Seismic hazard related to deep geothermal operations (Part II) : iterative methodology for hazard assessment

Ineris and BRGM published a good practices guide and recommendations for the management of seismicity induced by deep geothermal energy operations. It includes a method to assess the seismic incident hazard, defined as an event whose intensity could cause nuisances for the population, affect the local buildings and infrastructures and which could adversely impact the operating conditions and even the continuation of the project. This method has been developed based on more than 50 case studies consisting of projects representative of different types of geothermal systems where induced seismicity occurred or not. Based on an iterative approach, the method recommends hazard assessment at each key step of a geothermal project to benefit from the additional knowledge it bring. The main key steps identified are the initial assessment before frilling occur, a reevaluation just after drilling and a reevaluation before any potential stimulations. Hazard assessment is based on a decision tree approach, involving specific criteria for each project phase. The seismic incident hazard is rated with a score between 0 and 3. At the lowest level (0), no specific measures to manage induced seismicity are required. For level 1 and 2, monitoring and management methods must be developed. At level 3, the project is considered to be beyond potential induced seismicity management (it’s deviating from the plan) and operations must be suspended pending the outcome of further investigations. This method has been tailored for helping and guiding operators and French administration to consider and manage induced seismicity hazard for every deep geothermal project.