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This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 191670, “Wastewater Injection and Slip Triggering: Results From a 3D Coupled Reservoir/Rate-and-State Model,” by Mohsen Babazadeh, SPE, and Jon•Olson, SPE, The University of Texas at Austin, prepared for the 2018 SPE Annual Technical Conference and Exhibition, Dallas, 24–26 September. The paper has not been peer•reviewed. This paper presents a coupled 3D fluid-flow and geomechanics simulator developed to model induced seismicity resulting from wastewater injection. The simulator modeled several cases of induced earthquakes with the hope of providing a better understanding of such earthquakes and their dominant causal factors, along with primary mitigation controls. Implementation of rate-and-state friction to model friction weakening and strengthening during fault slip to accurately model earthquake occurrence, and an embedded discrete fracture model to efficiently model fluid flow inside the fault, are among the essential features of the simulator. The complete paper presents results from a combined model that brings together injection physics, reservoir dynamics, and fault physics to explain better the primary controls on induced seismicity. Introduction Since 2009, a substantial increase in the number of earthquakes in the central and eastern United States has occurred. Oklahoma has been one of the most affected regions, with several earthquakes of M•5+, including the Prague earthquake in 2011 and the Pawnee earthquake in 2016. This has prompted efforts to find and understand any correlation between oil and gas activity—mainly wastewater disposal—and the occurrence of the earthquakes. Induced or triggered seismicity associated with wastewater injection, mining, oil and gas extraction, and geothermal operations has been identified since the earthquakes at the Rocky Mountain Arsenal in 1960s. Fluid injection into subsurface formations can increase pore pressure, reduce the effective stress, and induce slip on faults. Laboratory studies show that the sliding displacement may enhance fracture transmissivity and create a hydraulic pathway through the formation. In an unconventional reservoir, the enhancement could lead to improved hydrocarbon production by using the slipped natural fractures. But in some formations, such as water-disposal aquifers, seismicity might be induced when faults are activated within the igneous basement. Seismicity induced by fluid injection is controlled by several groups of parameters (injection, reservoir, and frictional). A fundamental understanding of which factors are the most important in triggering slip in areas of active wastewater injection and disposal has been hampered by interrelationships between the various parameters, leading to suggestions of injection volume, rate, or pressure being the most important. However, necessary reservoir characteristics, such as size and permeability, are not well characterized at the well or in the subsurface, and remain the main challenge for deterministic models. Additionally, rupture nucleation on faults near a region of injection depends on rate-and-state and related physics. The literature contains many relevant seismicity studies, which are identified in the reference section of the complete paper. A 2D simulation of fluid flow inside the fault zone suggested that post-shut-in earthquakes are likely to occur nucleating at the fault edges. Using a similar numerical scheme, other researchers investigated the 2011 Prague earthquake sequence to model the delayed triggering mechanism between the M 4.8 fore-shock and M 5.6 main shock. The result of the study contributed to defining constraints on values of fault transmissivity, fault compliance, and rate-and-state frictional properties. Although expensive, these types of full-physics models are capable of characterizing reservoir and fault properties. A 3D simulation in 2015 modeled fault activation under direct injection into the fault during shale-gas hydraulic fracturing. It found that for brittle faults, the moment magnitude can be higher.
complete paper, displacement, Earthquake, fault distance, friction, hydraulic fracturing, Injection Rate, injector, Magnitude, permeability, pressure increase, produced water discharge, Reservoir Characterization, Simulation, simulator model wastewater-injection-induced seismicity, Upstream Oil & Gas
Country:
- Europe > Czechia > Prague > Prague (0.45)
- North America > United States > Texas > Travis County > Austin (0.25)
SPE Disciplines:
ABSTRACT: From 2009 to 2017, parts of Central America have experienced marked increases in the number of small to moderate sized earthquakes. For example three significant earthquakes (Mw>5) occurred near Prague, Oklahoma, United States in 2011. Some attribute these events to a natural origin, while some others have claimed that injection is the main cause. This study aims to understand the effect of water injection within Prague, Oklahoma to evaluate the potential for fluid flow along mechanical faults and fractures discontinuities and to explore the possibility of fault reactivation. A 3D coupled fluid-mechanical model is constructed in FLAC3D to study the effects of injection and the possibility of induced seismicity. To simulate the earthquake, a slip-weakening friction law is used to be able to capture sudden slip. The results show that possibility of induced seismicity in complex Pennsylvanian-age Wilzetta fault and Arbuckle group are dependent on many parameters such as geometry and architecture of faults, hydromechanical properties of faults and geologic units, and the assumed state of stress.
