Pgs Geophysical as

Johan Mattsson

Peter Lindqvist

Robert Andras Juhasz

Carl Joel Gustav Skogman

Lars Erik Magnus Björnemo

Allan McKay

Tashi Tshering

Leif Abrahamsson

Erik Björnemo

Kathrin Flisnes Bergh

Jenny-Ann Malmberg

Tryggve Sørensen

Inversion of enhanced-sensitivity controlled source electromagnetic data can include combining measured controlled source electromagnetic (CSEM) data onto a common set of virtual receiver positions for each of a plurality of positions of a source along a survey path, determining a steering vector that enhances a sensitivity of the measured CSEM data to a subsurface resistivity variation, and performing an inversion using the measured CSEM data and modeled CSEM data, each having the steering vector applied thereto as a data weight, to better identify the subsurface resistivity variation.

Inversion of enhanced-sensitivity controlled source electromagnetic data

Electromagnetic (EM) inversion includes determining an electric field associated with EM data within a predetermined sensitivity area around each of a plurality of source positions, iteratively inverting the electric field for a subsurface resistivity EM model indicative of a subterranean formation for each of a plurality of EM electrical resistivity data cells within each of the predetermined sensitivity areas, and storing results of the iterative inversion. A linear system of equations comprising a Jacobian matrix is generated based on the iterative inversion, the linear system of equations is stored, and the linear system of equations is solved at each iteration of the iterative inversion to update the subsurface resistivity EM model until a convergence criterion is met. A resistivity map based on the updated subsurface resistivity EM model can be produced.

Electromagnetic data inversion

A method and apparatus for a streamer having a total field magnetometer ('TFM'). A streamer includes a plurality of TFMs in proximity with one another and distributed symmetrically about an axis of the streamer. A streamer includes a first subset of TFMs in a streamer section and in proximity with one another; a second subset in the streamer section and in proximity with one another; wherein the first subset is not in proximity with the second subset. A method includes towing a streamer through a body of water, the streamer comprising first and second TFMs; acquiring magnetic data with the first and the second TFMs; and reducing noise in the data based on at least one of: averaging data from the first and the second TFMs; filtering data from the first and the second TFMs; estimating motion of the first TFM; and estimating rotation of the first TFM.

Noise reduction for total field magnetometer measurements

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.

Determining sea water resistivity

A method and system for estimation of electromagnetic earth responses in a marine electromagnetic survey. A method may comprise estimating initial values of the electromagnetic earth responses and ambient noise applicable to the marine electromagnetic survey; and processing electromagnetic data based on the initial values of the electromagnetic earth responses and the ambient noise to obtain a joint estimation of updated values of the electromagnetic earth responses and the ambient noise, wherein the electromagnetic data was acquired with one or more electromagnetic sensors, wherein the electromagnetic data contains measurements of an electromagnetic field.

Joint estimation of electromagnetic earth responses and ambient noise

A resistivity profile can be generated directly from measured electromagnetic field data from a marine survey. A series of transformations can be applied to remove a conductivity dependency from a boundary value problem such that an inversion method may no longer be required to generate the resistivity profile.

Direct resistivity determination

Disclosed are apparatus and methods for determining characteristics of a target region which is embedded in background material below a body of water. In accordance with one embodiment, a resistivity background is determined. In addition, characteristics of an electric dipole due to the target region are determined. A resistance for the target region is then computed using the characteristics of the electric dipole and the resistivity background. Other embodiments, aspects and features are also disclosed.

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Trångsund, Sweden

Johan Mattsson