Application of the geomechanical facies approach and comparison of exploration and evaluation methods used at Soultz-sous-Forêts (France) and Spa Urach (Germany) geothermal sites

Abstract

Earth-reservoirs are increasingly exploited today with the extraction of resources, such as heat and hydrocarbons, and the large-scale emplacement of waste, such as CO 2 sequestration. The characterization, site investigation, predictive modeling and long-term monitoring are dependent on the processes being investigated and modeled. In most cases complex coupled processes have to be addressed in a geologically complex rock mass system. In this paper we present a conceptual holistic framework known as geomechanical facies linking all the scales of investigation, characterization and reservoir development methods. We demonstrate this concept on the work undertaken during the design and development of the enhanced geothermal systems (EGS) systems at the forefront of European HotDry-Rock (HDR) technology, Soultz-sous-Forêts (France) and Spa Urach (Germany). Soultz-sous-Forêts is situated within granitic rocks and an active tectonic graben system in the central part of the Rhine Graben. It presents conditions of lithology, temperature, stress, hydraulics and geochemistry that are very different from those at Spa Urach, located in a very dense gneiss formation in the South German crystalline complex. Spa Urach exhibits more elastic behavior and is set tectonically within an almost inactive strike-slip stress field described in more detail in Sects. ''Drill core analysis'' and ''Hydraulic stimulation at Spa Urach''. This paper compares the exploration and field development methods used at these two sites against the back drop of the geomechanical facies concept. Issues addressed include the key parameters for flow and heat transport properties, coupled hydro-mechanical process identification, the success of the HDR reservoir as a heat exchanger and exploration techniques applicable to the different facies. Identification of the key geomechanical facies gives an indication as to which technologies will prove more efficient in the application of HDR technology. The results of this study will hopefully help in developing heat recovery schemes for the long-term economical operation of future HDR plants and EGS as well as assist in the understanding of engineered geosystems.

GEM-Selektor geochemical modeling package: revised algorithm and GEMS3K numerical kernel for coupled simulation codes

“…Applications are in the fields of groundwater and surface hydrology, water resources, geotechnics, radioactive waste disposal, geothermal energy, and CO 2 storage [7,30,35,46,47,51,54,60,63]. The concept of OpenGeoSys is a distributed open source scientific software development that should benefit from joint efforts of all involved groups.…”

Geoenergy Modeling I

“…Urach Spa was one of the most important scientific geothermal pilot projects in Germany even though it failed but it provided deep insight into the complexity of deep geothermal systems (Tenzer et al 2010). Watanabe et al (2010) developed a numerical THM model for the Urach Spa location.…”

A study on the interaction of mud acid with rock for chemical stimulation in an enhanced geothermal system

“…The trial of chemical stimulation in the EGS field succeeded in the Soultz-sous-Forêts (Tenzer et al 2010), which is one of the most famous EGS sites consisting of three boreholes and started to generate electricity in 2008. An intensive research has been performed in order to assess the permeability of the flow pathways in the reservoir and insure the connectivity between these three wells (Hébert et al 2010;Ledésert et al 2010;Gentier et al 2010;Sanjuan et al 2006).…”