Electromagnetic surveying for hydrocarbon reservoirs

A combined electromagnetic and seismic survey method applied to an area that is thought or known to contain a subterranean hydrocarbon reservoir, the area comprising subterranean strata beneath a seafloor, the method comprising:

• obtaining seismic data for the area;
• deploying at or above the seafloor a horizontal electric dipole (HED) transmitter and at least one receiver, the receiver including a vertical electric dipole (VED) detector;
• and
• collecting from the at least one VED detector VED response data induced by the HED transmitter.

A method for obtaining hydrocarbon from an area that contains a subterranean hydrocarbon reservoir, comprising:

• penetrating the hydrocarbon reservoir with a hydrocarbon-producing well;
• providing vertical electric dipole (VED) response data for the area obtained by at least one VED detector detecting a signal from a horizontal electric dipole (HED) transmitter;
• providing seismic data for the area;
• calculating a background model of the area from the seismic data;
• modelling an electromagnetic survey for the background model to provide background data specific to the area being surveyed;
• comparing the VED response data with the background data to obtain difference data sensitive to the presence of a subterranean hydrocarbon reservoir;
• and
• continuing to extract hydrocarbon from the hydrocarbon reservoir using the hydrocarbon-producing well.

A volume of hydrocarbon obtained from an area that contains a subterranean hydrocarbon reservoir, the hydrocarbon obtained by:

• penetrating the hydrocarbon reservoir with a hydrocarbon-producing well;
• providing vertical electric dipole (VED) response data for the area obtained by at least one VED detector detecting a signal from a horizontal electric dipole (HED) transmitter;
• providing seismic data for the area;
• calculating a background model of the area from the seismic data;
• modelling an electromagnetic survey for the background model to provide background data specific to the area being surveyed;
• comparing the VED response data with the background data to obtain difference data sensitive to the presence of a subterranean hydrocarbon reservoir;
• and
• continuing to extract hydrocarbon from the hydrocarbon reservoir using the hydrocarbon-producing well.

A results data set representing an area that contains a subterranean hydrocarbon reservoir, the results data set obtained by:

• obtaining vertical electric dipole (VED) response data for the area from by at least one VED detector detecting a signal from a horizontal electric dipole (HED) transmitter;
• providing seismic data for the area;
• calculating a background model of the area from the seismic data;
• modelling an electromagnetic survey for the background model to provide background data specific to the area being surveyed;
• comparing the VED response data with the background data to obtain difference data sensitive to the presence of a subterranean hydrocarbon reservoir;
• and
• generating the results data set based on the difference data.