Thomas Kempka

Physical Properties of Sandstones After High Temperature Treatment

Under the influence of high temperatures below the rock melting point, rock micro-structures change significantly (Dwivedi et al. 2008), new micro-cracks are developed, and pre-existing ones extended/widened (Den’gina et al. 1994). Meanwhile, various physical and mineralogical changes take place in the rock matrix. After cooling down to room temperature, thermal-induced changes are irreversible to some extent. Hence, rock physical properties from a macroscopic point of view are temperature-history dependent as they rely on the maximum temperature experienced. Knowledge on this issue is a key factor for successful implementation of modern geotechnical engineering projects, such as nuclear waste storage (Sundberg et al. 2009), underground coal gasification (Roddy and Younger 2010), geological CO2 storage (Rutqvist et al. 2002), geothermal heat extraction (Zhao 2000) and stability analysis of constructions in rocks after exposure to fire (Zhan and Cai 2007). Sandstone is a common sedimentary rock, having broad applications in geotechnical engineering. Therefore, the research on the thermo-physical properties of sandstones is extremely meaningful on a wide range. In this manuscript, an extensive review of international literature, especially of Chinese publications not considered in the English-speaking scientific community so far, covers physical properties such as bulk density, porosity, permeability and compressional wave velocity of sandstones after high temperature treatment. The considered sandstones along with their characteristics are listed in Table 1. The testing procedures of thermal treatment in the references reviewed in this manuscript are identical, taking into account heating the samples at a certain rate and under atmospheric pressure conditions in a furnace until a predetermined temperature is reached. The maximum temperature is maintained for a period (several hours), and then cooled down in the furnace or at ambient conditions. The detailed testing parameters for each reference reviewed are summarized in Table 2.

Mechanical Properties of Sandstones Exposed to High Temperature

Modern rock engineering applications such as deep geological disposal of nuclear waste (Ringwood 1985; Gibb 1999; Hokmark and Claesson 2005; Gibb et al. 2008; Sanchez et al. 2012), geothermal heat (especially of hot dry rock) extraction (Zhao 2000; Ghassemi and Zhou 2011; Feng et al. 2012; Gelet et al. 2012; Cherubini et al. 2013), and underground coal gasification (Burton et al. 2007; Luo et al. 2011; Kempka et al. 2011; Younger 2011; Nakaten et al. 2014) experience high-temperature environments, where rocks generally experience high temperatures up to several hundred degrees Celsius. Consequently, rock behaviors under and after high-temperature conditions are of high interest and still a challenge to scientists and engineers of different disciplines. High temperatures result in thermal stresses and mineral expansion as well as various changes of physical and mineralogical properties within rock bodies (Hajpal and Torok 2004; Tian et al. 2012a, 2013), and thus lead to micro-structure changes and micro-cracks development and extension (Den’gina et al. 1994; Dwivedi et al. 2008). These effects change rock mechanical properties such as elastic modulus and compressive strength under and after high-temperature treatment, from a macro point of view, compared to those at normal temperature. Therefore, corresponding high-temperature mechanical properties of rocks are of high relevance for successful implementation of underground rock engineering projects. Sandstone is a widely distributed sedimentary rock composed mostly of sand-sized minerals or rock grains cemented mainly by siliceous, argillaceous, or calcareous materials. Its mechanical properties depend highly upon the degree of cementation and grain composition which are affected by temperature and burial history. In this manuscript, a comprehensive review of international literature, including Chinese publications not available for the English-speaking scientific community so far, described elastic modulus, compressive and tensile strengths of sandstones under and after high-temperature treatment.

Carbon dioxide sorption capacities of coal gasification residues.

Underground coal gasification is currently being considered as an economically and environmentally sustainable option for development and utilization of coal deposits not mineable by conventional methods. This emerging technology in combination with carbon capture and sorptive CO2 storage on the residual coke as well as free-gas CO2 storage in the cavities generated in the coal seams after gasification could provide a relevant contribution to the development of Clean Coal Technologies. Three hard coals of different rank from German mining districts were gasified in a laboratory-scale reactor (200 g of coal at 800 °C subjected to 10 L/min air for 200 min). High-pressure CO2 excess sorption isotherms determined before and after gasification revealed an increase of sorption capacity by up to 42%. Thus, physical sorption represents a feasible option for CO2 storage in underground gasification cavities.

