| Title | Seismic While Drilling Measurements in Italian Deep Geothermal Wells |
|---|---|
| Authors | Fausto Batini, I. Dini, Mario Certo, Tiziano Cola, Fabio Cecconi, Louis Soulier, Charles Naville and Sylvain Serbutoviez |
| Year | 2000 |
| Conference | World Geothermal Congress |
| Keywords | geothermal, Seismic While Drilling, SWD, MWD, EMWD, Larderello field |
| Abstract | The development of energy production from the main Italian geothermal fields (Larderello and Mt. Amiata) is closely correlated with the exploration of high enthalpy reservoirs in a very complex geological structure. Usually a cluster of geothermal wells is drilled from the same site in order to reach high temperature (>350 ?C) reservoirs in metamorphic rocks (some 3500 m below surface). Well Seismic Profiling (WSP) plays a very important role in the interpretation of the data supplied by reflection seismics when exploring such deep geothermal reservoirs, since the thermal conditions and seismic noise in geothermal wells drastically limit any conventional well seismic measurement. A multidisciplinary project (partially supported by the European Union) is currently in progress. The project combines the application of the following innovative techniques: ? EMWDÆ, Electro-Magnetic While Drilling ñ transmission of information between bottom hole and surface, and ? SWD, Seismic While Drilling - a survey technique using the drill bit as a seismic source, several multiradial surface geophones lines and a downhole reference sensor, placed in the Bottom Hole Assembly (BHA) including a shock absorber and a roller cone bit. The main objectives of this multidisciplinary approach, which should lead to the improvement of drilling techniques and a reduction of the mining risk and the direct costs of drilling operations, are: ? better control of directional wells during the kick-off phase, by real time transmission of drill-bit orientation parameters from bottom hole to surface; ? a detailed seismic image of the geological structure around the vertical well, useful for better definition of the drilling targets of the following directional wells; ? real time drill-bit localisation by means of a SWD integrated automatic monitoring system permanently installed at the well site. This should complement or avoid the conventional orientation measurements in the hot deep part of the wells. This paper relates the results obtained so far concerning the two first objectives, through a successful directional EMWD field test in the Larderello area, and a pre-operational EMSWD field test in a low temperature well using the new downhole recording BHA element built by GEOSERVICES, synchronised and interfaced with a commercial SERCEL SN388 surface seismic recorder. The new equipment behaved successfully on the field. The processing results are encouraging, thus allowing for the preparation of large-scale SWD operations on geothermal wells under drilling. |