quality MT data in areas where the seismic data are of poor quality, but several open questions remain:

1. Could MT help to better define the geology, in comparison to using a regional geological model, in areas of poor seismic?

2. Can a geological model be produced by joint tomographic inversion of both data types?

3. Which would be favourable conditions for the application?

4. What kind of computing power is likely to be involved?

5. Given the recent advances in the acquisition, processing, interpretation and inversion of MT data and the associated improvement in lateral resolution, is there an emerging opportunity to combine MT with seismic in areas of complex geology?

6. What are the theoretical and practical issues involved in combining surface seismic and surface MT data by joint tomographic inversion in areas where seismic alone cannot sufficiently explain the subsurface in the Canadian Foothills.

7. Is common inversion of seismic and magnetotelluric data an option for gas exploration in the heavy structured thrust belt environment of the Canadian Foothills?

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