Arbuckle Group, central oklahoma, damage zone, displacement, Earthquake, enhanced recovery, fault plane, fault reactivation, Fault Zone, flow in porous media, Fluid Dynamics, fracture characterization, injection, mazkoori well, MPa, Oklahoma, permeability, pore pressure, Prague, Pressure Build-Up, reactivation, Reservoir Characterization, reservoir geomechanics, united state, Upstream Oil & Gas, wilzetta fault
Country:
- North America > United States > Oklahoma (1.00)
- Europe > Czechia > Prague > Prague (0.47)
Oilfield Places:
- North America > United States > Texas > East Gulf Coast Tertiary Basin > Wilcox Formation (0.99)
- North America > United States > Oklahoma > Anadarko Basin > Cana Woodford Shale Formation (0.99)
- North America > United States > Mississippi > East Gulf Coast Tertiary Basin > Wilcox Formation (0.99)
- (6 more...)
SPE Disciplines:
Summary Distribution of gravity, magentic and geothermal fields, and their anomalous features in Albanides onshore and in the Albanian Adriatic Shelf in this paper are presented. There are presented also a hydrographical-geothermal phenomenon in the Albanian Adriatic Sea area, which are correlated with Albanides geological setting. Key words: Geothermal, Gravity, Heat Flow, Interpretation, Magnetics. Introduction The Albanides represent the assemblage of the geological structures in the territory of Albania, and together with the Dinarides at the North and the Hellenides at the South, have formed the southern branch of the Mediterranean Alpine Belt. Integrated onshore and offshore regional geophysical studies have been performed for the exploration of the Albanides. Seismological studies, gravity and magnetic surveys, reflection seismic lines, geothermal studies, radiometric investigations, vertical electrical soundings and integrated well loggings represent the applied complex of the geophysical investigation. The structural analysis of the Albanides according to the integrated geophysical investigations, in the framework of the integrated interpretation with geological studies results is presented. Integrated oceanographic, hydrographic and hydrological observations and study have been carried out in the Adriatic and Ionian seas, and littoral areas. Methods Regional Gravity and Magnetic Mapping of Albanian onshore territory have been performed at the scale 1:200.000. For the western oil and gas bearing regions of Albania have the gravity map of Bouguer Anomaly at scale 1.100.000. The studies on the geothermal field and evaluation of the geothermal energy in Albania, in the framework of the preparation of “Atlas of Geothermal Resources in Albania”, were performed on the basis of temperature logs in the 84 deep oil and gas wells and in 59 shallow boreholes. The temperature was measured with either resistance or thermistor thermometers. The thermal inertia of these thermometers is 5-6 seconds and 3.5 seconds, respectively. Laboratory of Department of Geothermics of the Geophysical Institute, Czech Academy of Sciences, Prague the thermal conductivity of the rocks was determined. The heat-flow density was calculated. Heatflow density calculations were made for homogenous lithology part of geological sections, according to several models. The temperature maps at 100, 500, 1000, 2000, 3000 meters depths, average geothermal gradient map, heat flow density map and geothermal zones map, by the processed data were compiled. The maps of the Albanian territory have been linked with Greek and Adriatic space ones. Estimation of the geothermal resources of the thermal zones has been performed, based on a volumetric heat content of the model assuming exploitation of geothermal energy by a doublet or a singled wells system. Oceanographic, hydrographical and hydrological studies are based on multi annual observations in the hydrometric station network since 1958 and on two Albanian oceanographic expeditions “Saranda-1963” and “Patos- 1964” in the Southern Adriatic and Northern Ionian. The objects of these studies were: water levels, temperatures and chemical content, formation and circulation of the water mass, wave and wind regimes of the Adriatic and Ionian coastline, water potential and run-off discharge regime of the Albanian Mountainous River System into the Adriatic Sea, suspended material discharge; alluvial granulometric composition, water chemical composition etc.
