PASSIVE GEOPHYSICAL PROSPECTING APPARATUS AND METHOD BASED UPON DETECTION OF DISCONTINUITIES ASSOCIATED WITH EXTREMELY LOW FREQUENCY ELECTROMAGNETIC FIELDS

摘要

An apparatus (200) for passively determining the depth and thickness of a subterranean geologic formation bearing hydrocarbons. The apparatus has an antenna (12) to pick up extremely low frequency signals naturally emanating from the Earth's surface. The received signal is amplified and filtered and then modulated onto a carrier wave. The modulated signal is then filtered to eliminate one of the sidebands. An oscillator (16) 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. For each desired frequency within this range, the tuned signal is adjusted to the desired frequency and is sent to a voltage level detectoron and converting same to pulses. The pulses are counted over a desired time period to determine the pulse density.