EGS Probabilistic Seismic Hazard Assessment with 3-D Discrete Fracture Modeling

Authors: Dimitrios KARVOUNIS, Gischig, VALENTIN, Stefan WIEMER
Keywords: probabilistic seismic hazard assessment, EGS, induced seismicity, modeling
Conference: Stanford Geothermal Workshop Session: Enhanced Geothermal Systems
Year: 2014 Language: English
Abstract: Hydraulic fracturing is essential for many deep reservoir engineering projects which rely on permeability enhancement due to injections of fluid that has high pressure. The stimulation of such reservoirs induces felt seismicity which causes public anxiety and in some occasions may be a potential hazard for the local population and structures. The progress of novel technologies, such as Enhanced Geothermal Systems (EGS), has decelerated due to this induced seismicity. Hazard and risk assessment tools, such as sophisticated traffic light systems, which operate during the well stimulation, can assist in the safe development of EGS sites located close to urban areas. We present here the modeling approach for such a near-real time traffic light system that is currently under development. This system uses a hybrid model that solves the mass conservation equations for a reservoir model that has a dynamically changing fracture network, similar to an EGS, and applies stochastic models for the creation of synthetic catalogs. It is based on HFR-Sim, which is an EGS simulator that uses an adaptive hierarchical discrete model and models flow and heat transport in EGS reservoirs. This EGS simulator provides the necessary input to the stochastic models employed for the induced seismicity. The newly triggered seismic events are included in the flow model as an enhancement to the permeability of the existing ones and, thereafter, are treated as discrete fractures. The presented model is expected to use real time data for calibration and will consecutively create catalogs that include seismic events, magnitudes and well logs. These can be used afterwards for performing probabilistic induced seismicity hazard assessment (PISHA) of the planned stimulation strategy. This way, the well operators will be assisted in their decision making. Additionally, HFR-Sim can perform simulations of the production phase inside the network of fractures that is obtained once each induced seismicity simulation is over. Here, it is explained how this traffic light system with the 3D discrete fracture modeling is expected to work and demonstrative behavior is presented in artificial scenarios. The model is used for simulating an artificial scenario which includes the stimulation of two wells and the production phase of the EGS reservoir afterwards.
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