georefid:2003-023442SEDIS Publication Catalogue

ana.macario@awi.de

http://sedis.iodp.org/pub-catalogue/informationpointOfContact2011-06-23T00:00:00Zhttp://sedis.iodp.org/pub-catalogue/index.php?id=2003-0234422001-01-01publicationgeorefid:2003-023442Pretzschner, CarstenFreiberg University of Mining and Technology, Freiberg, Federal Republic of GermanyauthorGoldberg, DaveLamont-Doherty Earth Observatory, United StatesauthorLindner, HaraldauthorGuerin, GillesauthorAmerican Association of Petroleum Geologists and Society of Economic Paleontologists and Mineralogists (AAPG), Tulsa, OK, United StatespublisherdocumentHardcopyIn: Anonymous, American Association of Petroleum Geologists 2001 annual meeting2001162Shear velocity logs in gas hydrate-bearing sediments were acquired for the first time along a transect of three ODP holes across the Blake Ridge. Shear wave data at Sites 995 and 997 indicate an increase in Vs in the presence of hydrate. Irregular borehole conditions at Site 994, however, did not allow Vs to be extracted using standard techniques. In this study, we use a statistical approach to identify shear waves by the local minimum of each waveform energy envelope. The resulting Vs profile is very similar to those at Sites 995 and 997, extending the observed increase in formation rigidity that is associated with the presence of hydrate beyond the lateral extent of the seismic BSR. In addition, we use these results to generate a 2-D tomographic inversion of the waveforms and determine the shear modulus distribution as a function of distance into the formation. The drilling process often influences measurements around a borehole due to invasion of fluids into the permeable formation. In the presence of hydrate, which is only stable under limited thermodynamic conditions, invasion is commonly thought to dissociate hydrate into free gas. At Site 994, however, the inversion suggests that hydrate does not decompose significantly due to fluid invasion into the formation. These results confirm that Vs logs can accurately measure the in situ properties of hydrate-bearing sediment and that hydrate deposits are not confined by the lateral extent of a BSR.completedEconomic geology, geology of energy sourcesApplied geophysicsaccuracyAtlantic OceanBlake-Bahama Outer Ridgebody wavesbottom-simulating reflectorsdrillingelastic wavesgas hydratesgeophysical methodsin situinverse problemLeg 164measurementnatural gasNorth AtlanticOcean Drilling ProgramODP Site 994petroleumpropertiesS-wavesseismic methodsseismic wavesthermodynamic propertiestomographytwo-dimensional modelsvelocitywaveformswell logsurn:org.iodp:exp:164urnlargerWorkCitationcampaignurn:org.iodp:exp:164:site:994urnlargerWorkCitationstudyurn:org.iodp:exp:164urnlargerWorkCitationcampaignEnglishgeoscientificInformation-75.3245-75.324531.470831.4708