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Évolution au cours du temps des propriétés physiques et mécaniques des matériaux cimentaires d’un puit géothermique basse énergie

Abstract : In low energy geothermal wells (up to 2000 meters deep), cement is used in the annular space, between the casing and surrounding geological formations. Its role is to ensure the zonal isolation, the mechanical strength of the layers and the protection of the casing. The quality and stability over time of these cements are important. Given the geothermal gradient, water circulations loaded in chemical elements in the aquifer and strong confining stresses due to the depth, cement hydration is likely to be significantly influenced. Indeed, these factors may in the long term contribute to premature degradation of the well. The objective of this work is to examine the effects of environmental conditions of geothermal wells (temperature, pressure and concentrations of NaCl) on the physical and mechanical properties of cement pastes and microstructural inverstigations. Several grouts were sampled on a geothermal project in Ile de France. On this project, the class G cement grout and cement with bentonite grout are used throughout the well. Hardened cement pastes prepared in the laboratory were studied using a methodology based on non-destructive (ultrasonic wave velocity, resonance frequency, permeability) and destructive measurements (Young's modulus, compressive strength, thermal conductivity). Thermal and physico-mechanical properties of hardened cement pastes from these measures were coupled with microstructural observations by X-ray diffraction, scanning electron microscopy and mercury intrusion porosimetry. The results showed that the microstructural analyses concur with the physico-mechanical properties and are good indicators of the state of the cement in the well. This thesis proposes a reliable testing methodology. Indead, many tests and analyses provide relationships that predict the compressive strength of cement pastes a geothermal well. Finally, and irrespective of the environmental conditions applied, empirical relationships have been proposed. These link relations the results of non-destructive methods with those from destructive tests and can be used to determine the properties of cement pastes without carrying out destructive tests in geothermal wells
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Élodie Nauleau. Évolution au cours du temps des propriétés physiques et mécaniques des matériaux cimentaires d’un puit géothermique basse énergie. Autre. Université Paris-Est, 2013. Français. ⟨NNT : 2013PEST1132⟩. ⟨tel-00920098⟩

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