Étude et modélisation de l'alteration physico-chimique de matériaux de cimentation des puits pétroliers

Cement-based materials are used for a long time in oil and gas industry for cementing oil wells. The main role of the cement sheath is to permanently isolate all subsurface formations penetrated by the well. With the growing interest for the environmental concerns (limitation of hydrocarbon pollutants releases, CO2 geological storage), the long-term durability of the cement-based materials used for well construction has become of paramount importance. The principal aim of this present work is to better understand oil-wells cement behaviour during leaching under downhole conditions, and predict its long-term durability. An experimental setup allowed degradation of cement exposed to specific brine with a perfect control of different parameters (temperature, pressure, flowrate, composition). Three leaching tests were performed on cement pastes. The temperature and pressure conditions were as following: 80 °C – 1 bar, 80 °C – 70 bars and 80 °C – 200 bars. The results reported structural and chemical differences between the cement pastes observed after the two types of curing, leading to a different behaviour after leaching test. Moreover, the kinetics of degradation increases at highest pressures because of different solubility of minerals. Simulations were made with the reactive transport model HYTEC and reproduced the main experimental results obtained after cement paste leaching. Consequently, this present work allows news perspectives for researches on oilwell cement behaviour under elevated geological conditions.Les matériaux cimentaires sont utilisés dans l'industrie pétrolière pour la construction des puits. Le rôle principal de cette gaine de ciment est d'isoler entre elles les formations géologiques traversées par un puits pétrolier et ce, de manière permanente et pérenne. De nouveaux enjeux environnementaux pour l'industrie pétrolière (limitation des rejets de polluants hydrocarbonés, stockage géologique du CO2) impliquent une meilleure compréhension de la durabilité à long terme des matériaux utilisés pour la cimentation des puits pétroliers. Cette thèse a pour objectif principal de mieux comprendre le comportement de matériaux cimentaires soumis à la lixiviation en conditions de fond de puits et de prédire leur durabilité à long terme. Un montage expérimental a été mis au point permettant de simuler la dégradation de matériaux en température et pression, avec un renouvellement permanent du fluide agressif. Les tests de dégradation ont été effectués à 80°C-1 bar, 80°C-70 bars et 80°C-200 bars. Il a été montré lors de ces travaux que le mode de maturation de la pâte de ciment, correspondant à différentes localisations du matériau au sein d'un puits, influençait la cinétique de dégradation de la pâte de ciment durant sa lixiviation. De plus, la cinétique de dégradation des pâtes de ciments est plus élevée aux hautes pressions à cause, notamment, de différences de solubilité des minéraux. Les simulations effectuées à l'aide du code de transport réactif HYTEC ont permis de reproduire les principaux résultats expérimentaux. Cette thèse ouvre par conséquent de nouvelles perspectives de recherches sur la dégradation des matériaux cimentaires en conditions géologiques sévères

Innovative Leaching Tests of an Oilwell Cement Paste for CO2 Storage: Effect of the Pressure at 80°C

AbstractOld wells could be exposed to severe environment. This study reports the characterization of a class G oilwell cement paste exposed to a brine at high pressure and high temperature.The results showed that pressure had a strong impact on the phenomenology and the kinetics of oilwell cement paste degradation in selected downhole conditions. The alteration mechanism at high pressure appears to be more complex than the one observed at atmospheric pressure. At atmospheric pressure the diffusion rate governs the kinetics and thus is slower than the rate of the chemical reaction. On the other hand, it seems that an increase of pressure increases much more the diffusion rate than the rate of reaction. Future developments are proposed in order to improve the understanding of the long-term behavior of oilwell cement paste at downhole conditions

Geochemical variations in early Islamic glass finds from Bukhara (Uzbekistan)

International audienceGlass manufacturing processes and recipes changed fundamentally after the 8th century CE. The earlier centralised production system diversified, primary production sites multiplied, and the scale of individual productions contracted. Mineral soda was no longer used and instead replaced by plant ash as the main fluxing agent, affecting the chemical composition and properties of the glass. In this work, LA-ICP-MS and Raman spectroscopy were used to investigate the compositional and structural characteristics of 68 glass fragments recovered during recent excavations at Bukhara in Uzbekistan, dating to the 9th to early 11th centuries CE. This is the most extensive systematically collected and studied glass assemblage from Central Asia to date. The glass can be attributed to different origins, confirming on the one hand the diversification of glass production during the early Islamic period and, on the other hand, regional variations in the chemical compositions and network structure of soda-rich plant ash glasses. As clear archaeological evidence for early Islamic glass production sites in Central Asia is rare, regional production groups are distinguished primarily on relative concentrations of Mg, K, P, Cl, Li and Cs in relation to the plant ash component, while variabilities in Al, Ti, Cr, Y, Zr, Th and REEs and their ratios indicate different silica sources. Raman spectra suggest variations in network connectivity and Qn speciation that confirm compositional groupings and suggest structural differences between regional productions of plant ash glass. The results demonstrate a clear dominance of local or regional glass groups, while revealing the importation of Mesopotamian glass, notably a high-end colourless glass type from the region around Samarra in Iraq. The new analytical data allow further separation and characterisation of novel early Islamic plant-ash glass types and their production areas

A highly virulent variant of HIV-1 circulating in the Netherlands

We discovered a highly virulent variant of subtype-B HIV-1 in the Netherlands. One hundred nine individuals with this variant had a 0.54 to 0.74 log10 increase (i.e., a ~3.5-fold to 5.5-fold increase) in viral load compared with, and exhibited CD4 cell decline twice as fast as, 6604 individuals with other subtype-B strains. Without treatment, advanced HIV-CD4 cell counts below 350 cells per cubic millimeter, with long-term clinical consequences-is expected to be reached, on average, 9 months after diagnosis for individuals in their thirties with this variant. Age, sex, suspected mode of transmission, and place of birth for the aforementioned 109 individuals were typical for HIV-positive people in the Netherlands, which suggests that the increased virulence is attributable to the viral strain. Genetic sequence analysis suggests that this variant arose in the 1990s from de novo mutation, not recombination, with increased transmissibility and an unfamiliar molecular mechanism of virulence