Electromagnetic surveying for hydrocarbon reservoirs

A computer program product bearing machine readable instructions for implementing a method of analyzing results from an underwater CSEM survey of an area that is thought or known to contain a subterranean hydrocarbon reservoir, comprising:

• providing electromagnetic field data obtained from an underwater controlled source electromagnetic (CSEM) survey at a plurality of discrete frequencies between 0.01 Hz and 60 Hz for specific source and receiver locations;
• performing a wavefield extrapolation of the data for the source and receiver locations for each of the plurality of frequencies so as to provide a corresponding plurality of distributions of electromagnetic scattering coefficient as a function of position and depth;
• and
• combining the distributions to provide an output map of electromagnetic scattering coefficient as a function of position and depth.

A computer apparatus loaded with machine readable instructions for implementing the method of analyzing results from an underwater CSEM survey of an area that is thought or known to contain a subterranean hydrocarbon reservoir, comprising:

• providing electromagnetic field data obtained from an underwater controlled source electromagnetic (CSEM) survey at a plurality of discrete frequencies between 0.01 Hz and 60 Hz for specific source and receiver locations;
• performing a wavefield extrapolation of the data for the source and receiver locations for each of the plurality of frequencies so as to provide a corresponding plurality of distributions of electromagnetic scattering coefficient as a function of position and depth;
• and
• combining the distributions to provide an output map of electromagnetic scattering coefficient as a function of position and depth.

A method of performing an underwater CSEM survey of an area that is thought or known to contain a subterranean hydrocarbon reservoir, comprising:

• providing at least one source and at least one receiver for transmission and detection of electromagnetic signals;
• obtaining electromagnetic field data with transmission and detection at a plurality of discrete frequencies between 0.01 Hz and 60 Hz for specific source and receiver locations;
• performing a wavefield extrapolation of the data for the source and receiver locations for each of the plurality of frequencies so as to provide a corresponding plurality of distributions of electromagnetic scattering coefficient as a function of position and depth;
• and
• combining the distributions to provide an output map of electromagnetic scattering coefficient as a function of position and depth.