Autogenous Shrinkage of Hardening Cement Paste in Oil Wells: Fid-Bau Portal

Autogenous Shrinkage of Hardening Cement Paste in Oil Wells

Blanc, A. / Faure, P. / Le Roy-Delage, S. / Fen-Chong, T.

In cementing technology for oil and gas wells, the autogenous deformations driven by the hydration of a cement annulus are not well understood and predicted. Cement hydration in deep wells governs the state of stress in the cement annulus after its placement and thus, the safe operational margins in well pressure and temperature. Early-age cement autogenous deformations thus play a critical role in the life of the well. Our objective is to provide an experimental study of these deformations as a function of temperature, pressure and the access to water during hydration to improve theoretical predictions. We assume that the origin of the deformation is due to the partial desaturation of the pores which then causes a variation in capillary pressure that induces bulk shrinkage of the early-age cement. The mechanical properties are described using the standard Zener viscoelastic model, where aging is incorporated by the degree of hydration. We investigate the hydration reaction through NMR relaxometry and combine the results with calorimetric data to provide a critical analysis of the hydration model proposed by Lin and Meyer. By doing so, the latter is found to neglect the duration of the induction period and underestimate the early hydration degree, particularly at low temperature. We finally show that this underestimation of the early hydration leads to a significant over-estimation of the prediction of the autogenous shrinkage in a hardening cement by a poro-viscoelastic model, compared to experimental results.