Academy, Albania, Albanide, alpine mediterranean folded belt, anomaly, crust, external albanide, fracture, Frashëri, geothermal energy, Institute, interpretation, ophiolitic belt, polytechnic university, renewable energy, Reservoir Characterization, seg houston 2005, structural geology, tectonic zone, Tirana, Upstream Oil & Gas
Geophysics:
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Magnetic Surveying (1.00)
- Geophysics > Gravity Surveying (0.88)
Oilfield Places:
- Europe > Italy > Adriatic Sea > Adriatic Basin (0.99)
- Europe > Albania > Ionian Basin (0.99)
SPE Disciplines:
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Reservoir Description and Dynamics > Non-Traditional Resources > Geothermal resources (1.00)
ABSTRACT Between the German city of Dresden and the Czech capital Prague a 4-lane highway is under construction. At the outskirts of Dresden it will cross the narrow and deeply eroded Weißeritz Valley by a bridge. Two twin tube tunnels under oblique angles join the bridge out of the rocky valley flanks. The different geotechnical conditions of these 4 tunnel portals, their design and construction are described within this publication. The two southern portals of the tunnel Dölzschen are situated within a vertical 65 m high former quarry slope, 25 m above the valley floor. The slope proved instable due to toppling failure and exposed serious rockfall risks. Systematic anchoring, scaling, rock bolting, netting and filling under extreme access conditions eliminated these risks. Tunnel excavation started from the slope surface without any precut or conventional portal construction. The opposite northern portals of the tunnel Coschuetz are situated in more gentle rock slopes. After removal of debris, excavation of the eastern tunnel started in a 30° slope striking oblique to the driving direction, without any precut, too. Because of the gentle slope inclination the cross section was not earlier completely covered by rock than 30 m behind. Zusammenfassung Der Neubau der Bundesautobahn A 17 wird Dresden und Prag miteinander verbinden. Die vierspurige Autobahn quert westlich von Dresden das enge und tief eingeschnittene Tal der Wilden Weißeritz mit einer Bruecke. An beide Brueckenwiderlager schließen mit schiefwinkligem Anschnitt doppelröhrige Tunnel an, deren Portale in den felsigen Talflanken liegen. Die unterschiedlichen geotechnischen Verhaltnisse, die Überlegungen fuer einen jeweils optimalen Entwurf und der Bau der portalnahen bergmannischen Tunnelabschnitte sind Gegenstand dieser Veröffentlichung. Die Suedportale des Tunnels Dölzschen liegen in einer vertikalen, 65 m hohen Felswand, 25 m ueber dem Talgrund. Die Felswand erwies sich als global kippgefahrdet, außerdem lagen flachig verteilte erhebliche Steinschlag- und Felssturzrisiken fuer Bau und Betrieb vor. Die Kippgefahr wurde durch ein Systemraster aus vorgespannten Felsankern, die Steinschlag- und Felssturzrisiken durch bergsteigerisches Beraumen mit dem Brecheisen, Felsnagel und Steinschlagschutznetze eliminiert. Der Tunnelausbruch begann von einer Vorschuettung direkt in der Felswand ohne Voreinschnitt im Schutz einer kurzen Luftbogenstrecke. Die gegenueberliegenden Nordportale des Tunnels Coschuetz befinden sich in wesentlich flacheren Hangen. Nach dem Aushub einer mehrere Meter dicken Abraumhalde begann der Tunnelausbruch der östlichen Röhre asymmetrisch mit einer Luftbogenstrecke in einer spitzwinklig zur Vortriebsrichtung streichenden, 30° mit dem Vortrieb steigenden Felsflache, ebenfalls ohne Voreinschnitt. Resume Par la construction de l'autoroute A 17 les villes de Dresden et Prague seront reliees. Cette autoroute traverse la vallee etroite et profonde de la rivière Weißeritz par un pont, près de la ville de Dresden. Aux deux boutes du pont commencent en coup oblique deux tunnels dont les portails se trouvent dans des pentes rocheuses. Les conditions geotechniques differentes, les considerations d'obtenir des designs optimaux et la construction de ces portails selon des differents designs sont objets de cette publication. Les portails du sud du tunnel Dölzschen sont situes 25 m sur le fond de la vallee dans une pente rocheuse verticale d'une hauteur de 65 m. La pente ne se prouvait pas suffisamment stable contre le basculement et exposait des risques sevères de chutes de pierres. La securite contre le basculement etait produite par un système d'ancres precontraintes, le risque de chutes de pierres etait elimine par enlever les blocs instables en grimpant avec le pince- monseigneur, par des ancrages et par des filets de protection contre les chutes de pierres. Le creusement des tunnels commençait immediatement dans la pente, sans une pretranchee courte sous la protection d'un tronçon avec cintres poses à ciel ouvert. Introduction To fasten traffic between the Czech Republic and Germany a new highway is under construction, connecting