Method and Apparatus for Offshore Hydrocarbon Electromagnetic Prospecting Based on Total Magnetic Field Measurements
OwnerJostein Kåre Kjerstad, Eduard B. Fainberg +1inventors
InventorsJostein Kåre Kjerstad, Eduard B. Fainberg, Pavel Barsukov
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Abstract
A system for offshore hydrocarbon electromagnetic prospecting is described. The system includes a transmitter generating electromagnetic energy and injecting an electrical current into a flooded vertical cable. Electromagnetic fields generated by this current in the medium are measured by total field magnetometers or gradiometers. The measured response, which is sensitive to the resistivity of targets, is used to search for and identify hydrocarbon reservoirs. A method for offshore hydrocarbon electromagnetic prospecting is described as well.
Claims27
A system for the electromagnetic surveying of a hydrocarbon reservoir below a sea floor, the system includes
- a plurality of receivers (P) distributed on the sea floor, each receiver (P) being provided with a recorder device including a total-field magnetometer which is arranged to determine a medium's response to an electromagnetic field provided in the medium by an electrical current on a vertical transmitter cable (L) submerged in a mass of water;
- a controlled-source electromagnetic transmitter attached to the vertical transmitter cable (L) arranged to be submerged in the mass of water and arranged to provide an alternating magnetic field;
- and
- signal-processing means which are arranged to receive and process a signal from each of the receivers (P), the signal characterizing, at least in part, the apparent resistivity and the total resistance of the reservoir.
A method of marine sub-sea-floor hydrocarbon electromagnetic prospecting, the method comprising the steps:
- a) placing a plurality of receivers (P) spaced apart on a sea floor, each receiver (P) being provided with a recorder device including a total-field magnetometer which is arranged to determine a medium response to an electromagnetic field provided in the medium by an electrical current in a vertical transmitter cable (L) submerged in a mass of water;
- b) placing a controlled-source electromagnetic transmitter attached to the vertical transmitter cable (L) submerged in the mass over water above a structure which is thought or known to contain a subterranean hydrocarbon reservoir, in such a way that all the magnetometers (Pm and Pe, respectively) are placed on the sea floor, either along a line passing through the vertical transmitter cable (L) in the direction of the local magnetic meridian;
- that is to say, in a meridional setup;
- or along a line passing through the vertical transmitter cable (L) perpendicularly to the direction of the local magnetic meridian;
- that is to say, in an equatorial setup;
- c) obtaining from each receiver (P, Pm, Pe) the total magnetic field responses of electromagnetic fields excited by the transmitter;
- d) accumulating, processing and storing response functions relating to signals from the transmitter and characteristic electrical properties of the structure;
- and
- e) analysing the measurement data with the objective of searching for and identifying hydrocarbon reservoirs.
Dependencies are inferred from the claim text.