Electromagnetic surveying for hydrocarbon reservoirs

A method of analysing results from controlled source electromagnetic surveying to monitor changes in a hydrocarbon reservoir, comprising:

• 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 at a first time;
• 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 at a second time;
• and
• comparing the VED response data from the first and second times to obtain difference data sensitive to changes in the hydrocarbon reservoir that have occurred between the first and second times.

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

• penetrating the hydrocarbon reservoir with a hydrocarbon-producing well;
• obtaining vertical electric dipole (VED) response data for the area from at least one VED detector detecting a signal from a horizontal electric dipole (HED) transmitter at a first time;
• extracting hydrocarbon from the hydrocarbon reservoir using the hydrocarbon-producing well;
• obtaining vertical electric dipole (VED) response data for the area from at least one VED detector detecting a signal from a horizontal electric dipole (HED) transmitter at a second time;
• comparing the VED response data from the first and second times to obtain difference data sensitive to changes in the hydrocarbon reservoir that have occurred between the first and second times;
• 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;
• obtaining vertical electric dipole (VED) response data for the area from at least one VED detector detecting a signal from a horizontal electric dipole (HED) transmitter at a first time;
• extracting hydrocarbon from the hydrocarbon reservoir using the hydrocarbon-producing well;
• obtaining vertical electric dipole (VED) response data for the area from at least one VED detector detecting a signal from a horizontal electric dipole (HED) transmitter at a second time;
• comparing the VED response data from the first and second times to obtain difference data sensitive to changes in the hydrocarbon reservoir that have occurred between the first and second times;
• 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 at least one VED detector detecting a signal from a horizontal electric dipole (HED) transmitter at a first time;
• obtaining vertical electric dipole (VED) response data for the area from at least one VED detector detecting a signal from a horizontal electric dipole (HED) transmitter at a second time;
• and
• generating the results data set based on the VED response data obtained at the first and second times.