PhD opportunities

Numerical Modeling of Delayed Seismicity in Enhanced Geothermal System

Thesis proposal

Area of expertiseGosciences et goingnierie
Doctoral SchoolGRNE - Gosciences, Ressources Naturelles et Environnement
SupervisorM. Frdric PELLET
Research unitGeosciences
ContactPELLET Frdric
KeywordsGeomechanics, Numerical Modeling, Statistics
AbstractThis project intends to develop a comprehensive numerical simulator for the modeling of the entire exploitation process taking place at depth. This Geo-Engineering simulator will include the following three modules:
 Thermo-Hydro-Mechanical of the dynamic process of rock fracturing in a natural pre-fractured environment
A well known limiting factor is the potentially low hydraulic permeability of the naturally fractured formations that can result into inappropriate pressure changes. In this context, the Thermo-Hydro-Mechanical dynamics modeling (THM) aims to reproduce the changes in terms of mechanical stress and strain, associated with the change in pore pressure regime and temperature, due to the operation of water production-injection. Actually, the high pressure fluids injected into tight reservoirs are expected to initiate or propagate fractures and activate critically stressed faults, which emit energy in the form of micro-seismic events. The modeling of this phenomenon will be treated using the eXtended Finite Element Method (XFEM) which is a numerical technique, relying on Linear Elastic Fracture Mechanics theory (LEFM). LEFM allows the modeling of crack initiation and propagation due to the change in pore pressure resulting from hydraulic stimulation, in any given far field stress context. THM modeling will be performed in dynamics formulation with appropriate algorithms, because the brittle failure of hard rock is a dynamic process.
 Inverse analysis and modeling of seismic waves propagation
The dynamic brittle failure of rock also generates seismic waves which can be experimentally measured at a lab scale, on rock specimen using Acoustic Emissions technique. On the field these waves propagation give a seismic signal which is characterized by the Peak Ground Acceleration. Based on the seismic measurements, it is possible to locate the crack initiation and to assess the crack extension using inverse analysis algorithms. In the present work, it is proposed to extend this approach by analyzing the seismic records to determine, not only some characteristics of the fracture network geometry, but also the hydro-mechanical properties of the geothermal reservoir. Moreover, this will allow one to calibrate the constitutive parameters of the THM model described above.
 Stochastic geomechanical modeling
The last part of this research project is devoted to the appraisal of uncertainties through stochastic geomechanical modeling. The latter encompasses the knowledge of the initial stress regime, as well as information on the location and the extension of pre-existing fracture networks. Because all these data are quite uncertain, advanced stochastic modelling is required to determine the most likely scenarios to better constraint the geomechanical model
FundingAutre type de financement