the Czech capital Prague to the German highway system. Near Dresden the new highway crosses a narrow and deeply eroded valley. The highway comes from the north through the 600 m long Dölzschen Tunnel, crosses the valley by the 280 m long Weißeritz Bridge, 35 m above its ground, and leaves it through the 2.300 m long Coschuetz Tunnel. Both tunnels are twin tubes, having a width of 16 m and a height of 12 m. Fig. 1 shows the situation. The Weißeritz valley is cut into very hard Syenodio-rites and is narrow, therefore. Both valley sides expose rock slopes. The right or southern one has a natural inclination between 25 and 35° with vertical cliffs up to 15 m high. Down from the crest the eastern part of the slope is covered by debris from a quarry behind the crest. The left or northern valley side was occupied by another quarry transforming the natural slope to a 65 m high vertical artificial rock slope. The portals had to be constructed within these slopes.
ABSTRACT: Within the last 20 years, there has been an intense research activity within the problems of radioactive waste isolation in underground repositories all over the world. The principle of waste isolation is based on a multi-barrier system that is composed of two basic components – engineered and natural barriers. It is assumed that the main material to be used for the engineered barrier structure will be bentonite. The research on bentonite therefore needs to be done with due complexity, with regards to the multi-disciplinary character of the problem, but namely with a view to the target demand: the design of the engineered barrier structure with a guaranteed, extremely long-term safe function (hundreds of thousands of years). This paper describes the necessary scope of geotechnical part of research, presenting experimental research carried out at the Centre of Experimental Geotechnics of the Czech Technical University in Prague. INTRODUCTION The research on the problems of high-level nuclear waste disposal in underground repositories was launched in 1955, when the conference on peaceful exploitation of nuclear energy in Geneva became the forum for formulating the principal ways of radioactive waste disposal. Specialised workplaces were gradually set up all over the world concentrating research experts in many scientific branches. The problems of radioactive waste isolation in underground repositories are of a highly multi-disciplinary character. Despite the intensive on-going world-wide research performed within this problem area within the last 20 years, not all has been satisfactorily solved today. Whereas the required functionality, service life or safety for standard engineering structures range within the maximum limits of dozens of years, high-level nuclear waste has to be isolated for all the time when it remains hazardous to any component of the environment, that is for the period of hundreds of thousands of years.
Industry:
- Water & Waste Management > Solid Waste Management (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
SPE Disciplines:
ABSTRACT: In Northern Bohemia, a new motorway crosses non-engineered landfills of clayey spoil from open cast coal mines. Recent fills are soft, unconsolidated, double porosity medium, originally consisting of lumps of typical dimensions from a few millimetres to a few hundred millimetres. The age of the fills is about 20 to 30 years and over this period they generally remained unsaturated down to the depths of 15 to 20 metres. Laboratory experiments with a model double porosity clayey material revealed high susceptibility to collapse. The site investigation involved both laboratory and in-situ testing. However, neither standard in-situ nor laboratory testing was believed to be representative enough for the field behaviour of the fill. Therefore an instrumented trial embankment was built on a site with about 30 metres of clayey fill. The settlement was found to be confined to the upper 20 metres of the fill. INTRODUCTION In Northern Bohemia, a new motorway between Prague (Czech Republic) and Dresden (Germany) has to cross a coal basin. The coal seam, which is up to 30 metres thick, is overlain by Tertiary overconsolidated clays and claystones. In the 20th century, the original roof-fall underground exploitation of the coal was replaced by large scale open cast mining, which reaches down to depths of about 150 metres. The spoil of the Tertiary clay and claystone has been dumped either in the open pits or in their neighbourhood. Some of these non-engineered fills reach a height over 100 metres. In some places, fly ash and municipal waste had been also deposited in the pits. On the periphery of the landfills, landslides are frequent. The largest one, involving about 140 million cubic metres, occurred in the coal basin area in 1985, as a consequence of the pore pressure build-up in a recent landfill.