A Modified Mohr-Coulomb Failure Criterion for Intact Granites Exposed to High Temperatures

Rocks often experience high temperatures (several hundred degrees Celsius) due to underground operations, such as deep geological disposal of nuclear waste, geothermal heat extraction, CO2 geological storage and underground coal gasification as well as deep mining. Laboratory studies have shown that mechanical properties such as compressive strength, tensile strength, elastic modulus of rocks such as granite, marble and sandstone are dependent on temperature and temperature-history. Therefore, conventional failure criteria such as the Mohr-Coulomb criterion may not provide a good estimate of rock strength under high temperature conditions. In the present study, a thermo-mechanical modified Mohr-Coulomb failure criterion is proposed based on the extensive review and interpretation of mechanical properties of granites exposed to high temperatures. The deduced criterion takes into consideration the effects of thermal damage and confining conditions on rock strength. A numerical study indicates that the proposed criterion provides a higher quality for depicting rock strength under high temperatures compared to the conventional Mohr-Coulomb criterion. Moreover, according to analyses of the behavior of other rock materials exposed to high temperatures, this criterion is also suitable for other rocks.

Feasibility of utilizing wavelet phase to map the CO2 plume at the Ketzin pilot site, Germany

ABSTRACT Spectral decomposition is a powerful tool that can provide geological details dependent upon discrete frequencies. Complex spectral decomposition using inversion strategies differs from conventional spectral decomposition methods in that it produces not only frequency information but also wavelet phase information. This method was applied to a time‐lapse three‐dimensional seismic dataset in order to test the feasibility of using wavelet phase changes to detect and map injected carbon dioxide within the reservoir at the Ketzin carbon dioxide storage site, Germany. Simplified zero‐offset forward modelling was used to help verify the effectiveness of this technique and to better understand the wavelet phase response from the highly heterogeneous storage reservoir and carbon dioxide plume. Ambient noise and signal‐to‐noise ratios were calculated from the raw data to determine the extracted wavelet phase. Strong noise caused by rainfall and the assumed spatial distribution of sandstone channels in the reservoir could be correlated with phase anomalies. Qualitative and quantitative results indicate that the wavelet phase extracted by the complex spectral decomposition technique has great potential as a practical and feasible tool for carbon dioxide detection at the Ketzin pilot site.

Numerical simulations of enhanced gas recovery at the Załezcze gas field in Poland confirm high co 2 storage capacity and mechanical integrity = Des simulations numériques de récupération assistée de gaz sur un gisement de gaz de Załęcze en Pologne confirment les capacités de stockage de CO 2 élevées et l’intégrité mécanique dudit gisement

Natural gas from the Załęcze gas field located in the Fore-Sudetic Monocline of the Southern Permian Basin has been produced since November 1973, and continuous gas production led to a decrease in the initial reservoir pressure from 151 bar to about 22 bar until 2010. We investigated a prospective enhanced gas recovery operation at the Załęcze gas field by coupled numerical hydro-mechanical simulations to account for the CO2 storage capacity, trapping efficiency and mechanical integrity of the reservoir, caprock and regional faults. Dynamic flow simulations carried out indicate a CO2 storage capacity of 106.6 Mt with a trapping efficiency of about 43% (45.8 Mt CO2) established after 500 years of simulation. Two independent strategies on the assessment of mechanical integrity were followed by two different modeling groups resulting in the implementation of fieldto regional-scale hydro-mechanical simulation models. The simulation results based on application of different constitutive laws for the lithological units show deviations of 31% to 93% for the calculated maximum vertical displacements at the reservoir top. Nevertheless, results of both simulation strategies indicate that fault reactivation generating potential leakage pathways from the reservoir to shallower units is very unlikely due to the low fault slip tendency (close to zero) in the Zechstein caprocks. Consequently, our simulation results also emphasise that the supraand subsaliniferous fault systems at the Załęcze gas field are independent and very likely not hydraulically connected. Based on our simulation results derived from two independent modeling strategies with similar simulation results on fault and caprock integrity, we conclude that the investigated enhanced gas recovery scheme is feasible, with a negligibly low risk of relevant fault reactivation or formation fluid leakage through the Zechstein caprocks. Résumé— Des simulations numériques de récupération assistée de gaz sur un gisement de gaz de Załęcze en Pologne confirment les capacités de stockage de CO2 élevées et l’intégrité mécanique dudit gisement — Le gaz naturel du gisement de Załęcze, situé dans la structure monoclinale de la région des Sudètes au niveau du Bassin Permien sud, est produit depuis novembre 1973, moyennant quoi la production de gaz continue a donné lieu à une diminution de la pression initiale du réservoir de 151 bar à environ 22 bar en 2010. Nous avons effectué une étude prospective mettant en jeu une opération de récupération de gaz améliorée sur le gisement de gaz de Załęcze par des simulations Oil & Gas Science and Technology – Rev. IFP Energies nouvelles, Vol. 70 (2015), No. 4, pp. 655-680 Ł. Klimkowski et al., published by IFP Energies nouvelles, 2015 DOI: 10.2516/ogst/2015012 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. hydromécaniques numériques couplées et prenant en compte les capacités de stockage de CO2, l’efficacité de piégeage et l’intégrité mécanique du gisement, des roches couverture et des failles régionales. Les simulations hydrodynamiques réalisées indiquent une capacité de stockage de CO2 de 106,6 Mt avec une efficacité de piégeage d’environ 43 % (45,8 Mt de CO2) établie après 500 ans de simulation. Deux stratégies indépendantes pour l’évaluation de l’intégrité mécanique ont été suivies par deux équipes différentes donnant lieu à la mise en œuvre de modèles de simulation hydromécaniques de l’échelle du gisement jusqu’à l’échelle régionale. Les résultats de simulation basés sur l’application de différentes lois constitutives pour les unités lithologiques présentent des écarts de 31 % à 93 % pour les déplacements verticaux maximum calculés au niveau supérieur du réservoir. Toutefois, les deux stratégies de simulation montrent qu’une réactivation des failles susceptible de générer des voies de fuite potentielles du réservoir vers des unités moins profondes, est improbable du fait de la tendance à un faible glissement de faille dans les roches couvertures de Zechstein. Nos résultats de simulation soulignent également que les systèmes de failles supraet sous-salinifères du gisement gazier de Załęcze sont indépendants et vraisemblablement pas reliés hydrauliquement. Sur la base des simulations associées aux deux stratégies de modélisation indépendantes, et qui présentent des résultats similaires en matière d’intégrité des roches couverture et des failles, nous concluons que le schéma de récupération assistée de gaz étudié est réalisable, avec un risque négligeable de réactivation de la faille ou de fuite du fluide de formation à travers les roches couverture du Zechstein.

