Physical Rock Properties and the Geothermal Field of the Chesapeake Bay Impact Structure
Zusammenfassung der Projektergebnisse
Investigations using 497 Eyreville cores (Chesapeake impact structure, USA) have been carried out in order to derive physical property logs for the complete section, for lithological and petrophysical interpretation and to investigate the influence of the impact on the physical properties at lithological scale. Since no logs (besides gamma and temperature) are available, the laboratory measurements on densely sampled rocks present a possibility of obtaining information about porosity, density, velocity, thermal properties for the interpretation of geophysical field data. Main factors controlling physical properties are porosity, mineralogical composition, structure of rocks e.g. fractures, grain contacts and the micromorphology. These factors differ considerably for the different lithological units. In the Postimpact sediments the high porosity (40 - 60%) is mainly controlling the physical properties. The Exmore sediment clast breccia and Exmore sediment megablocks (porosity 27 - 44%) display relatively small variations in all physical properties but are inhomogeneous on core scale. In the low porosity Granite section the physical properties indicate a subdivision. The porosity in the Suevite and Lithic Breccia section varies between 1% and 25%. Corresponding to these variations and to differences in grain contacts and heterogeneity (mineralogical composition) the section is inhomogeneous in borehole and core scale. The section below 1555m (porosity 1% - 13%) is inhomogeneous, too. The physical properties of these rocks (schists, pegmatites) are influenced by the lithology, the geological pre- impact history and the impact itself. A comparison between petrophysical properties of impactites for four different meteoritic impact structures, Puchezh-Katunk, Ries, Chicxulub and Chesapeake, reveals significant similarities but also some differences, depending on the different target rocks and on the position of the borehole within the crater. The suevites of three impact structures – Puchezh-Katunk, Ries and Chicxulub - have similar values of thermal conductivity. This can be explained by the fact that these suevites are characterized by high porosity and different deformation processes, caused by the impact load, which dominate over the differences in mineralogical and chemical compositions. Elevated values of thermal inhomogeneity factor of Suevite are characteristic for the Chesapeake, Chicxulub and Ries impact structures, demonstrating that the impact complex has larger micro- heterogeneity on core scale. In cases, where the target lithology is more or less homogeneous and the borehole is in the center of the crater (Puchezh-Katunk and Ries) the physical properties of the target rocks can be correlated to shock metamorphism. Two temperature logging campaigns have been performed in the ICDP-CBIS borehole Eyreville (November 27 – December 12, 2005 and May 1 – May 8, 2006). Due to the collapse of the open hole section of the well after removing the NQ-rods, temperature could only be logged down to 1100 m depth, but an equilibrated temperature profile could be measured in the USGS-borehole STP-2 nearby. In addition, the temperature profiles measured during the first campaign were heavily disturbed by artesian outflow of water. In order to prevent this outflow, a riser was conceived and constructed. After insertion of this tool in the borehole it was possible to measure nearly undisturbed temperature profiles during the second campaign. The obtained temperature profiles are, however, not precise enough to allow for a detection of a paleoclimatic signal. On the other hand, an anthropogenic signal was identified in the temperature profile, measured in the nearby USGS borehole STP-2. As it was not possible to measure thermal conductivity on the post-impact sediment samples within the depth interval 127 – 438 m, the temperature gradient could only be determined in the depth interval 438 – 1100 m, i.e. with the sediment-clast breccia interval. With the corresponding values of the measured thermal conductivity a local terrestrial heat flow value of 65 +/- 6 mW/m2 has been determined. In-situ parameters (equilibrated temperature and thermal conductivity) could be evaluated from the relaxation process of the borehole Eyreville after a 21.5 h controlled outflow of artesian water. Different approximations to the original thermal model equations, describing the temperature relaxation process after a thermal disturbance in the borehole, were used to investigate the measured temperature data. The choice of the input data set used is significant and shows the limitation of the model assumptions.
Projektbezogene Publikationen (Auswahl)
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(2006): First Geothermal Measurements in the ICDP Chesapeake borehole (Eyreville, Virginia). ICDP-IODP Joint Meeting, Greifswald, March 27-29, 2006
Heidinger P., Wilhelm H., Burkhardt H., Šafanda J.
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(2007): Physical Rock Properties of the Borehole Eyreville – Measurements and preliminary interpretation TOPICAL SESSION, GSA Denver Annual Meeting 2007 (28 - 31 October 2007)
Mayr S., Burkhardt H., Popov Y. and Wilhelm H.
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(2007): Preliminary results of geothermal investigations in the borehole Eyreville-B, Chesapeake Peninsula TOPICAL SESSION, GSA Denver Annual Meeting 2007 (28 - 31 October 2007)
Heidinger P., Wilhelm H., Popov Y., Šafanda J., Burkhardt H., and Mayr S.
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(2007): Thermal properties of rocks from the borehole Eyreville-B, Chesapeake Peninsula (Preliminary data) TOPICAL SESSION, GSA Denver Annual Meeting 2007 (28 - 31 October 2007)
Popov Y., Korobkov D., Romushkevich R., Gorobtsov D., Burkhardt H., Mayr S. and Wilhelm H.
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(2008) Geothermal investigations from well data of the Chesapeake Peninsula. IODP/ODP Joint Meeting - Euro-Forum Hannover, 12.-14. March. 2008
Heidinger P., Wilhelm H., Šafanda J., Burkhardt H., Mayr S., Popov Y.
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(2008) Interpretation der mechanischen und thermischen Eigenschaften verschiedener Bohrkerne aus den Chicxulub und Chesapeake Meteoriten-Einschlagskratern. FKPE Workshop Bohrlochgeophysik 2008 Hamburg, 8.-9. May
Mayr, S.
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(2008): Anthropogenic component of the subsurface temperature field: observed and synthetic examples. Geophys.Res.Abstr., Vol.10, 2008, EGU General Assembly 2008, 1607-7962/gra/EGU2008-A-03818, Wien, April 13-18, 2008
Dědeček P., Šafanda J., Heidinger P., Kukkonen I. and Rajver D.
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(2008): Geothermal investigations in superdeep and deep scientific wells: methods and results. EGU assembly, Vienna, Austria 13-18. April 2008
Popov Y., Burkhardt H., Wilhelm H., Romushkevich R., Mayr S., Heidinger P.
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(2008): Physical Rock Properties of the Chesapeake Bay Impact Structure. IODP/ODP Joint Meeting - Euro-Forum Hannover, 12.-14. March. 2008
Mayr S.I., Popov Y., Burkhardt H., Gorobtsov D.N., Romushkevich R.A.. Wilhelm H., Heidinger P.
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(2008): Thermal property measurements in studying heat and mass transfer processes in crust. EGU assembly, Vienna, Austria 13-18. April 2008
Popov Y., Burkhardt H., Wilhelm H., Tertychnyi V., Romushkevich R., Mayr S., Heidinger P.
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(2009). First results of geothermal investigations, Chesapeake Bay impact structure, Eyreville core holes. Geological Society of America Special Paper 458, pp.1-10
Heidinger, P., Wilhelm, H., Popov, Y., Šafanda, J., Burkhardt, H., Mayr, S.
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(2009). Physical rock properties of the Eyreville core, Chesapeake Bay impact structure. Geological Society of America Special Paper 458, pp.133-159
Mayr, S.I., Burkhardt, H., Popov, Y., Romushkevich, R., Miklashevskiy, D., Gorobtsov, D., Heidinger, P., Wilhelm, H.
