The geothermal research well GtGrSk4/05 at Gross Schonebeck, Germany, was hydraulically stimulated to develop an Enhanced Geothermal System in the Upper Rotliegend sandstones. Gel-proppant stimulation was selected to enhance reservoir productivity and to maintain it over the long term. Before the field tests, laboratory experiments were carried out to study embedding effects and long-term hydraulic conductivity changes in intermediate- and high-strength proppant types. Based on the laboratory results it was decided to place in the stimulated fractures large concentrations of a high-strength proppant. The success of the stimulation of GtGrSk4/05 was confirmed by production test and flowmeter log data. (c) 2010 Elsevier Ltd. All rights reserved.