Current State of the EGS Project Gro? Sch?nebeck - Drilling into the Deep Sedimentary Geothermal Reservoir

Abstract

In the context of the Geothermal Technology Program at GFZ, the former gas exploration well Gro? Sch?nebeck 3/90 (50 km northeast of Berlin) was reopened and deepened to 4309 m depth. For the last 6 years, this well has served as a geothermal in-situ laboratory for in situ experiments and the development of stimulation concepts. The objective of these stimulation operations was to create secondary flow paths and to improve the inflow performance of the well. The well makes the deep sedimentary Rotliegend reservoir accessible, which is characterized by water bearing porous and fractured rocks. To complete a potential doublet for power generation, the second well Gro? Sch?nebeck 4/05 was drilled in late 2006. At pay-zone depth level the maximum distance between the two wells is approximately 500m. The most promising sandstone layers for stimulation were identified by measured porosity distribution, water saturation and calculated permeability data. This information is a prerequisite for the decision on perforation depths. Further experiments are forseen in 2007 now using both wells. This article describes the challenges and experiences of drilling the geothermal research well into a deep sedimentary geothermal reservoir. The lessons learnt covers drilling large diameter in sheet silicate bearing rocks, directional drilling through and beneath salty formations, and various mud concepts with the goal of minimized formation damage.