Passive geophysical prospecting apparatus and method based upon detection of discontinuities associated with extremely low frequency electromagnetic fields
US5777478A · kind A · utility
Assignees
Inventor
Key dates
| Filing date | Aug 27, 1996 |
| Grant date | Jul 7, 1998 |
| Priority date | — |
| Expiry date | Aug 27, 2016 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01V3/12
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
An apparatus and method for passively determining the depth and thickness of a subterranean geologic formation bearing hydrocarbons, e.g., oil and/or gas, or commercially important ore deposits, e.g., precious metals. The apparatus has an antenna to pick up extremely low frequency signals naturally emanating from the Earth's surface. In a preferred embodiment, the received signal is amplified and filtered. The signal is then modulated onto a carrier wave. The modulated signal is then filtered to eliminate one of the sidebands, for example, the lower sideband. An oscillator generates a tuning frequency which is then beat against the filtered, modulated signal in order to tune to a particular frequency. The oscillator sweeps through the range of frequencies, e.g., in the upper sideband portion of the filtered, modulated signal. For each desired frequency within this range which corresponds to a certain depth in the Earth, the tuned signal is adjusted to the desired frequency and is sent to a voltage level detector for detecting the tuned information and converting same to pulses. The pulses are counted over a desired time period to determine the pulse density, i.e., number of pulses …
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.