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Mechanical and microstructural data used in the article Pijnenburg et al., Deformation behaviour of sandstones from the seismogenic Groningen gas field: Role of inelastic versus elastic mechanisms

Hydrocarbon or groundwater production from sandstone reservoirs can result in surface subsidence and induced seismicity. Subsidence results from combined elastic and inelastic compaction of the reservoir due to a change in the effective stress state upon fluid extraction. The magnitude of elastic compaction can be accurately described using poroelasticity theory. However inelastic or time-dependent compaction is poorly constrained. We use sandstones recovered by the field operator (NAM) from the Slochteren gas reservoir (Groningen, NE Netherlands) to study the importance of elastic versus inelastic deformation processes upon simulated pore pressure depletion. We conducted conventional triaxial tests under true in-situ conditions of pressure and temperature. To investigate the effect of applied differential stress (σ1 – σ3 = 0 - 50 MPa) and initial sample porosity (φi = 12 – 25%) on instantaneous and time-dependent inelastic deformation, we imposed multiple stages of axial loading and relaxation. The obtained data include: 1) Mechanical data obtained in conventional triaxial compression experiments performed on reservoir sandstone. In these experiments, we imposed multiple stages of active loading, each followed by 24 hours of stress relaxation. 2) Microstructural data obtained on undeformed and deformed samples.

Experimental rock physics for the calibration of seismic-data interpretation: The case of the borehole Humilly-2 (France) in the Geneva area

This dataset is associated with the publication of Hefny, M., et al. (2020) A laboratory approach for the calibration of seismic data in the western part of the Swiss Molasse Basin: the case history of well Humilly-2 (France) in the Geneva area”. It includes data on mineralogical composition and experimental ultrasonic waves velocity measurements. It contains also seismic parameters calculated for the above-mentioned data. The measurements were performed as part of a database collection (SAPHYR) under the umbrella of the Swiss Commission of Geophysics (SGTK) and a project of the Canton of Geneva (GEothermie 2020), implemented by Services Industriels de Genève (SIG) for geothermal energy development (Moscariello 2019).

Mechanical and microstructural data used in: “Inelastic deformation of the Slochteren sandstone: Stress-strain relations and implications for induced seismicity in the Groningen gas field"

Pore pressure reduction in sandstone reservoirs generally leads to small elastic plus inelastic strains. These small strains (0.1 – 1.0% in total) may lead to surface subsidence and induced seismicity. In current geomechanical models, the inelastic component is usually neglected, though its contribution to stress-strain behaviour is poorly constrained. To help bridge this gap, we performed deviatoric and hydrostatic stress-cycling experiments on Slochteren sandstone samples from the seismogenic Groningen gas field in the Netherlands. We explored in-situ conditions of temperature (T = 100°C) and pore fluid chemistry, porosities of 13 to 26% and effective confining pressures (≤ 320 MPa) and differential stresses (≤ 135 MPa) covering and exceeding those relevant to producing fields. The findings of our work are outlined in the corresponding paper. The data presented here are the measured mechanical tabular data and microstructural data (stitched mosaic of backscatter electron images) provided as uncompressed jpg images. In addition, for one sample we include chemical element maps obtained through Electron Dispersive X-ray spectrometry (EDX).

Anpassungsfähigkeit annueller Arten und ihre Bedeutung für die Phytodiversität der Kulturlandschaft

