Electromagnetic surveying for hydrocarbon reservoirs

An electromagnetic survey method for surveying an area previously identified as potentially containing a subsea hydrocarbon reservoir, comprising:

• providing an electromagnetic source having a dipole axis and a first detector;
• obtaining first and second survey data sets by moving the electromagnetic source relative to the first detector to collect data over a range of source-to-detector distances and orientations,
• wherein the first survey data set is obtained with the dipole axis of the electromagnetic source aligned end-on relative to the first detector so that the first survey data set is sensitive to resistive hydrocarbon layers exploiting largely galvanic effects, and
• wherein the second survey data set is obtained with the dipole axis of the electromagnetic source aligned broadside relative to the first detector so that the second survey data set is relatively insensitive to resistive hydrocarbon layers exploiting dominantly inductive effects.

A method of planning an electromagnetic survey of an area identified as potentially containing a subsea hydrocarbon reservoir, comprising:

• creating a model of the area to be surveyed, including a rock formation containing a hydrocarbon reservoir and a body of water above the rock formation;
• setting values for water depth, depth below the seafloor of the hydrocarbon reservoir, and resistivity structure of the rock formation;
• performing a simulation of an electromagnetic survey in the model of the survey area by calculating first and second survey data sets by simulating an electromagnetic source having a dipole axis and first and second detectors and moving the electromagnetic source relative to each detector to collect data over a range of source-to-detector distances, wherein the first survey data set is obtained with the dipole axis of the electromagnetic source aligned end-on relative to the first detector so that the first survey data set is sensitive to resistive hydrocarbon layers exploiting largely galvanic effects, and wherein the second survey data set is obtained with the dipole axis of the electromagnetic source aligned broadside relative to the second detector so that the second survey data set is relatively insensitive to resistive hydrocarbon layers exploiting dominantly inductive effects;
• and
• combining the first and second survey data sets to obtain a results data set that represents a difference between the end-on and broadside alignments as a function of the source-to-detector distances.

A method of planning an electromagnetic survey of an area identified as potentially containing a subsea hydrocarbon reservoir, comprising:

• creating a model of the area to be surveyed, including a rock formation containing a hydrocarbon reservoir and a body of water above the rock formation;
• setting values for water depth, depth below the seafloor of the hydrocarbon reservoir, and resistivity structure of the rock formation;
• performing a simulation of an electromagnetic survey in the model of the survey area by calculating first and second survey data sets by simulating an electromagnetic source having a dipole axis and a first detector and moving the electromagnetic source relative to the first detector to collect data over a range of source-to-detector distances and orientations, wherein the first survey data set is obtained with the dipole axis of the electromagnetic source aligned end-on relative to the first detector so that the first survey data set is sensitive to resistive hydrocarbon layers exploiting largely galvanic effects, and wherein the second survey data set is obtained with the dipole axis of the electromagnetic source aligned broadside relative to the first detector so that the second survey data set is relatively insensitive to resistive hydrocarbon layers exploiting dominantly inductive effects;
• and
• combining the first and second survey data sets to obtain a results data set that represents a difference between the end-on and broadside alignments as a function of the source-to-detector distances.

A computer program product bearing machine readable instructions for implementing a method of planning an electromagnetic survey of an area identified as potentially containing a subsea hydrocarbon reservoir, comprising:

• creating a model of the area to be surveyed, including a rock formation containing a hydrocarbon reservoir and a body of water above the rock formation;
• setting values for water depth, depth below the seafloor of the hydrocarbon reservoir, and resistivity structure of the rock formation;
• performing a simulation of an electromagnetic survey in the model of the survey area by calculating first and second survey data sets by simulating an electromagnetic source having a dipole axis and first and second detectors and moving the electromagnetic source relative to each detector to collect data over a range of source-to-detector distances, wherein the first survey data set is obtained with the dipole axis of the electromagnetic source aligned end-on relative to the first detector so that the first survey data set is sensitive to resistive hydrocarbon layers exploiting largely galvanic effects, and wherein the second survey data set is obtained with the dipole axis of the electromagnetic source aligned broadside relative to the second detector so that the second survey data set is relatively insensitive to resistive hydrocarbon layers exploiting dominantly inductive effects;
• and
• combining the first and second survey data sets to obtain a results data set that represents a difference between the end-on and broadside alignments as a function of the source-to-detector distances.

