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.

A B S T R A C TThis paper tests the ability of various rock physics models to predict seismic velocities in shallow unconsolidated sands by comparing the estimates to P and S sonic logs collected in a shallow sand layer and ultrasonic laboratory data of an unconsolidated sand sample. The model fits are also evaluated with respect to the conventional model for unconsolidated sand. Our main approach is to use Hertz-Mindlin and Walton contact theories, assuming different weight fractions of smooth and rough contact behaviours, to predict the elastic properties of the high porosity point.Using either the Hertz-Mindlin or Walton theories with rough contact behaviour to define the high porosity endpoint gives an over-prediction of the velocities. The P-velocity is overpredicted by a factor of ∼1.5 and the S-velocity by a factor of ∼1.8 for highly porous gas-sand. The degree of misprediction decreases with increasing water saturation and porosity.Using the Hertz-Mindlin theory with smooth contact behaviour or weighted Walton models gives a better fit to the data, although the data are best described using the Walton smooth model. To predict the properties at the lower porosities, the choice of bounding model attached to the Walton Smooth model controls the degree of fit to the data, where the Reuss bound best captures the porosity variations of dry and wet sands in this case since they are caused by depositional differences.The empirical models based on lab experiments on unconsolidated sand also fit the velocity data measured by sonic logs in situ, which gives improved confidence in using lab-derived results.

We have developed a procedure for estimating the effective elastic properties of various mixtures of smectite and kaolinite over a range of confining pressures, based on the individual effective elastic properties of pure porous smectite and kaolinite. Experimental data for the pure samples are used as input to various rock physics models, and the predictions are compared with experimental data for the mixed samples. We have evaluated three strategies for choosing the initial properties in various rock physics models: (1) input values have the same porosity, (2) input values have the same pressure, and (3) an average of (1) and (2). The best results are obtained when the elastic moduli of the two porous constituents are defined at the same pressure and when their volumetric fractions are adjusted based on different compaction rates with pressure. Furthermore, our strategy makes the modeling results less sensitive to the actual rock physics model. The method can help obtain the elastic properties of mixed unconsolidated clays as a function of mechanical compaction. The more common procedure for estimating effective elastic properties requires knowledge about volume fractions, elastic properties of individual constituents, and geometric details of the composition. However, these data are often uncertain, e.g., large variations in the mineral elastic properties of clays have been reported in the literature, which makes our procedure a viable alternative.