double porosity clayey material, embankment, fragmentary clay, laboratory, laboratory testing, landfill, metals & mining, motorway, oedometer test, reference point, Reservoir Characterization, saturation, settlement, site investigation, specimen, transition, trial embankment, triaxial apparatus, University, Upstream Oil & Gas
ABSTRACT: : The article deals with methodical approach towards design and realization of the first underground natural gas storage in the Czech Republic. The gas is stored in newly mined network of galleries about 1000 m under the surface with total volume of 620.000 m and total area of 1,3 km. Compact granite massif enabled storage construction without hydraulic barrier. Geotechnical investigations, methodology of tests in underground laboratory and their results are briefly described. RÉSUMÉ: : L'article rend compte de l'approche methodique dans la determination et la realisation du premier reservoir souterrain de gaz naturel en Republique Tcheque. Le gaz est deverse dans un reseau de galeries nouvellement creusees à une profondeur de 1000 m sous la surface du sol et d'un volume de 620.000 m, sur une surface de 1,3 km. Un massif granitique de qualite a permis la realisation d'un reservoir sans barriere hydraulique. Les sondages geotechniques, la methodologie des essais dans le laboratoire souterrain et les resultats sont succinctement exposes. ZUSAMMENFASSUNG: : Der Artikel behandelt den methodischen Standpunkt zum Entwurf und zur Ausfilhrung des ersten unterirdischen Erdgasspeichers in der Tschechischen Republik. Das Gas ist im neu ausgebrochenen Stollennetz in 1000 m Tiefe unter der Gelandehohe mit Volumen von 620.000 m beim Flachenausmaß von 1,3 km gespeichert. Das hochwertige Granitmassiv ermöglichte die Speicherausfuehrung ohne den Einsatz von hydraulischer Sperre. Es werden kurz die geotechnische Untersuchung, Verfahrensweise der Pruefungen in Tieflabor und Ergebnisse beschrieben. GEOGRAPHICAL AND GEOLOGICAL SITUATION Construction of underground cavern-type natural gas storage was completed in Pribram (CZ) ore mining district in 1998. The storage is situated in centralbohemian plutone granitoides about 1,000 meters under the surface. There are 100 parallel galleries which have been mined out from development cross cuts in east and west direction. The total ground area of the storage is 1,250 × 1,050 meters. Gas storage at 9.5 MPa has been originally expected. Geotechnical investigation results have however shown that the storage pressure could be increased up to 12.5 MFa and that it would not be necessary to establish artificial hydraulic barrier with respect to the quality of surrounding rock masif. The purpose of the storage is to provide the natural gas supplies during peak consumption periods for Prague and for the area of Central Bohemia. A number of suitable locations has been preliminary selected for storage construction. Two of these locations have been situated in Proterozoic rock masses. Number of potential locations has been reduced to three later on. The first location has been situated in separate magmatic plutonic object in the Bohutin area. Surrounding rock massif consisted of autometamorphosed siliceous diorite. Two other locations have been situated in central-bohemian plutone near Milin and Konĕtopy - Buk villages (Přibram region). Existing winnings had been utilized in all three cases. There were abandoned polymetalic ore and uranium ore mines in Bohutin and Haje and underground prospecting shaft in Milin, Horizontal prospecting cross cuts have been mined out in required depth in all shafts and special geotechnical tests have been performed at these cross cuts.
borehole, cavern-type underground natural gas storage, construction, cross cut, Fault Zone, gallery, gas storage, geotechnical investigation, hydraulic barrier, investigation, laboratory, massif, Midstream Oil & Gas, MPa, natural gas storage, objective, perpendicular, rock massif, shaft, storage construction, Upstream Oil & Gas
SPE Disciplines: Reservoir Description and Dynamics > Storage Reservoir Engineering > Natural gas storage (1.00)
Ludek Klimes*, Department of Geophysics, Charles University Prague, Czech Republic Summary Explicit approximate equations describing the physical meaning of the migrated sections are derived. The imaged combination of elastic parameters (reflectivity) depends on the selection of the polarizations of the incident and back-propagated wavefields and on the directions of propagation. The migrated section is then approximately the convolution of the unknown exact reflectivity with the resolution function depending on the aperture and on the form of the imaging time function. Introduction A general formulation of prestack migration based on imaging (mapping) incident and scattered wavefields, extrapolated into the macro-model by arbitrary numerical methods (Claerbout 1971) is considered. A common shot prestack migration is assumed since it is the most natural configuration from the physical point of view, although the same approach could simply be applied to other configurations.
