Geosciences
- An estimated Poisson's ratio from a prestack GA inversion of data.
- Schlumberger GeoQuest's GeoFrame SIP.
OB hydrophone and geophone processing
CGG's Robert Soubaras presented an interesting new perspective on "Ocean bottom hydrophone and geophone processing" at the recent SEG annual meeting in Denver. He noted that such measurements are usually processed by scaling the geophone component and summing it to the hydrophone. The output is supposed to be free of receiver ghost and peg-leg multiples. Calibration, deghosting, and peg-leg removal is done in one pass. These methods are, in fact, based on the modeling of the water bottom. Soubaras showed that a three-step procedure is preferable. First the geophone must be calibrated and a special function can be used for this. Second, a deghosted output must be computed, not by just summing the hydrophone and the calibrated geophone, but with a matched filter in order to attenuate the noise as well. The peg-legs can then be removed from the deghosted output in a manner similar to predictive deconvolution on conventional seismic data. The procedure showed how the steps of calibration and deghosting can be based on the modeling of the water surface and a finite duration assumption on the seismic source. The modeling of the water bottom layer, its reflectivity, for example, as well as the whiteness assumption on the earth, are needed only for the peg-leg attenuation.Genetic algorithm inversion model-building
Western Geophysical's Subhashis Mallick presents geoscientists with the technique of genetic algorithms (GA) that returns to the basics to define subsurface parameters. GA inversion is a statistical optimization process that generates a random population of elastic earth models within a specified search interval in the model space. Synthetic data are computed for each of the random models using an accurate wave-equation-based computation technique. A complete seismic response, including transmission loss, multiple reflections, and mode conversions is produced. Both reflection turning and propagation effects are accurately modeled. By using the GA inversion, synthetic data from the random models are compared with the observed data to obtain a fitness value for each model. After the comparison, genetic operations of reproduction, crossover, mutation, and update are done to produce new generations of models in an iterative process until the fitness values converge. Suitably chosen fitness values for each generated model are stored in the model space. At the end of the run, these values are normalized to obtain probable densities based on prior knowledge of the output (PPD) A complete elastic earth model can then be obtained by interpreting the PPD plots either automatically or manually.Geoteam adds Geo Arctic to North Sea
Geoteam, Norway, has chartered the Akademik Nametkin for 2D seismic work in the North Sea. The 82-meter vessel, renamed the Geo Arctic, was chartered from Arctic Marine Geological Expedition of Murmansk, Russia and is now being refitted in Norway. Upon completion, the vessel will carry a state-of-the-art 2D seismic acquisition system with 6,000 meter digital 24 bid streamer/recording system and 2890 cu. in. source based on Sodera G-guns. The Geo Arctic will be engaged in proprietary and non-exclusive work in the North Sea.New contract goes to GeoQuest/Omnes GeoQuest and Omnes have been awarded a three-year contract to provide geoscience and data management software, desktop computer hardware, and software support, as well as field communications for Triton Energy's 18 offices worldwide. GeoQuest's reservoir characterization and data management applications and Omnes' IT and communications systems are at the core of the contract.
POSC-compliant Beta SIP for WWW
Schlumberger's GeoQuest has produced an experimental, Internet WWW-based, POSC-compliant software integration platform called Beta SIP, a prototype environment for evaluating methods of integration of POSC standards into the GeoQuest products that can be executed via remote PC from anywhere on the world wide web network. GeoFrame SIP, from GeoQuest, is an open software integration platform supporting reservoir characterization applications and reservoir simulation and management aplications in a POSC-compliant working environment for storing and retrieving data. It allows geoscientists and reservoir engineers to manage, visualize, process, interpret, and model data, covering a broad spectrum of the E&P lifecycle.Gravity seismic combo for velocity verification
LCT has developed what it calls a Seismic Velocity Verification System (SVVS) in consortium with CGG-Petrosystems. The system involves a combination of gravity and seismic data to improve long wavelength velocity models in seismic processing. Via interpretation, important lithologic information can be determined from the final velocity, reflector geometry, and density models. Such gravity-derived velocity models can be used in the pre-stack depth migration process to provide the means of a rapid, more accurate, and cost-effective solution. The project is ongoing, with an aim to complete the integration of the SVVS (LCT) and PetroCaem (Petrosystems) software, as well as the establishment of numerous tools for modeling 2D and 3D data.Digicon upgrading to meet US Gulf demand
Digicon Geophysical is upgrading itself for the renewed emphasis on the US Gulf. The company's Seismic vessel Polar Search has been fitted with quad 7,500 meter streamers, and was recently deployed for a long offset deepwater shoot. The company has also undergone a $30 million update of its recording systems, added Syntron 24-bit data acquisition modules and RDA cables, and a NEC SX4 super computer, which will enable Digicon to carry out standard pre-stack time migrations of its deepwater data.UK's Ensign opens US offices
Ensign Geophysics, the UK-based 3D seismic processing specialist, has expanded to the USA, with a regional office in Houston having the same capabilities as the UK head office. Facilities include a scaleable IBM SP2 computing system configured with the latest thin P2SC (480 Mflop) nodes and Ensign's own parallel applications software. Installation and start-up is to be completed this month.Copyright 1997 Oil & Gas Journal. All Rights Reserved.