Seal capacity estimation from subsurface pore pressures   总被引：1，自引：0，他引：1  

Hege M. Nordgård Bolås  Christian Hermanrud  Gunn M. G. Teige 《Basin Research》2005,17(4):583-599

A cap rock's capacity to seal hydrocarbons depends on its wettability and the sizes of the pore throats within the interconnected pore system that the leaking hydrocarbons must penetrate. These critical pore throat sizes are often poorly constrained in hydrocarbon exploration, partly because measurements of pore throat sizes have not been performed, and partly because pore throat measurements on a few individual samples in the cap rock may not be representative for the seal capacity of the top seal as a whole. To the contrary, the presence of formation overpressure can normally be estimated in drilled exploration targets. The presence of overpressure in reservoirs testifies to small pore throats in the cap rocks, as large pore throats will result in sufficiently high cap rock permeability to bleed off the overpressure. We suggest a stepwise procedure that enables quantification of top seal capacities of overpressured traps, based on subsurface pressure information. This procedure starts with the estimation of cap rock permeabilities, which are consistent with observed overpressure gradients across the top seals. Knowledge of burial histories is essential for these estimations. Relationships between pore throat size and permeability from laboratory experiments are then applied to estimate critical pore throat diameters in cap rocks. These critical pore throat diameters, combined with information of the physical properties of the pore fluids, are then used to calculate membrane seal capacity of cap rocks. Estimates of top seal capacity based on this procedure are rather sensitive to the vertical fluid velocity, but they are also to some extent sensitive to inaccuracies of the pore throat/permeability relationship, overpressure gradient, interfacial tensions between pore fluids, hydrocarbon density and water viscosity values. Despite these uncertainties, applications of the above‐mentioned procedure demonstrated that the mere presence of reservoir overpressures testifies to sufficient membrane seal capacity of cap rocks for most geological histories. Exempt from this statement are basins with rapid and substantial sediment compaction in the recent past.  相似文献   

Fabric studies within the Cascade Lake shear zone, Sierra Nevada, California   总被引：1，自引：0，他引：1  

Basil Tikoff  Matthew R. Davis  Christian Teyssier  Michel de St. Blanquat  Guillaume Habert  Sven Morgan   《Tectonophysics》2005,400(1-4):209-226

The Cascade Lake shear zone occurs on the eastern margin of the Tuolumne Intrusive Suite, Sierra Nevada Batholith, California. Foliation in the zone is NNW trending and subvertical, and lineation is moderately south plunging. Deformation is syn-tectonic with emplacement of the Cathedral Peak granodiorite. A deformation gradient exists toward the NE margin of this pluton, with higher strains and lower temperatures of deformation found near the contact. We compare fabric data collected very densely in this shear zone using several techniques: field fabrics, 3D orientation of K-feldspar megacrysts, and AMS (anisotropy of magnetic susceptibility) analysis. In general, the results from the three different methods are in agreement. Deformation in this shear zone is part of a larger pattern of deformation within the Cathedral Peak granodiorite, as recorded by AMS analysis, and dextral shearing associated within the last stage of plutonism within the Sierra Nevada magmatic arc.  相似文献   

Thermal evolution of an extensional detachment as constrained by organic metamorphic data and thermal modeling: Graz Paleozoic Nappe Complex (Eastern Alps)   总被引：1，自引：0，他引：1  

Gerd Rantitsch  Reinhard F. Sachsenhofer  Christian Hasenhüttl  Barbara Russegger  Thomas Rainer 《Tectonophysics》2005,411(1-4):57-72

