Małgorzata Labus

Sandstone degradation: an experimental study of accelerated weathering

The investigated rock material belongs to the group of upper cretaceous quader sandstones which are very important construction stones in Poland and Germany. The mineral composition of the rocks is relatively uniform—they are quartzose sandstones. The most important feature is their good workability and comparatively high weathering resistance. Still, regardless of the apparent resemblance, the observations carried on buildings and monuments show differences in weathering processes. The undertaken test was an attempt to verify the proposed before rock classification, performed on the basis of parameterization of porosimetric cumulative intrusion volume curves. The aim of the experiment was the evaluation of the sandstone petrography (including the structure, texture and porosity of the rock) influence on the weathering process. The modelling of accelerated weathering was conducted in Chamber for Ageing Acceleration, where some weather circumstances were simulated (insolation, rain and frost). As the result of the weathering experiment it could be stated that the dominant mechanism of the sandstones deterioration was granular disintegration and weight loss as a consequence of sample destruction. The most important factor influencing rock deterioration is rock texture, especially the character of grain contacts. The effective porosity is a requisite of potential for the stone to take in and hold water, and hence of resistance to weathering. In case of silica-cemented sandstones, the deciding criterion influencing weathering resistance is pore structure. In case of sandstones with clay cement, the most important is mineral composition of the rock.

Thermal methods implementation in analysis of fine-grained rocks containing organic matter

The thermal methods, including TG and DSC techniques, were implemented to determine the composition of the fine-grained rocks with dispersed organic matter. The analyses were carried out in inert and oxidising atmosphere. The analysed samples represented Palaeozoic siltstones, shales, claystones and mudstones from Baltic Basin, Lublin Basin and Upper Silesian Coal Basin (Poland). There was detected the presence of some minerals as: clay minerals, muscovite, quartz, calcite, dolomite and pyrite. A comparison of the reactions occurring in an oxidising and inert atmosphere can give a solution to the problem of some effects overlapping, such as distinguishing pyrite decomposition from organic matter combustion. The analysis of DSC curves of heated rocks under oxidative atmosphere allows to determine the temperature regions of the organic matter combustion and to conclude on its maturity level. There was also found a strong correlation between the mass loss resulted from organic matter combustion, and the mass loss as a result of pyrolysis.

Identifying geochemical reactions on wellbore cement/caprock interface under sequestration conditions

Abstract The integrity of wells, which are key components for CO2 sequestration, depends mainly on the seal between the wellbore cement and the geologic formation. To identify the reaction products that may alter the cement/caprock interface, batch experiments and computer modelling were conducted and analysed. Over time, the dissolution and precipitation of minerals alters the physical properties of the interface, including its tightness. One main objective of the simulation was thus to analyse the evolution of the porosity of cement and caprock over time. The alteration of the cement/caprock interface was identified as a complex problem and differentiated depending on rock type. The characteristic feature of a cement/shale contact zone is the occurrence of a highly carbonated, compacted layer within the shale, which in turn causes cement/shale detachment. In the case of a cement/anhydrite interface, the most important reaction is severe anhydrite dissolution. Secondary calcite precipitation takes place in deeper parts of the rock. The cement/rock contact zone is prone to rapid mineral dissolution, which contributes to increased porosity and may alter the well integrity. Comparison of computer simulations with autoclave experiments enabled the adjustment of unknown parameters. This enhances the knowledge of these particular assemblages. Overall, a good match was obtained between experiments and simulations, which enhances confidence in using models to predict longer-term evolution.

Differential scanning calorimetry (DSC) in researching the mineral carbonation processes of cement materials, in terms of CO 2 sequestration

Mineral carbonation is one of the mitigation strategies considered for reducing atmospheric CO2 concentrations. The reuse of industrial solid wastes and residues (e.g. waste building material, including cement – which readily sequester CO2 at ambient temperatures and pressures) is often taken into consideration. The main barrier to the use of mineral carbonation is the rather slow reaction progress. Based on a literature review it has been hypothesized, that knowledge of the reaction energy of formation and disintegration of carbonate phases is needed, and differential scanning calorimetry (DSC) measurement method could be used to obtain thermodynamic data of the mineral carbonation process.