Die Rote Liste der gefährdeten Pflanzen Deutschlands weist die Gruppe der annuellen Arten der Segetalflora als die am stärksten gefährdete Artengruppe in Deutschland aus. Als Gefährdungsursache steht die moderne Landbewirtschaftung mit der Verwendung von Herbiziden und Mineraldünger, verbesserter Saatgutreinigung, Vereinfachung der Fruchtfolgen, frühem Stoppelumbruch und der Aufgabe von Grenzertragsstandorten im Mittelpunkt. Schutzbemühungen, wie Erhaltungskulturen in Botanischen Gärten und Feldflorareservaten haben eine Art musealen Charakter. Auch die Einrichtung eines bundesweiten Netzwerkes von Schutzäckern mit langfristigen Bewirtschaftungsverträgen trägt letztendlich nur punktuell zur Erhaltung der Segetalzönosen bei. Eine erfolgreich praktizierte Variante des flächendeckenden Ackerwildkrautschutzes stellen die Ackerrandstreifenprogramme der Bundesländer dar. Durch den Verzicht auf Herbizide und zum Teil auch auf mineralischen Dünger können sich hier die Segetal-Arten erhalten, die in der Samenbank vorhanden sind. Die aktuelle Entwicklung zeigt aber einen Rückgang der Ackerrandstreifenprogramme und eine zunehmende Popularität von Blühstreifen. Die primäre Absicht bei der Anlage von Blühstreifen ist jedoch der Schutz von Bienen und Niederwild. Werden die Blühstreifen auf Ackerflächen verwendet, so unterdrücken die Ansaatmischungen die Wildkrautflora und damit verschlechtert sich die Situation der ursprünglich in Ackerrandstreifen vorkommenden Ackerwildkräuter. Die sich durch den Menschen immer wieder verändernde Landnutzung ist von Beginn an mit einer Anpassung der Vegetation einhergegangen. Einen ähnlichen Anpassungsprozess werden die Veränderungen der klimatischen Verhältnisse in Mitteleuropa im Zuge der globalen Erwärmung mit sich bringen. Ziel des Projektes ist es daher die Anpassungsfähigkeit von Ackerwildkräutern an die durch Nutzungs- und Klimawandel herbeigerufenen Änderungen der vorherrschenden Standortbedingungen zu untersuchen. Darauf aufbauend sollen angepasste Schutz- und Wiederansiedlungskonzepte entwickelt werden.

FP1-ENNONUC 3C, Determination of physical properties on the core material of the borehole soultz sous foret (Soultz Project)

Objective: Aim: to determine the physical properties of the granitic basement in the soultz hdr borehole. General information: description: the core samples obtained from the granite section of the soultz gpk-1 borehole will be analysed to determine the properties of the granite such as strength and fracture toughness, thermal parameters, heat production (radiogenic content), and acoustic, electrical and magnetic properties. Achievements: The results of studies carried out on cores and cutting materials of three boreholes to a depth of 3.6 km are summarised. The physical property programme included measurements of density, ultrasonic velocities, seismic anisotropy, elasticity, fracture behaviour, electric and magnetic parameters, thermal properties including radioactive heat production, and radioactive age dating. Heat production in the Soultz granite is 2 to 3 times greater than that in other granites at the surface, although all surface granites in the vicinity show the same intrusion age. The physical property measurement programme has demonstrated that continuous measurements on cores and cuttings are essential for both operational drilling procedures and down hole condition assessment in crystalline rock formations. The European Geothermal Project involved teams from France and Germany who collaborated to test a site in the Upper Rhine Valley for its suitability for terrestrial heat mining (hot dry rock (HDR) energy production). Some British scientists participated in specific tasks. The site was chosen near Soulz-sous-Forets in Alsace at the location of the old oil field of Pechelbronn which was the first oil field exploited in Europe since the 18th century. It is situated on 1 of the summits of a very large thermic anomaly (200 km long and 20 km wide) where the mean geothermal gradient between the surface and 1500 m is known to be higher than 6.5 C/100 m. The programme began in July 1987 with a 2000 m deep borehole. Below at 1375 m thick sediment cover, the granitic basement was penetrated to a depth of 2000 m. The temperature at the bottom of the hole was 140 C. The geothermal gradient within the sediments was unusually high (10 C per 100 m) and diminished to a normal after a series of fractures inside the Buntsandstein producing some water at 116 C with a total salinity 98 g/l. At the depth of 1820 m, hydraulically active natural fissure was reached. The artesian outflow from this zone was 0.15 l/s, with well head pressure of 1.6 bars. The thermal water produced from the well had a high chloride contents and clearly had an identical origin with the fluid collected from the Buntsandstein just above the granite. During the water injection tests, a second active natural fissure was detected normally closed out but which seemed to aquire a noticeable permeability at a well head pressure of about 40 bars.

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