Re´sume´-É volution des proprie´te´s e´lastiques d'une paˆte de ciment pe´trolier au tre`s jeune aˆge dans des conditions HP/HT : caracte´risation expe´rimentale et mode´lisation -Une mode´lisation multie´chelle, couple´e avec un mode`le d'hydratation, est propose´e pour pre´dire l'e´volution des proprie´te´s e´lastiques d'une paˆte de ciment pe´trolier au tre`s jeune aˆge (jusqu'a`un jour). Des re´sultats expe´rimentaux montrent que la pression applique´e (1-200 bar) pendant la prise a peu d'effet sur la cine´tique d'hydratation contrairement a`la tempe´rature (20-60°C). Le mode`le d'hydratation retenu a e´te´valide´par des mesures calorime´triques. Les re´sultats de porosited e´duits de ce mode`le d'hydratation sont d'ailleurs cohe´rents avec des mesures de la porositeć onnecte´e effectue´es a`diffe´rents degre´s d'hydratation. La mode´lisation multi-e´chelle par homoge´ne´isation prend en compte l'e´volution des fractions volumiques des constituants de la paˆte de ciment au cours de l'hydratation. Le de´veloppement des proprie´te´s e´lastiques du ciment pe´trolier au tre`s jeune aˆge obtenues avec ce mode`le est en bon accord avec les mesures obtenues par la propagation d'ultrasons.Abstract -Evolution of the Elastic Properties of an Oilwell Cement Paste at Very Early Age under Downhole Conditions: Characterization and Modelling -A multi-scale homogenization approach coupled with a hydration model is adopted to predict the bulk and shear moduli evolution of an oilwell cement paste at a very early age (up to one day). Calorimetric experiments were performed to be compared with the results of the kinetics model and also to study the pressure and temperature effects on the hydration kinetics. The homogenization model results are in agreement with the elastic moduli measurements obtained from propagation of ultrasonic waves.

The characterisation and modelling of the mechanical behaviour of an oilwell cement paste at a very early age (≤24h) under high pressure and elevated temperature are studied. A multiscale homogenization approach is adopted. For this purpose, the evolution of the volume fractions of the different phases of the cement was determined by means of a kinetics model for the four main hydration reactions of a class G oilwell cement. Calorimetric experiments were performed in order to be compared with the results of the used kinetics model, on the one hand, and to study pressure and temperature effect on the hydration kinetics, on the other hand. A homogenization model is presented in order to predict the bulk and shear moduli evolutions. The model-based results are in agreement with dynamic moduli measurements data from ultrasonic propagation.