How to Upscale Geothermal Energy from Deep Fractured Basement in the Upper Rhine Graben? the Impact of a New 3D Seismic Data

Abstract

During 2018 summer, a large wide azimuth 3D seismic reflection of 180 km² was conducted by Électricité de Strasbourg over the Northern Alsace region (France). The main objective of this first 3D seismic acquisition for geothermal project in France was to image the nearly-vertical fracture network of the Upper Rhine Graben, to be able to design a multi doublet EGS geothermal project and to reduce drilling risk by optimizing the borehole trajectory by taking into account the geometry of the natural fracture/fault system. In order to achieve optimized well trajectories within the complex nearly vertical fractured area of Northern Alsace, a one year of data processing and interpretation was needed. This detailed investigation of 3D seismic data lead to a high resolution 3D cube of seismic data converted in depth. These data have benefited of a broadband acquisition and state of the art of seismic processing workflow. It results unrevealed geological faults probably making of Northern Alsace, the French most promising high temperature geothermal reservoir. Indeed, the development potential of Northern Alsace was confirmed by a recent hydraulic interference test between the Soultz-sous-Forêts wells and Rittershoffen geothermal sites far from seven kilometers showing however their hydraulic connection. This paper will describe the cost effective acquisition parameters selected to properly image the deep geothermal target corresponding to deep-seated fractured rocks, the processing workflow followed and the most relevant geophysical attributes produced to figure out high potential geothermal targets.