Following Early Cretaceous nappe stacking, the Eastern Alps were affected by late-orogenic extension during the Late Cretaceous. In the eastern segment of this range, a Late Cretaceous detachment separates a very low- to low-grade metamorphic cover (Graz Paleozoic Nappe Complex, GPNC) above a low- to high-grade metamorphic basement. Synchronously, the Kainach Gosau Basin (KGB) collapsed and subsided on top of the section.Metamorphism of organic material within this section has been investigated using vitrinite reflectance data and Raman spectra of extracted carbonaceous material. In the southern part of the GPNC, vitrinite reflectance indicates a decrease in organic maturity towards the stratigraphic youngest unit. The remaining part of the GPNC is characterized by an aureole of elevated vitrinite reflectance values and Raman R2 ratios that parallels the margins of the GPNC. Vitrinite reflectance in the KGB shows a steep coalification gradient and increases significantly towards the western basin margin. The observed stratigraphic trend in the southern GPNC is a result of deep Paleozoic to Early Cretaceous burial. This maturity pattern was overprinted along the margins by advective heat and convective fluids during Late Cretaceous to Paleogene exhumation of basement rocks.During shearing, the fault zone was heated up to ca. 500 °C. This overprint is explained by a two-dimensional thermal model with a ramp-flat fault geometry and a slip rate of 1 to 1.5 cm/year during 5 Ma fault movement. The collapse basin above the detachment subsided in a thermal regime which was characterized by relaxing isotherms.  相似文献   

The Cambridge Guide to the Solar System     

Christian Koeberl 《Geochimica et cosmochimica acta》2005,69(11):2945

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Environmental policy reform on north-eastern Brazil’s agricultural frontier     

Christian Brannstrom 《Geoforum》2005,36(2):257-271

The expansion of modern agriculture in developing countries presents numerous challenges for environmental policy makers. Environmental policies for agriculture in north-eastern Brazil’s soybean belt are analyzed, with emphasis on the role of a non-state actor in leading policy reforms. An organization representing large farmers is leading policy reforms to reduce the environmental impacts of modern agriculture. By contrast, state agencies are relatively weak and ineffective. The analysis situates this question conceptually in literatures stressing the political and structural causes of corporate environmentalism and literatures explaining the increasingly strong role of non-state actors in environmental governance. The case study focuses on the content of reforms, reasons why the non-state actor is so prominent, and the implications of policy reforms. State agencies face major challenges in environment-agriculture policy debates in places where environmental subsidies are unlikely, environmental information is poor, and organized private interests are influential.  相似文献   

Luminescence dating of ice‐marginal deposits in northern Germany: evidence for repeated glaciations during the Middle Pleistocene (MIS 12 to MIS 6)          下载免费PDF全文

Julia Roskosch  Jutta Winsemann  Ulrich Polom  Christian Brandes  Sumiko Tsukamoto  Axel Weitkamp  Werner A. Bartholomäus  Dierk Henningsen  Manfred Frechen 《Boreas: An International Journal of Quaternary Research》2015,44(1):103-126

The exact number, extent and chronology of the Middle Pleistocene Elsterian and Saalian glaciations in northern Central Europe are still controversial. This study presents new luminescence data from Middle Pleistocene ice‐marginal deposits in northern Germany, giving evidence for repeated glaciations during the Middle Pleistocene (MIS 12 to MIS 6). The study area is located in the Leine valley south of the North German Lowlands. The data set includes digital elevation models, high‐resolution shear wave seismic profiles, outcrop and borehole data integrated into a 3D subsurface model to reconstruct the bedrock relief surface. For numerical age determination, we performed luminescence dating on 12 ice‐marginal and two fluvial samples. Luminescence ages of ice‐marginal deposits point to at least two ice advances during MIS 12 and MIS 10 with ages ranging from 461±34 to 421±25 ka and from 376±27 to 337±21 ka. The bedrock relief model and different generations of striations indicate that the older ice advance came from the north and the younger one from the northeast. During rapid ice‐margin retreat, subglacial overdeepenings were filled with glaciolacustrine deposits, partly rich in re‐worked Tertiary lignite and amber. During MIS 8 and MIS 6, the study area may have been affected by two ice advances. Luminescence ages of glaciolacustrine delta deposits point to a deposition during MIS 8 or early MIS 6, and late MIS 6 (250±20 to 161±10 ka). The maximum extent of both the Elsterian (MIS 12 and MIS 10) and Saalian glaciations (MIS 8? and MIS 6) approximately reached the same position in the Leine valley and was probably controlled by the formation of deep proglacial lakes in front of the ice sheets, preventing a further southward advance.  相似文献   

