PRELIMINARY RESULTS OF GEOTHERMAL INVESTIGATIONS IN THE BOREHOLE EYREVILLE-B, CHESAPEAKE PENINSULA

Boreholes drilled in impact structures are especially suited for investigations of the influence of impact induced heterogeneities on petrophysical properties and the thermal field. In the scientific well Eyreville-B drilled within the frame of the International Continental Drilling Program (ICDP) two high resolution temperature measurement campaigns and a dense petrophysical profile measured on core samples at ~10 m depth intervals were recorded. The temperature values of the first campaign in December 2005 were heavily disturbed by outflow of artesian water and can only be used for an estimation of the depth where the fluid originated. Only at the nearby borehole USGS test hole STP-2 an undisturbed temperature profile down to 700 m depth could be measured. For the second campaign in Mai 2006 a riser was constructed to enable measurements, without opening the wellhead, in the thermally equilibrated fluid of the well. This construction allowed measuring the undisturbed temperature profile as well as the relaxation process after some later outflow of artesian water which heated the surrounding rock. The temperature profiles from Eyreville-B and STP2 are investigated and compared. From the calculated vertical component of the thermal gradient and the thermal conductivity measured on the core samples a mean heat flow density of 65 +/- 6 mW/m^2 in the depth interval 440 - 1100 m was determined. This value is higher than previously reported values for this region. The consecutive measurements of the relaxation process yield an estimate of the in-situ values of the geothermal parameters.