Drilling of Hot and Fractured Granite at Soultz-Sous-forets (France)

Abstract

The results of a drilling operation at Soultz sous Forits, France, are reported here which involved reaming and drilling of hot and fractured granites a low cost clear brine water mud. Highly permeable zones were temporarily sealed (to be available later for scientific investigations) by spotting pills of loss circulation material (LCM). Experience in Soultz indicated that the effectiveness of LCM pills under geothermal conditions at 3600m) can be increased considerably by giving the heat sufficient time to act on the mixture before resuming drilling. The well was completed with an uncemented 7" internal casing (0 - 2850 m) which is only supported at the bottom by an open hole casing packer and a short cementation. Thermal expansion and contraction, of the otherwise self-supporting pipes, (during injection and production experiments) are compensated in the well head assembly. Drilling operations (well cleaning, casing removal, reaming, drilling and completion) were finished after 60 days, some 20 days ahead of schedule.