GPK-2 re-entry and deepening -- a technical report

Abstract

Between mid February to end of May 1999 (in 104 days) the well GPK2 at the Soultz HDR site was successfully re-entered and deepened from 3876 m to a final depth of 5084 m and fully completed. Re-entry included the pulling of the existing 321 1 m long internal 9 5/8-inch by 7-inch casing string, fishing of a submersible pump and some 150 m of 2 3/8-inch tubing, sealing of a major loss zone and opening of a 6 1/4-inch well section in granite (3211-3876 m) to 8 1/2-inch hole size. The well was extended to 5048 m in 8 1/2'' hole size and again completed with a floating 9 5/8-inch by 7-inch casing string. The casing shoe is at 4431 m. A bottom hole core was taken in the depth range 5048-5051 m. The core recovery was app. 40%. A pilot hole in 6 1/4-inch was drilled from 5051-5084 m for in situ stress measurements using the hydraulic fracturing technique. The re-entry and deepening of the well GPK2 was accompanied by several technical developments. New casing packer elements based on inflatable metal shells were developed in a close cooperation between SOCOMINE and MeSy GmbH (patent pending). These packer elements were successfully integrated into the completion of the well. The full weight of the casing string is supported by these elements which are filled with and imbedded in cement. High temperature cementing strategies (up to 170-190 C) for the complex saline fluids encountered in Soultz (High Magnesium Resistant Cements) were developed in a cooperation between Schlumberger Dowell (Vechta), SOCOMINE, SII of Houston, Ruhr-University Bochum, BGR Hannover and IFP Paris. The development of several high temperature logging tools (200 C range, 6-arm caliper, PTF probe) was initiated with CSMA (Cornwall) during the preparation of the deepening of GPK2. Initial scientific investigations included borehole logging (NGS, CLIPER, ARI, UBI, TEMPERATURE), geological investigations (cuttings, core) and seismic monitoring while drilling. During the first temperature log performed, 12 hours after circulation, a temperature of 194 C was recorded at 5048 m (bottom hole at that time) when the temperature tool failed. At this time the temperature was still climbing. Geological investigations and borehole logging indicate a strong degree of fracturation in the open hole section between 4431-5084 m. Several zones of hydrothermal alteration were identified