Reverse semi-airborne electromagnetic prospecting
Method for semi-airborne electromagnetic prospecting for hydrocarbons or other fluids or minerals. In the method, electromagnetic receivers are deployed on the Earth's surface over a subsurface region ( 71 ). An airborne electromagnetic transmitter is flown over the receivers ( 72 ) and the receivers record at least one component of electromagnetic field data excited by the transmitter ( 73 ). The recorded electromagnetic data are analyzed for subsurface resistivity ( 74 ), and the resistivity is interpreted for evidence of hydrocarbons or other fluids or minerals ( 75 ). Compared to traditional fully airborne surveys, the advantages of the method include better signal-to-noise, and data for multiple source-receiver offsets.
1. A method for semi-airborne electromagnetic prospecting for fluids or minerals, comprising:
deploying a plurality of electromagnetic receivers on the Earth's surface over a subsurface region;
energizing an airborne electromagnetic transmitter in a vicinity above the receivers;
recording at least one component of electromagnetic field data excited by the transmitter in the receivers, wherein the electromagnetic transmitter transmits, and the receivers record, multiple frequencies for a single offset;
analyzing the at least one component of electromagnetic field data generated from the semi-airborne electromagnetic prospecting for subsurface resistivity; and
interpreting the resistivity for evidence of hydrocarbons.
2. The method of claim 1 , wherein the electromagnetic transmitter is a magnetic dipole.
3. The method of claim 2 , wherein the magnetic dipole is oriented either horizontally or vertically.
4. The method of claim 2 , wherein the magnetic dipole is oriented horizontally.
5. The method of claim 1 , wherein the electromagnetic receivers are directional magnetometers, measuring one or more vector components of magnetic field.
6. The method of claim 1 , wherein the transmitter and receivers are linked to a global positioning satellite for synchronization and location purposes.
7. The method of claim 1 , wherein the deploying of receivers is accomplished by one of (a) dropping from an aircraft; (b) lowering to the ground from an aircraft; and (c) placing by a ground-based operation.
8. The method of claim 1 , wherein the transmitter is towed above the subsurface region by an airplane or helicopter.
9. The method of claim 1 , wherein the receivers are deployed in a regular array.
10. The method of claim 1 , wherein the analyzing comprises inverting the recorded data to infer a resistivity model of the subsurface region.