Designed 3D Seismic Imaging to Better Understand Geothermal Faulted Reservoir, an Upper Rhine Graden Case History

Abstract

Over the past 35 years, geothermal projects have been developed in Upper Rhine Graben (URG) to exploit deep geothermal energy. Below couple kilometers of sediment, deep target consist of granitic basement, highly fractured and hydrothermally altered, having a high reservoir potential. Despite dense 2D seismic coverage, the faults at the top of the granitic basement are poorly imaged and their locations remain uncertain. In order to better understand large scale faulting and ensure viability of future geothermal projects, 3D seismic survey has been shot in the French part of the URG during summer 2018. To maximize the wave penetration and the good imaging of deep faulting, low frequency source sweep was used (2Hz – 96Hz) with a regular carpet shooting leading to a natural bin size of 20m by 40m. This paper will present how most recent seismic imaging sequence was designed in order first to process the acquired data and then to build a depth velocity model allowing accurate positioning of the faulting. Along processing, wells control and reservoir information were incorporated to guarantee proper well tie of the final image and reliable AVO attributes. These attributes will then be used for further quantitative reservoir analyses such as fracture and permeability, critical for geothermal system development.