Gundalf: Marine Seismic Source Modelling Software Package

Gundalf is a state of the art Cloud-based seismic source modelling software package for Airguns, Sparkers, Boomers and Marine Vibrators. Source array computer modelling is an enormously cost-effective exercise given the cost of downtime of a seismic survey vessel for signature tests or concerns about the effects of drop-out on airgun arrays, for example. In the processing centre, simple knowledge of the acquisition geometry and gun types allows an accurate signature to be generated for sophisticated signature deconvolution, or predict potential impacts on marine life.

It has taken a number of years to refine understanding of the physics of seismic sources such as airguns to its current level but modelling now offers a genuine alternative to the very costly experimental approach or the uncertainties inherent in near-field extrapolation.

Gundalf™ is capable of modelling source arrays of up to 128 fully-interacting guns for all modern source types including the very latest Bolt eSource™ airguns. Linear superposition of sub-arrays or even individual guns as has often been used, is rejected in favour of full physical modelling. No scientific compromise is made here, the physics at the heart of Gundalf™ is even capable of modelling the phase locking observed in closely-interacting airguns right down to the edge of the bubble collision region. It contains arguably the most advanced physics of its kind anywhere.

Gundalf™ is rigorously calibrated against large datasets of signatures recorded in specialist facilities.

The system is available in two forms, Designer and Optimiser, both of which use the same state of the art physical modelling engine, plus an optional Alternative Sources add-on module.

Gundalf Designer

• Enables the geophysicist to model the signature of up to 128 fully interacting airguns in an array quickly and accurately.
• Includes all modern airgun types including Bolt eSource and Long Life, Sercel G and GI guns and sleeve guns (all trademarks noted) in its array construction palette.
• Simple graphical interface to add, edit or delete guns, change the depth of all guns, manipulate sub-arrays, zooming and numerous other shortcuts. Each gun can be individually set in position, gun type, volume and operating pressure allowing complete flexibility.
• Signature characteristics such as peak to peak, primary to bubble and bubble period, along with detailed amplitude spectral characteristics are produced on demand complete with model error bounds derived from calibration.
• Sophisticated handling of the surface reflection ghost and optionally the cable ghost using rough sea surface modelling.
• Import and export of signatures in both text and SEGY format.
• Import and export of arrays in text format allowing full arrays with symmetric sub-arrays to be built quickly and easily, (noting that all interactions are always used when actually modelling the array).
• Comprehensive array reports produced in standard pdf format including detailed graphics for the array geometry, maximum bubble radii, signature and amplitude spectrum and colour contour plots of inline and cross-line directivity and plan view directivity.
• Sophisticated drop-out analysis using a wide range of industry standard criteria in both the time and frequency domains with automatic identification of illegal drop-out combinations. Instant mobile-device compatible output visualization.

Gundalf Optimiser

All the features of Gundalf Designer, plus the following additional functionality:

• The capability of generating sophisticated Intranet reports describing the potential broadband environmental noise impact on marine mammal life. These reports include SPL and SEL plots, swept-depth and particle velocity contours and optionally allow for particular species using NOAA recommendations and include the current best advice available from marine regulatory authorities such as BOEM, EPBC and JNCC. The model output can be adjusted using built-in widely-used bathymetric models to take account of ducting.
• The unique ability to define an inventory of airguns and then using sophisticated global optimisation techniques, to design the best array 'ground-up' within the constraints of spectral flatness in a certain region, maximal primary to bubble ratio or a number of other optimisation criteria including specific geophysical objectives such as improving sub-basalt imaging. The resulting arrays are often far superior to those resulting from simple intuition. Under option, Gundalf™ can be requested to overdraw the inventory (i.e. use more airguns of a particular type than are available in the inventory) in which case, it will produce a report at the end of any airgun types it felt necessary to overdraw.
• The ability to improve an existing airgun array using the same advanced global optimisation techniques.
• Airgun array signature stability analysis to model the effects of sea-state and optionally pressure variations in the compressor.
• The ability to generate signature sweeps in theta-phi for ocean bottom work with airgun arrays.

Alternative Sources Module

Optional add-on for Optimiser for modelling a growing number of Sparker and Boomer sources and additionally, a generic modelling engine for Marine Vibrators:

• Models the far-field signature and amplitude spectrum with full array statistics with downloadable signatures in ASCII and SEGY formats.
• Ability to produce inline, crossline directivity plots and azimuthal directivity plots at specified fixed frequencies.
• Ability to generate full environmental modelling reports for Sparker and Boomer sources (this is not currently applicable to marine vibrators which apart from harmonics do not provoke any frequencies outside the sweep range).
• As with airguns, both single and multiple element modelling including pressure-field interactions is incorporated.

Background Physics

The physics behind the airgun modelling engine in Gundalf™ is based originally on Laws, Hatton and Haartsen, (1990), "Computer Modelling of Clustered Airguns", First Break, vol. 8, no. 9, (Sept.) which itself builds on earlier published contributions by Anton Ziolkowski, Svein Vaage, Gregg Parkes and Bill Dragoset supported by experimental work done by Tor Haugland, Mike Hall and others. The model solves a complex set of differential equations combining both heat transfer and dynamics.

Over the last 10 years, this has been incrementally refined with modifications to the physics by Les Hatton to handle the 'super-foam' region of colliding bubbles and also to handle innovations such as injector guns and the latest environmentally friendly eSource guns. Periodically over the years, the model has been calibrated against multiple measurements of both non-interacting guns and interacting clusters for all common gun types at a wide range of deployment depths. The model produces signatures within the experimental error of the measurements and accurately models the phase-locking of airgun clusters reported in the above paper.

The model is unconditionally stable for all airgun combinations no matter how close.

Alternative sources such as Sparkers, Boomers and Marine Vibrators are treated similarly. The Marine Vibrator component of the modelling engine includes base-plate pressure field interaction effects of multiple vibrators.

For more details and downloadable papers, see also www.leshatton.org.

Licensing

Gundalf™ is a cloud-based service running on dedicated compute-optimised servers in multiple geographic datacentres for optimum speed and availability from any location. It is platform-independent and can be run from a standard web browser. The system has additionally been optimised for low-bandwidth on-vessel connections.

Gundalf™ is a leased product, please contact us for a quotation »