29 research outputs found
The effect of undrained heating on a fluid-saturated hardened cement paste
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. The equations governing the undrained
thermo-hydro-mechanical response of a porous material are presented and 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. 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 the undrained heating test.Comment: Cement and Concrete Research (2008) In pres
Evaluation of a permeability-porosity relationship in a low permeability creeping material using a single transient test
A method is presented for the evaluation of the permeability-porosity
relationship in a low-permeability porous material using the results of a
single transient test. This method accounts for both elastic and non-elastic
deformations of the sample during the test and is applied to a hardened class G
oil well cement paste. An initial hydrostatic undrained loading is applied to
the sample. The generated excess pore pressure is then released at one end of
the sample while monitoring the pore pressure at the other end and the radial
strain in the middle of the sample during the dissipation of the pore pressure.
These measurements are back analysed to evaluate the permeability and its
evolution with porosity change. The effect of creep of the sample during the
test on the measured pore pressure and volume change is taken into account in
the analysis. This approach permits to calibrate a power law
permeability-porosity relationship for the tested hardened cement paste. The
porosity sensitivity exponent of the power-law is evaluated equal to 11 and is
shown to be mostly independent of the stress level and of the creep strains
Poromechanical behaviour of hardened cement paste under isotropic loading
The poromechanical 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. The macroscopic behaviour of the
material is described in the framework of the mechanics of porous media. The
poroelastic parameters of the material are determined and the effect of stress
and pore pressure on them is evaluated. Appropriate effective stress laws which
control the evolution of total volume, pore volume, solid volume, porosity and
drained bulk modulus are discussed. 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 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 indeed described within the framework of the theory of porous
media.Comment: Cement and Concrete Research (2008) In pres
Armouring of well cement in H2S-CO2 saturated brine by calcite coating -- experiments and numerical modelling
International audienceThe active acid gas (H2S-CO2 mixture) injection operations in Nortn America provide practical experience for the operators in charge of industrial scale CO2 geological storage sites. Potential leakage via wells and their environmenal impacts make well construction durability an issue for efficiency/safety of gas geological storage. In such operations, the well cement is in contact with reservoir brines and the injected gas, meaning that gas-water-solid chemical reactions may change the physical properties of the cement ans its ability to confine the gas downhole. The cement-forming Calicum silicate hydrates carbonation (by CO2) and feriite sulfidation (by H2S) reactions are expected. The main objective of this study is to determine their consequences on cement mineralogy and trasfert ability. 15 and 60 days duration batch experiments were performed, as welle as numerical simulation of the experiments. The work suggest that in both acid gas and CO2 geological storage, clogging of cement or at least mineral assemblage conservation and slowing of carbonation progress could occur in near-well zones where slight water flow occurs e.g. in the vicinity of caprock shales
Well cement ageing in various H2S-CO2 fluids at high pressure and high temperature: experiments and modeling
International audienc
High prevalence of cognitive impairment after intracerebral hemorrhage.
BACKGROUND:Cognitive impairment seems to be frequent in intracerebral hemorrhage (ICH) survivors, but remains widely understudied. In this study, we investigated the frequency and patterns of vascular cognitive disorders (VCDs) in patients with cerebral amyloid angiopathy (CAA)-related and deep ICH compared to patients with mild cognitive impairment due to Alzheimer's disease (MCI-AD) and healthy controls. METHODS:We prospectively recruited 20 patients with CAA-related lobar ICH, 20 with deep ICH, 20 with MCI-AD and 17 healthy controls. Patients with cognitive decline pre-ICH were excluded from the analysis. Each participant underwent a comprehensive neuropsychological assessment and a structural brain MRI. Cognitive assessment was performed at a median delay of 4 months after the acute phase in ICH patients, and more than 6 months after the first complaint in MCI-AD patients. Cognitive profiles were compared between groups. The prevalence of VCDs in the ICH groups was estimated using the recent VASCOG criteria. RESULTS:"Mild" and "major VCDs" were respectively observed in 87.5% and 2.5% of all ICH patients. Every patient in the CAA group had mild VCDs. No significant difference was observed in cognitive functioning between CAA-related and deep ICH patients. The most impaired process in the CAA group was naming, with a mean (±standard deviation) z-score of -5.2 ±5.5, followed by processing speed (-4.1±3.3), executive functioning (-2.6 ±2.5), memory (-2.4 ±3.5) and attention (-0.9 ±1.3). This cognitive pattern was different from the MCI-AD patients, but the groups were only different in gestural praxis, and by construction, in memory processes. CONCLUSIONS:VCDs are frequent after ICH. Cognitive patterns of patients with deep or CAA-related ICH did not differ, but there was impaired performance in specific domains distinct from the effects of Alzheimer's disease. CLINICAL TRIAL REGISTRATION:URL: http://www.clinicaltrials.gov. Unique identifier: NCT01619709