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Abstract

The Famenne seismic campaign (1976-1978), which was carried out in the southern part of Belgium, east of the Meuse Valley, has identified a major subhorizontal reflector, marking an angular unconformity, which was thought to represent the Condroz Overthrust. The outcroup of this thrust fault to the north marks the front of the Variscan Orogeny.

The aim of the Havelange weIl was to reach the thrust fault and to determine wether the rockmass underneath was Caledonian or Hercynian, the latter possibility beeing not without economic interest.

The well starts within an Upper Devonian formation and then reachs Lower Devonian formations at 1920 m MD. These formations were found till the total depth at 5648 m MD. Palynological data showed the existence of three main faults, respectively at 4850 m MD, 4955 m MD and 5078 m MD. The position of these faults was controlled by different weIl geophysical data.

The present paper emphasizes the technical aspects of the drilling work, in connection with the geological formation constitution. The geological and geophysical data achieved are discussed.