A computer apparatus loaded with machine readable instructions for implementing a method of planning an electromagnetic survey of an area identified as potentially containing a subsea hydrocarbon reservoir, comprising:

• creating a model of the area to be surveyed, including a rock formation containing a hydrocarbon reservoir and a body of water above the rock formation;
• setting values for water depth, depth below the seafloor of the hydrocarbon reservoir, and resistivity structure of the rock formation;
• performing a simulation of an electromagnetic survey in the model of the survey area by calculating first and second survey data sets by simulating an electromagnetic source having a dipole axis and first and second detectors and moving the electromagnetic source relative to each detector to collect data over a range of source-to-detector distances, wherein the first survey data set is obtained with the dipole axis of the electromagnetic source aligned end-on relative to the first detector so that the first survey data set is sensitive to resistive hydrocarbon layers exploiting largely galvanic effects, and wherein the second survey data set is obtained with the dipole axis of the electromagnetic source aligned broadside relative to the second detector so that the second survey data set is relatively insensitive to resistive hydrocarbon layers exploiting dominantly inductive effects;
• and
• combining the first and second survey data sets to obtain a results data set that represents a difference between the end-on and broadside alignments as a function of the source-to-detector distances.

A computer program product bearing machine readable instructions for implementing a method of planning an electromagnetic survey of an area identified as potentially containing a subsea hydrocarbon reservoir, comprising:

• creating a model of the area to be surveyed, including a rock formation containing a hydrocarbon reservoir and a body of water above the rock formation;
• setting values for water depth, depth below the seafloor of the hydrocarbon reservoir, and resistivity structure of the rock formation;
• performing a simulation of an electromagnetic survey in the model of the survey area by calculating first and second survey data sets by simulating an electromagnetic source having a dipole axis and a first detector and moving the electromagnetic source relative to the first detector to collect data over a range of source-to-detector distances and orientations, wherein the first survey data set is obtained with the dipole axis of the electromagnetic source aligned end-on relative to the first detector so that the first survey data set is sensitive to resistive hydrocarbon layers exploiting largely galvanic effects, and wherein the second survey data set is obtained with the dipole axis of the electromagnetic source aligned broadside relative to the first detector so that the second survey data set is relatively insensitive to resistive hydrocarbon layers exploiting dominantly inductive effects;
• and
• combining the first and second survey data sets to obtain a results data set that represents a difference between the end-on and broadside alignments as a function of the source-to-detector distances.

A computer apparatus loaded with machine readable instructions for implementing a method of planning an electromagnetic survey of an area identified as potentially containing a subsea hydrocarbon reservoir, comprising:

• creating a model of the area to be surveyed, including a rock formation containing a hydrocarbon reservoir and a body of water above the rock formation;
• setting values for water depth, depth below the seafloor of the hydrocarbon reservoir, and resistivity structure of the rock formation;
• performing a simulation of an electromagnetic survey in the model of the survey area by calculating first and second survey data sets by simulating an electromagnetic source having a dipole axis and a first detector and moving the electromagnetic source relative to the first detector to collect data over a range of source-to-detector distances and orientations, wherein the first survey data set is obtained with the dipole axis of the electromagnetic source aligned end-on relative to the first detector so that the first survey data set is sensitive to resistive hydrocarbon layers exploiting largely galvanic effects, and wherein the second survey data set is obtained with the dipole axis of the electromagnetic source aligned broadside relative to the first detector so that the second survey data set is relatively insensitive to resistive hydrocarbon layers exploiting dominantly inductive effects;
• and
• combining the first and second survey data sets to obtain a results data set that represents a difference between the end-on and broadside alignments as a function of the source-to-detector distances.