Amplitude versus offset (AVO) inversion provides direct evidence for the presence of light oil in high-porous chalk in the South Arne Field, North Sea. The elastic properties of the chalk were estimated at three scales by analysing core data, log-readings and AVO-inversion results. The velocity–porosity relation of the core data matches a modified upper Hashin–Shtrikman model for Ekofisk Field chalk and the model is extended to 45% porosity. A small clay content reduces porosity without affecting chalk stiffness and this content can be estimated from the water saturation, which is controlled by silicate content and particle sorting in the zone of irreducible water saturation. The model is, thus, scaled according to clay content estimated by the water saturation. Based on comparison with the model and measurements on core samples, it is found that the sonic log data represent chalk characterized by forced displacement of the oil by mud filtrate and, thus, a much higher water saturation than estimated from, for example, a shallow resistivity log. Forward modelling of the acoustic properties of the virgin zone results in a characteristic pattern of Poisson ratio versus depth. This pattern agrees with inverted seismic data, whereas it is not captured by conventional fluid substitution.

The development ofmethodso fseismic imagingb eneathb asalts iss till hindered byalack of knowledge about the elastic propertiesofbasaltic sequencesandthe degree ofthree-dimensionalheterogeneity. The SeiFaBa project (2002)(2003)(2004)(2005)isfunded bythe SindriGroup aspart ofthe programmesfor licenseeswithin the Faroesearea andwill attempt to address theseissues.The Glyvursnes-1well wasdrilled bySeiFaBa through the UpperBasalt Formation outside Tórshavn in2002. Afull coreandnumerous wirelinelogswereacquired from the 700 mdeepwell. Duringthe sameoperations,the existing660 mdeepVestmanna-1well drilled mainly into the MiddleBasalt Formation wasreamed andlogged. The two wells arec entralt oanumbero fc losely co-ordinated experiments,which area ll targeted atcreating models for seismic wavepropagation through asuccession ofbasalt bycombiningdetailed analysisatcore, log andseismic scales. Datafrom thesetwo wells,incombination withthe datafor the Lopra-1well drilled into the LowerBasalt Formation,will givenewstratigraphic andpetrophysicalcontrol ofthe Lower,MiddleandUpper Basalt formations on the Faroes.The seismic programmewasinitiated in2002 andthe mainacquisition wascarried out during2003. The well siteatGlyvursnesgivesoptimalconditions for combiningVSP, offset-VSPandsurface seismic experimentsboth onshorea ndoffshorea ndthe seismic effects ofanearbyn ear-verticals hearz onec anbe studied indetail. Preliminary analysisoflogdatafrom the Lopra-1well suggests thatthe acoustic propertiesofthesebasalt flows aremainly controlled byporosity ofastiff matrixfilled withclayminerals andwater. Furtherstudieswill allow for explanations ofthe sonic responseofb asalt int erms ofphysicalandc ompositionalp ropertiesandabetter understandingofthe seismic signaturesoffloodbasalt successions.

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We have seismically characterized a Triassic-Jurassic deep geothermal sandstone reservoir north of Copenhagen, onshore Denmark. A suite of regional geophysical measurements, including prestack seismic data and well logs, was integrated with geologic information to obtain facies and reservoir property predictions in a Bayesian framework. The applied workflow combined a facies-dependent calibrated rock-physics model with a simultaneous amplitude-variation-with-offset seismic inversion. The results suggest that certain sandstone distributions are potential aquifers within the target interval, which appear reasonable based on the geologic properties. However, prediction accuracy suffers from a restricted data foundation and should, therefore, only be considered as an indicator of potential aquifers. Despite these issues, the results demonstrate new possibilities for future seismic reservoir characterization and rock-physics modeling for exploration purposes, derisking, and the exploitation of geothermal energy as a green and sustainable energy resource.

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