DC7-PhD: Dynamic fracturing in a THM framework: Upscaling applications to geo-energy production and induced seismicity

22 de May de 2023

This research project aims to improve the control over induced seismicity events during deep geothermal energy exploitation by enhancing our understanding of pressure and temperature diffusivity, and their interactions with existing stress fields in fractured rock. To achieve this, robust fully coupled thermo-hydro-mechanical models will be developed that include dynamic fracturing processes. By applying the model to various project configurations and using statistical analysis, we can identify the combinations of processes that result in severe induced seismicity.

Objectives: This work includes the development of a fully coupled THM framework based on pre-existing finite element codes. A dynamic fracturing model, which accounts for released kinetic energy, is to be integrated in the THM framework. Once the dynamic THM fracturing platform is developed, it will be applied to different project configurations. Given the inherent uncertainties in the knowledge of geothermal systems, a statistical analysis will be carried out to estimate the impact of the variation of model input parameters on the risk of rupture and fault reactivation and thus, optimize the production while reducing the risk of felt seismic events. Induced seismicity will be utilized in an inverse analysis approach to plot the hydraulic fracture envelope. It will be also used in calculating the kinetic energy spread in the medium, and henceforth controlling/predicting the magnitude of induced seismic eventsĀ 

Expected Results: We would aspire to develop an upscaling approach where our THM dynamic fracturing platform can be applied to large geological scales while taking into account natural anisotropies. Such anisotropies self-demonstrate in terms of elastic, dynamic, and transport properties. Once this upscaling approach is developed, we will consider models with large faults that can be assigned different dynamic and fluid transport properties from the surrounding rock formation. We expect that assigning to faults weaker elastic and dynamic properties would affect the directional homogeneity of far-field geological stresses, which would consequently, have direct impacts on the shape and orientation of the created fluid driven fractures. The fluid-heat interaction with geological faults and pre-existing natural defects/joints is expected to trigger slip and to induce seismicity. Inverse analysis techniques will be utilized to locate seismic events, specifically during shut-in and flow back to better understand and evaluate post-peak induced seismicity. We will also investigate the influence of different injection scenarios/multi-stage fracturing, fault orientation with respect to the injection well, and the amount of the injected fluid on the efficiency of the reservoir development prior to further exploitation.

Doctoral candidate: Khashayar Khezri

Host Institution: Armines (France)

Secondments: ETHZ, CSIC, CTTC