Gravimetry

Gravimetry is the science of the Earth’s gravimetric field. The gravimetric field is sensitive to subsurface density variation. Density is rock property which constrains the geology and tectonic/geologic evolution. The method is described through potential field theory, in which the data are spatial derivatives of gravimetry potential. Potential field methods are inexpensive, but of low resolution and suffer from non-uniqueness. In practical applications, gravimetry must always be supported by additional information. The method is the oldest and most established geophysical technique that has long tradition in mining technology. In oil and gas industry, gravimetry is used for quick and inexpensive low-resolution mapping of large areas in frontier exploration.

Work Flow

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Introduction:

General Workflow:

Gravimetry acquisition:

Satellite missions:

• Low resolution, global coverage

• Suitable for studies of temporal global field variations

• Suitable for regional geologic modelling and interpretation

Airborne/marine acquisition:

• Medium resolution, relatively quick
• Suitable for regional to local geologic studies
• Most used for oil and gas industry and mining
• Used in frontier exploration (prior to seismic)

Terrestrial acquisition:

• High resolution, low coverage
• Suitable for local studies
• Application in engineering and near surface application (cavity detection, unexploded ordnance - UXO - detection).

Gravity anomalies:

Free-air anomaly

Bouguer anomaly

Isostatic anomaly

Gravimetry techniques:

2D forward modelling

Inversion

Free-air anomaly: The free-air correction is the amount that must be added to measurement at height h to correct to the reference level.

Bouguer anomaly: The Bouguer correction is the amount corrected for the height and the attraction of the terrain (free-air corrected and terrain corrected).