Influence de la température sur l'activité micro-sismique dans un réservoir fracturé lors d'injections de longue durée. Application aux données du site de Rosemanowes (UK). Première approche d'un site potentiel dans le rift d'Assal (Djibouti)

Abstract : The general framework of our research deals with the development of geothermal energy for electricity production using the heat stored in geological formations at depths ranging in 3 to 5 km, Generally the environment is poorly permeable and fractured. Our main objective is to study the phenomenon of induced micro-earthquakes in relation to the cooling of the rock. The work is based on field experiences including long duration tests, conducted on the Rosemanowes site (Cornwall, UK). For this, we proceeded to the development of a calculation tool, FRACAS, able to simulate this phenomenon by introducing a dual thermal approach to better simulate the cooling of the reservoir due to long term fluid injections, which might be responsible for new failure mechanisms due to the induced tractions. In this context, we introduced a new algorithm to describe shear in stabilities, a mechanism of "stick-slip" type with the consideration of static/dynamic friction coefficients. The possibility of inducing micro-seismicity is then studied using the in situ data base, with two 3D models offering different geometric approaches, a deterministic model and a stochastic model whose geometrical and physical properties were obtained from observations and previous work on this Rosemanowes site. The Thermo-Hydro-Mechanical (THM) simulation using the deterministic model has allowed us to calibrate the transient heat transfer in the reservoir formed by the drilling system RH12/RH15 and to give an estimate of tensile stress of thermal origin. To better study the effect induced by the contraction of the rock during time, we use the stochastic 3D model whose main objective is to simulate a more realistic spatial migration of shear ruptures. With this model we found a delayed onset of shear activity and discuss the effect of pressure step tests. The results suggest a way to mitigate the potential impact of shear ruptures due to cooling.
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Ahmed Kayad Moussa. Influence de la température sur l'activité micro-sismique dans un réservoir fracturé lors d'injections de longue durée. Application aux données du site de Rosemanowes (UK). Première approche d'un site potentiel dans le rift d'Assal (Djibouti). Sciences de la Terre. Ecole Nationale Supérieure des Mines de Paris, 2013. Français. ⟨NNT : 2013ENMP0084⟩. ⟨tel-01310481⟩

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