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  • Product Sheet: Seismic Coupling

Seismic coupling risk map

 

Seismic coupling risk map (Source: WesternGeco)

PRODUCT DESCRIPTION

Category

Component products

Integrated Product

 

  • Lithology features
  • Geomorphology map
  • Slope stability (geo-hazards, slope face creep); slope enhanced geomorphology map
  • Soft ground
  • Terrain roughness
  • Slope, curvature, aspect

 

Uses

  • Seismic Planning - Areas of poor coupling
  • Lithology, geology and structural properties of the near surface

Geo-information requirements

  • Terrain information
  • Topographic Information

Description

Vibroseis trucks are the most common form of seismic source in land surveys. These trucks move to shot points and the operator lowers the vibrator baseplate to place it in contact with the ground. The entire weight of the truck is then lifted onto this plate. The seismic signal is then sent into the ground by the action of the cylinders which exert force on the baseplate. It is important to maintain good contact with the baseplate and the earth’s surface, this is known as coupling. The quality of the recorded signal depends to a large extent on the baseplates contact with the ground. In addition to good contact, the surface needs to support the weight of the truck on the baseplate at each shot point.

A seismic coupling risk map is an integrated EO product that maps locations/areas that will be potentially a problem for coupling the base plate with the surface. Vibroseis operations are trying to achieve full and firm contact with the ground.

Managing this risk permits maximum vibrator quality data to be achieved in the field. This is monitored by sensors mounted on the shaker and the baseplate. If the baseplate is not coupled with the ground then it is no longer possible to transmit high fidelity vibrations into the ground. On soft ground, if the baseplate cannot be supported, it will break through the surface. This causes the controller to compensate by increasing the signal force which results in increased distortion of the emitted signal.

This integrated product is a cost map that aligns risk associated to each mapped feature mapped. A seismic coupling risk map will help geophysicists understand and plan for areas where the quality of the seismic signal will be impacted. The survey can be adjusted with offset points or infill to maintain the fold required by the client.

EO products such as soft ground mapping, lithology mapping and roughness mapping are the main inputs into the coupling risk map. These products provide a first look at the surface and can therefore help with planning mitigating the risk of point loading.

Known restrictions / limitations

  • Cloud cover would be a limitation on the optical data, most commonly in tropical areas, however archive imagery should provide mitigation against this.
  • Seasonality will have an impact so it is important for the user to understand when the image was acquired and the preceding weather conditions.
  • In dense vegetation where bare earth models are needed EO derived products cannot provide a solution.
  • Elevation data is limited by the availability of DEM data. DEM data derived from stereo pairs can have a lead time of 3 weeks, but this has a higher degree of accuracy than freely available lower resolution DEM’s. Radar derived DEM data available off-the-shelf, with accuracy affected in steep mountainous regions and densely vegetated regions.

Lifecycle stage and demand

Pre-licensing

Exploration

Development

Production

Decommissioning

 

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Exploration:

  • Seismic coupling risk mapping only effects the exploration part of the lifecycle. The role is to aid the land seismic operation, to ensure the data is of the highest quality, that the survey is undertaken in the safest possible way and the highest efficiency is achieved for the seismic contractor.  

Geographic coverage and demand

Global coverage (with a few restrictions see below). Demand in remote regions is high with exposed non vegetated surfaces best suited.

CHALLENGES ADDRESSED

OTM:043 Anticipating areas of high seismic impedance

OTM:058 Identifying ground conditions susceptible to poor coupling

 

HC:1103 Identify soft and hard ground as areas of potentially poor source and receiver coupling

PRODUCT SPECIFICATIONS

Input data sources

Optical: VHR1, VHR2, HR1, HR2, MR1

Supporting data:

  • Digital elevation models (DEM)
  • Existing  GIS data such as infrastructure and assets
  • Local knowledge

Spatial resolution and coverage

Spatial resolution: 1 m – 90 m pixel size

Minimum Mapping Unit (MMU)

Variable, but a 4 pixel area for Landsat data gives 3.6 km2 MMU

For optical satellite data with 0.5m spatial resolution this can be for example a MMU of 4 m².

Accuracy / constraints

Thematic accuracy: 80-90%

Spatial accuracy: The goal would be one pixel, but depends on reference data

Accuracy assessment approach & quality control measures

Stratified random points sampling approach utilizing in-situ measurements and any available published data or reports. Statistical confusion matrix with user’s and producer’s accuracy as well as kappa statistics for hydrological network and catchment area mapping.

Frequency / timeliness

Observation frequency: Archive data can be used although new acquisition may be a requirement in some situations. The frequency is constrained by client needs, satellite revisit and acquisition, but also processing requirements. Depending on the requirements of the customer the best suitable satellite sensor has to be chosen regarding spatial / spectral resolution as well as revisit frequency.

Timeliness of delivery: Delivery in time with project planning requirements. Archive data can be used to good effect if the prevailing conditions are known and the time of year is accounted for.

Availability

Archive data

On-demand acquisition

Delivery / output format

Data type:

  • Raster formats

File format:

  • Geotiff (standard - any other OGC standard file formats)

 Download Product Sheet

 

 

Lead Author:WesternGeco
Peer Reviewer:Hatfield Consultants

Author(s):

Andrew Cutts

Document Title:

Seismic coupling risk map

# of Pages:

4

Circulation:

Internal – Project consortium and science partners

 

External – ESA

 

 

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