Electric Resistivity Logging

Resistivity logging in the Gravberg 1 well shows an increase in electric resistivity within the top 1.2 km. It then stabilizes at relatively high values around 30 kOm. These loggings also indicate the occurrence of larger fracture zones, with a vertical spacing of 90 to 150 m throughout the drill hole. This is comparable to the results from airborne VLF data that indicate a similar lateral fracture spacing of 150 to 450 m within the whole central uplift region (Henkel 1992).

Resistivity logging in the Stenberg-1 well shows significantly more fracturing as recorded in the Gravberg-1 well. Porosity calculated from sonic and resistivity data shows a typical block size of alternating high and low porosity of 350 m. The top 1.5 km are heavily fractured throughout the central uplift with porosities of 2 to 4 %, occasionally approaching 20 %. Relatively fresh water with a salinity of 1 gl-1 was found down to 4.7 km depth, from where the salinity increased to 5 gl-1 at 5.4 km depth.

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