The ICDP Lake Bosumtwi Drilling Project: A First Report

The 10.5 -km-diameter, 1.07-Ma Bosumtwi impact crater was the subject of a multi-disciplinary and international drilling effort of the International Continental Scientific Drilling Program (ICDP) from July to October 2004. Sixteen different holes were drilled at six locations within the lake, to a maximum depth of 540 m. A total of about 2.2 km of core material was obtained. Despite some technical and logistical challenges, the project has been very successful and it is anticipated that the first scientific results will be available in late 2005

SEISMIC MODELING OF HETEROGENEITY SCALES OF GAS HYDRATE RESERVOIRS

The presence of gas hydrates in permafrost regions has been confirmed by core samples recovered from the Mallik gas hydrate research wells located within Mackenzie Delta in the Northwest Territories of Canada. Strong vertical variations of compressional and shear velocities and weak surface seismic expressions of gas hydrates indicate that lithological heterogeneities control the lateral distribution of gas hydrates. Seismic scattering studies predict that typical horizontal scales and strong velocity contrasts due to gas hydrate concentration will generate strong forward scattering, leaving only weak energy to be captured by surface receivers. In order to understand the distribution of gas hydrates and the scattering effects on seismic waves, heterogeneous petrophysical reservoir models were constructed based on the P-wave and S-wave velocity logs. Random models with pre-determined heterogeneity scales can also be used to simulate permafrost interval as well as sediments without hydrates. Using the established relationship between hydrate concentration and P-wave velocity, we found that gas hydrate volume content can be determined by correlation length and Hurst number. Using the Hurst number obtained from Mallik 2L-38, and the correlation length estimated from acoustic impedance inversion, gas hydrate volume fraction in Mallik area was estimated to be 17%, approximately 7x108 m3 free gas stored in a hydrate bearing interval with 250,000 m2 lateral extension and 100 m depth. Simulations of seismic wave propagation in randomly heterogeneous models demonstrate energy loss due to scattering. With the available modeling algorithm, the impact of heterogeneity scales on seismic scattering and optimum acquisition geometries will be investigated in future studies.Non UBCUnreviewe

Appraisal of the Parameters of the Lithoprobe Abitibi-Grenville Seismic Reflection Survey

The 1990-1991 Lithoprobe Abitibi-Grenville seismic reflection survey comprises 989 km of regional data collected for crustal exploration and 81 km of high-resolution data collected for mineral exploration. A proper interpretation of the data requires an understanding of its limitations; these are a function of the acquisition parameters. The vertical resolution is ~38 m for the regional data and 15 m for the high-resolution data. The maximum reflector dip that can be imaged in shallow data is ~70°, but deep data are biased toward subhorizontal reflections. The principal sources of noise are vibrator truck noise, groundroll, and shear wave refractions. Power-line noise is surprisingly important on some high-resolution lines. The seismic signal penetrates to the Moho, revealing differences in Moho reflectivity across the survey. Résumé En 1990 et 1991, des données de sismique réflexion ont été enregistrées dans le cadre de la première phase du projet Lithoprobe Abitibi-Grenville. Plus de 989 km de levés régionaux permettant l'étude de la croûte terrestre et 81 km de levés à haute résolution pour l'exploration minière ont été réalisés. Une interprétation convenable des données doit tenir compte des limites imposées par les paramètres d'acquisition. La résolution verticale des levés régionaux est d'environ 38 m, tandis que celle des levés à haute résolution est de 15 m. La méthode permet de reconnaître des structures géologiques peu profondes dont les pendages sont inférieurs à 70°; le pendage maximum des structures imagées en profondeur est plus faible. Le bruit le plus important provient des ondes de surface et des ondes de cisaillement réfractées. Malgré l'utilisation d'un nouveau système d'acquisition atténuant le 60 Hz ambiant, ce bruit demeure important sur certains profils à haute résolution. La pénétration du signal sur la majorité des profils est suffisante pour atteindre la discontinuité de Mohorovicic, ce qui suggère que sa non-réflectivité a une signification géologique. Néanmoins, la structure de la croûte profonde doit être interprétée prudemment parce que la plupart des profils sismiques ont une longueur insuffisante pour imager correctement des structures inclinées à ce niveau

Enhancing base-metal exploration with seismic imaging

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