approximate incident wavefield, back-propagated wavefield, decomposition, equation, geological structure, material parameter, migrated section, migration, prestack seismic migration, receiver area, reflection coefficient, Reservoir Characterization, resolution, resolution function, seismic migration, spatial resolution, target zone, Upstream Oil & Gas, wavefield
SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
Summary The attenuation of electromagnetic waves depends on the electric parameters of the medium, in which they propagate. By means of laboratory measurements the dependence of these parameters on the pressure was found. These dependences are not simple. It is possible to follow the changes of the electric parameters both according to the size and according to the direction of the active outer force. On base of these experimental measurements a measuring method for finding pressure changes in rock masses according to the attenuation changes of the electromagnetic waves has been suggested. To reach this aim the measuring apparatus KAP A—1 for one purpose was designed. The function of the measuring device was tested in the mining conditions in the iron ore mine south-west from Prague (Czechoslovakia). To prove the theoretically derived dependences of the attenuation of the electromagnetic waves on the pressure in the rocks, the long-termed measurement in the deep seated mine eastwards from Prague was done. The measuring apparatus was placed in the cross cut from the deposit to the overburden and the dependence of the pressure changes in the overburden with the face approaching to it was investigated. The results of the measurements proved the dependence of the attenuation changes of the electromagnetic waves on the pressure changes of the rock masses in the line of the wave propagating. The suggested method can be used for following the state of tension in the pillars, ceilings and in other parts of mine. To place the measuring apparatus in the investigated area it was necessary to excavate the cross cut, the presence of which may disturbe the pressure state of rock masses to considerable extent. That is why such a construction of measuring apparatus has been considered, that will be able to be placed into the bore-hole. One of the main problems, the rock mechanics has been dealing with, is rock pressure measurement. To this purpose a series of physical dependences has been used of, including e.g. : dependence of the seismic wave propagation on the pressure, dependence of the attenuation of y radiation on the pressure and dependence of the resistance of the direct electric current. In our institutes the dependence of the attenuation of the electromagnetic waves in the medium, in which they propagate, was used of to the measurement of pressure changes.
amplificateur, Amplifier, apparatus, attenuation, changement, conductivity, dependence, electromagnetic wave, frequency, hf amplifier, impedance, iron mining, long-termed stability, metals & mining, Prague, receiver, receiver pa, relation, Reservoir Characterization, seismic surveying, stability, structural geology, tension change, transmitter, Upstream Oil & Gas, voltage
Summary In the area of Prague the bedrock is built up dominantly of Ordovician complexes showing different lithological character. Argillaceous shales alternate with arenaceous shales, greywackes and quartzites. This alternation of pelitic and psammitic rocks is interpreted in terms of the oscillation of the sea level during the Ordovician. The individual complexes differing in lithology repeat several times owing to the recurrence of analogous sedimentary conditions. The physico-mechanical properties of Ordovician rocks are controlled mainly by their lithological character and tectonic disturbance. In addition, the surface layers of the bedrock were disturbed by deep freezing during the Pleistocene, when the area under consideration was situated within the periglacial zone. The differing physicomechanical properties of the bedrock in the Prague area called forth the necessity of determining the deformational properties of rocks by in situ loading tests as early as in 1928. The results obtained by several tens of loading tests, which have been carried out on the Ordovician shales, make it possible to estimate the mechanical properties of rocks on the basis of their geological characteristics. Resume Le soubassement rocheux de la region de Prague est forme, pour la plupart, par des couches ordoviciennes d'un developpement lithologique different. Les schistes argileux et sableux, grauwackes et quartzites y sont deposes alternativement. Cette alternance de roches pelitiques et psammitiques s'explique par des fluctuations du