Determining sea water resistivity
AssigneePGS Geophysical AS
InventorsTashi Tshering, Allan McKay, Johan Mattsson, Kathrin Flisnes Bergh
Life of this patent
Estimating the term…
Abstract
Methods of geophysical prospecting are described herein. In the described methods, a data set of electromagnetic readings from a marine geophysical survey is obtained and loaded into a computer processing system. Using the computer processing system, a high-frequency subset of the data is selected based on a frequency threshold, and a seawater resistivity map is resolved from the subset for a seawater portion of the survey by inversion. The seawater resistivity map can subsequently be used to resolve a resistivity map of the seabed from the data set by inversion.
Claims20
A method of geophysical prospecting, comprising:
- selecting a high-frequency subset from a data set of electromagnetic readings from a marine geophysical survey of a survey volume, the high-frequency subset including data having frequencies above a frequency threshold, the selecting comprising:
- generating a first model for the data set that comprises an air-water model;
- generating a second model for the data set that comprises the first model and includes effects of a seabed portion of the survey volume;
- and
- identifying the frequency threshold as a frequency above which the first model and the second model converge;
- inverting the high-frequency subset to resolve a resistivity map for a seawater portion of the marine geophysical survey;
- and
- storing the resistivity map for the seawater portion in a storage.
A method of marine geophysical prospecting, comprising:
- obtaining a data set of electromagnetic readings from a marine geophysical survey of a survey volume;
- selecting a high-frequency subset from the data set based on a frequency threshold, the selecting comprising:
- generating a first model for the data set that comprises an air-water model;
- generating a second model for the data set that comprises the first model and includes effects of a seabed portion of the survey volume;
- and
- identifying the frequency threshold as a frequency above which the first model and the second model converge;
- inverting the high-frequency subset to resolve a resistivity map for a seawater portion of the survey volume;
- saving the resistivity map for the seawater portion in a storage;
- using the resistivity map for the seawater portion to initialize an inversion model;
- and
- resolving a resistivity map for the seabed portion of the survey volume from the initialized inversion model and the data set using an inversion process;
- and
- saving the resistivity map for the seabed portion in the storage.
An improvement of a method of geophysical prospecting that includes obtaining an electromagnetic geophysical survey data set of a survey volume with a geophysical survey, loading the data set into a computer processing system, and resolving, by global inversion, resistivities of a seabed portion of the survey volume, the improvement comprising:
- using the computer processing system to perform a process of:
- selecting a high-frequency subset of the data set based on a frequency threshold, the selecting comprising:
- generating a first model for the data set that comprises an air-water model;
- generating a second model for the data set that comprises the first model and includes effects of the seabed portion of the survey volume;
- and
- identifying the frequency threshold as a frequency above which the first model and the second model converge;
- inverting the high-frequency subset to determine seawater resistivity to resolve a map of seawater resistivity from the inversion;
- and
- using the map of seawater resistivity to initialize the global inversion.
A non-transitory computer-readable medium containing a physical or magnetic pattern representing a data set depicting geologic features of a seabed volume made by a process, comprising:
- obtaining a data set of electromagnetic readings from a marine geophysical survey of a survey volume including the seabed volume;
- loading the data set into a computer processing system;
- and
- using the computer processing system to perform a computing process of:
- selecting a high-frequency subset from the data set based on a frequency threshold, the selecting comprising:
- generating a first model for the data set that comprises an air-water model;
- 'generating a second model for the data set that comprises the first model and includes effects of the seabed volume;
- and
- identifying the frequency threshold as a frequency above which the first model and the second model converge;
- inverting the high-frequency subset to resolve a resistivity map for a seawater portion of the survey volume;
- using the resistivity map for the seawater portion to initialize an inversion model;
- and
- resolving a resistivity map for the seabed volume from the initialized inversion model and the data set using an inversion process.
Dependencies are inferred from the claim text.