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Comportement thermo-poro-mécanique d'un ciment pétrolier

Siavash Ghabezloo 1
1 cermes - Géotechnique
navier umr 8205 - Laboratoire Navier
Abstract : In oil wells, a cement sheath is placed between the rock and the casing for stability and sealing purpose. The cement lining is submitted to various thermal and mechanical loadings during the life of the well from the drilling phase to the production phase and finally in the abandon phase when the reservoir can be used for storage and sequestration of greenhouse gas. In due course of these solicitations, the cement can be damaged and the mechanical and transport properties can be degraded. This degradation can affect its contribution in the stability and in the sealing of the well. The knowledge of behaviour of this cement in oil-wells conditions (high temperature, high pressure) is essential for the prediction of the well performance during the exploitation and also for the analysis of the well tightness during storage and sequestration as the cement sheath is a possible leakage path.
In this thesis, an experimental study of the thermo-poro-mechanical behaviour of a hardened oil-well cement paste under high stresses and for temperatures between 20°C and 90°C is performed. The poro-mechanical behaviour of hardened cement paste under isotropic loading is studied on the basis of an experimental testing program of drained, undrained and unjacketed compression tests at 20°C and at 90°C. The poroelastic parameters of the material are determined and the effect of stress, pore pressure and temperature on them is evaluated. A phenomenon of degradation of elastic properties is observed in the test results. The microscopic observations showed that this degradation is caused by the microcracking of the material even under isotropic loading. The good compatibility and the consistency of the obtained poromechanical parameters demonstrate that the behaviour of the hardened cement paste can be described within the framework of the theory of porous media.
The poro-mechanical tests are combined with an evaluation of the evolution of permeability of the cement paste under loading using a transient method. Deviatoric loading tests have also been performed to study damage under deviatoric stress.
The effect of undrained heating on volume change and induced pore pressure increase is an important point to properly understand the behaviour and evaluate the integrity of an oil well cement sheath submitted to rapid temperature changes. This thermal pressurization of the pore fluid is due to the discrepancy between the thermal expansion coefficients of the pore fluid and of the solid matrix. A preliminary experimental and theoretical study has been performed on a granular rock. Careful analysis of the effect of mechanical and thermal deformation of the drainage and pressure measurement system has been performed and a simple method has been developed for the correction of the measured pore pressure. Then the effect of undrained heating is studied experimentally for a saturated hardened cement paste. The measured value of the thermal pressurization coefficient is equal to 0.6MPa/°C which shows that the changes in effective stress can be significant when the well is submitted to rapid temperature changes. The drained and undrained thermal expansion coefficients of the hardened cement paste are also measured in the heating tests. The anomalous thermal behaviour of cement pore fluid is back analysed from the results of an undrained heating test and is attributed to its confinement in very small pores.
In addition to this work on the behaviour of cement paste, an experimental study on the effective stress law for the permeability of a limestone is performed and a conceptual model is proposed in relation with the microstructure of the rock.
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https://pastel.archives-ouvertes.fr/tel-00403940
Contributor : Siavash Ghabezloo <>
Submitted on : Tuesday, July 14, 2009 - 5:38:07 PM
Last modification on : Monday, October 19, 2020 - 11:08:10 AM
Long-term archiving on: : Tuesday, June 15, 2010 - 8:01:21 PM

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  • HAL Id : tel-00403940, version 1

Citation

Siavash Ghabezloo. Comportement thermo-poro-mécanique d'un ciment pétrolier. Sciences de l'ingénieur [physics]. Ecole des Ponts ParisTech, 2008. Français. ⟨tel-00403940⟩

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