Evaluation of THC stimulations from acoustic image logs in the geothermal Rittershoffen well GRT-1 (France)

Abstract

In the Upper Rhine Graben (URG), several deep geothermal projects exploit local geothermal energy trapped in the fracture network of Triassic sediments and the granitic basement below (Soultz-sous-Forêts, Landau, Insheim...). Those projects are based on the Enhanced Geothermal System (EGS) technology. The principle of the EGS technology consists in increasing the low natural hydraulic performance of the geothermal reservoir by hydraulic or/and chemical stimulations. These stimulations increase the natural permeability to commercial level. The ECOGI project located in Rittershoffen (Alsace, France) is an industrial project that targets the geothermal resource at the sediment-basement interface to produce geothermal heat (Baujard et al., 2014). The first geothermal vertical well GRT-1, drilled to 2.6 km deep in 2012, didn’t have a sufficient injectivity for the future industrial exploitation and has been thermally, chemically and hydraulically (THC) stimulated in 2013. The open-hole section is composed by fractured Triassic sandstones and Paleozoic altered granite and two-mica granite. The target of the study is an evaluation of the stimulation effect based on analysis and comparison of various borehole data including dynamic data and acoustic borehole images logs collected before and after stimulation.