The First Post-injection Seismic Monitor Survey at the Ketzin Pilot CO2 Storage Site: Results from Time-lapse Analysis

The injection of CO2 at the Ketzin pilot CO2 storage site started in June 2008 and ended in August 2013. During the 62 months of injection, a total amount of about 67 kt of CO2 was injected into a ...

Techno-Economic Comparison of Onshore and Offshore Underground Coal Gasification End-Product Competitiveness

Underground Coal Gasification (UCG) enables the utilisation of coal reserves that are currently not economically exploitable due to complex geological boundary conditions. Hereby, UCG produces a high-calorific synthesis gas that can be used for generation of electricity, fuels and chemical feedstock. The present study aims to identify economically competitive, site-specific end-use options for onshore and offshore produced UCG synthesis gas, taking into account the capture and storage (CCS) and/or utilisation (CCU) of resulting CO2. Modelling results show that boundary conditions that favour electricity, methanol and ammonia production expose low costs for air separation, high synthesis gas calorific values and H2/N2 shares as well as low CO2 portions of max. 10%. Hereby, a gasification agent ratio of more than 30% oxygen by volume is not favourable from economic and environmental viewpoints. Compared to the costs of an offshore platform with its technical equipment, offshore drilling costs are negligible. Thus, uncertainties related to parameters influenced by drilling costs are also negligible. In summary, techno-economic process modelling results reveal that scenarios with high CO2 emissions are the most cost-intensive ones, offshore UCG-CCS/CCU costs are twice as high as the onshore ones, and yet all investigated scenarios except from offshore ammonia production are competitive on the European market.

Joint Research Project Brine: Carbon Dioxide Storage in Eastern Brandenburg: Implications for Synergetic Geothermal Heat Recovery and Conceptualization of an Early Warning System Against Freshwater Salinization

Brine was a scientific joint-project implemented to accompany a prospective CO2 storage site in Eastern Brandenburg, Germany. In this context, we investigated if pore pressure elevation in a CO2 storage reservoir can result in shallow freshwater salinization involving the conceptual design of a geophysical early warning system. Furthermore, assessments of a potential synergetic geothermal heat recovery from the CO2 storage reservoir and hydro-mechanical integrity were carried out. The project results demonstrate that potential freshwater salinization is strongly depending on the presence and characteristics of geological weakness zones. The integrated geophysical early warning system allows for reliable monitoring of these potential leakage pathways at different spatial and time scales.

Joint Research Project CO2MAN (CO2MAN Reservoir Management): Continuation of Research and Development Work for CO2 Storage at the Ketzin Pilot Site

The joint project CO2MAN (CO2 Reservoir Management) was a scientific programme accompanying geological CO2 storage at the Ketzin pilot site in the German Federal State of Brandenburg. The project which was funded by the German Federal Ministry of Education and Research (BMBF) from 1 September 2010 to 31 December 2013 enclosed six scientific institutions and seven industry partners. The Ketzin pilot site is the longest-operating on-shore CO2 storage site in Europe. In advance of the CO2MAN project, CO2 injection had already started in June 2008 and storage operation had been accompanied by one of the world’s most extensive scientific research and development programmes. The CO2MAN project took advantage of this unique potential of the site in order to answer further technical and scientific questions on CO2 storage and to inform about this highly debated technology. The CO2MAN project demonstrates safe geological CO2 storage at the Ketzin site on a pilot scale.