niveau de la mer pendant l'Ordovicien. Les conditions de sedimentation se sont repetees à cette epoque plusieurs fois, si bien que plusieurs complexes d'un caractere lithologique different se sont formes. Les proprietes physico-mecaniques des roches ordoviciennes sont influencees surtout par le caractère lithologique et les accidents tectoniques. En outre, une alteration intense se manifestait à la surface du soubassement rocheux, alteration due à la gelification du sol pendant le Pleistocène, quand le territoire de Prague se trouvait dans la region periglaciaire. Cette alteration a aussi une influence considerable sur la deformabilite de la roche. A cause du caractère physico-mecanique different des roches dans Ie soubassement de Prague il etait necessaire d'en etudier les qualites de deformation par epreuve de charge dejà depuis 1928. Les resultats de plusieurs dizaines des epreuves de charge, executees depuis cette epoque jusqu'à present, permettent de prevoir les qualites de deformation à la base d'une appreciation geologique du type de roche respectif. Zusammenfassung Der Felsuntergrund in Prager Raum besteht vorwiegend aus lithologisch bunt ausgebildeten Schichtenfolgen des Ordoviziums, die durch Wechsel von Ton- und Sandschiefer, Grauwacken und Quarziten gekennzeichnet sind. Dieser wird auf die Meeresschwankungen wahrend des Ordoviziums zurueckgefuehrt und kommt in der zyklischen Wiederholung von pelitischen und psamitischen Gesteinen zum Vorschein. Die physikalmechanische Eigenschaften dieser Gesteine sind hauptsachlich durch den lithologischen Charakter und die tektonische Störungen Beeinflusst. Daneben ist die Felsoberflache infolge der tiefen Frostwirkung im Pleistozan, als sich das Prager Gebiet in der periglazialen Zone befand, tief verwittert. Die Deformationseigenschaften gehen auch auf diese Verwitterung stark zurueck. Der verschiedene physikal-mechanische Charakter des Felsuntergrunds in Prag hat schon im Jahre 1928 die Notwendigkeit erfordert, die Deformationseigenschaften mit Hilfe von Belastungsversuchen in situ zu bestimmen. Aus den Ergebnissen von einigen Zehn Belastungsversuchen der ordovizischen Schiefer, die seit dieser Zeit durchgefuehrt worden sind, kann man auf deren Deformationseigenschaften aufgrund der geologischen Beurteilung des betreffenden Gesteinstypus schliessen. The city of Prague is situated in a deep valley of the Vltava River, which is carved in the folded Early Paleozoic, prevalently Ordovician rocks. The ground is covered with superficial deposits, such as remnants of river terraces, slope debris, loess etc. of a small thickness. Therefore, all industrial plants and large buildings with deep basements reach down into the bedrock. The Ordovician shales provide a foundation soil of different properties which depend on their lithological composition, tectonic disturbance and weathering. These conditions called forth already in the 'thirties a need of fairly precise methods for the determination of the mechanical properties of rocks, their bearing capacity and compressibility in particular. Both these qualities were determined by in situ loading tests. These have been used up to the present for the establishment of elastic and deformational characteristics, so that the results of several tens of tests made at that time are now available for the preliminary evaluation of the rocks under consideration. Geological characteristics of the Ordovician beds The Ordovician complexes of the Prague area consist of regularly alternating thick layers of clayey shales and arenaceous layers usually developed as quartzites. The alternation of pelitic and psammitic sediments suggests an oscillation of the sea bottom, i. e. an epeirogenic unrest at the time of their deposition. The recurrent sedimentary conditions are responsible for the recurrence of rocks analogous in lithological character and physico-technical properties throughout the Ordovician. From the biostratigraphical point of view, the rocks of the Prague area are ranged to the Middle Ordovician (Llanvirnian and Llandeilo) and the Upper Ordovician (Caradoc) and are further subdivided on paleontological evidence.
argillaceous shale, bedrock, compressibility, deformation, determination, disturbance, elasticity, loading test, mechanical property, moduli, ordovician rock, Ordovician shale, Prague, quartzite, Reservoir Characterization, settlement, shale, situ loading test, structural geology, technical property, Upstream Oil & Gas, weathered rock
Geologic Time:
- Phanerozoic > Paleozoic > Ordovician (1.00)
- Phanerozoic > Cenozoic > Quaternary > Pleistocene (0.46)
SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
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