Chemical and textural equilibration of garnet during amphibolite facies metamorphism: The influence of coupled dissolution–reprecipitation          下载免费PDF全文

Tim J Dempster  Julie La Piazza  Andrew G Taylor  Nicolas Beaudoin  Peter Chung 《Journal of Metamorphic Geology》2017,35(9):1111-1130

Metamorphic equilibration requires chemical communication between minerals and may be inhibited through sluggish volume diffusion and or slow rates of dissolution in a fluid phase. Relatively slow diffusion and the perceived robust nature of chemical growth zoning may preclude garnet porphyroblasts from readily participating in low‐temperature amphibolite facies metamorphic reactions. Garnet is widely assumed to be a reactant in staurolite‐isograd reactions, and the evidence for this has been assessed in the Late Proterozoic Dalradian pelitic schists of the Scottish Highlands. The 3D imaging of garnet porphyroblasts in staurolite‐bearing schists reveals a good crystal shape and little evidence of marginal dissolution; however, there is also lack of evidence for the involvement of either chlorite or chloritoid in the reaction. Staurolite forms directly adjacent to the garnet, and its nucleation is strongly associated with deformation of the muscovite‐rich fabrics around the porphyroblasts. “Cloudy” fluid inclusion‐rich garnet forms in both marginal and internal parts of the garnet porphyroblast and is linked both to the production of staurolite and to the introduction of abundant quartz inclusions within the garnet. Such cloudy garnet typically has a Mg‐rich, Mn‐poor composition and is interpreted to have formed during a coupled dissolution–reprecipitation process, triggered by a local influx of fluid. All garnet in the muscovite‐bearing schists present in this area is potentially reactive, irrespective of the garnet composition, but very few of the schists contain staurolite. The staurolite‐producing reaction appears to be substantially overstepped during the relatively high‐pressure Barrovian regional metamorphism reflecting the limited permeability of the schists in peak metamorphic conditions. Fluid influx and hence reaction progress appear to be strongly controlled by subtle differences in deformation history. The remaining garnet fails to achieve chemical equilibrium during the reaction creating distinctive patchy compositional zoning. Such zoning in metamorphic garnet created during coupled dissolution–reprecipitation reactions may be difficult to recognize in higher grade pelites due to subsequent diffusive re‐equilibration. Fundamental assumptions about metamorphic processes are questioned by the lack of chemical equilibrium during this reaction and the restricted permeability of the regional metamorphic pelitic schists. In addition, the partial loss of prograde chemical and textural information from the garnet porphyroblasts cautions against their routine use as a reliable monitor of metamorphic history. However, the partial re‐equilibration of the porphyroblasts during coupled dissolution–reprecipitation opens possibilities of mapping reaction progress in garnet as a means of assessing fluid access during peak metamorphic conditions.  相似文献   

Segmentation and kinematics of the North America‐Caribbean plate boundary offshore Hispaniola          下载免费PDF全文

Sylvie Leroy  Nadine Ellouz‐Zimmermann  Jordane Corbeau  Frédérique Rolandone  Bernard Mercier de Lépinay  Bertrand Meyer  Roberte Momplaisir  José‐Luis Granja Bruña  Anne Battani  Céline Baurion  Evgueni Burov  Valérie Clouard  Rémy Deschamps  Christian Gorini  Youri Hamon  Manfred Lafosse  Jottin Leonel  Laetitia Le Pourhiet  Pilar Llanes Estrada  Nicolas Loget  Francis Lucazeau  Daniel Pillot  Jeffrey Poort  Kevin R. Tankoo  José‐Luis Cuevas  José‐Fernando Alcaide  Claude Jean Poix  Alfonso Muñoz‐Martin  Serge Mitton  Yamil Rodriguez  Julien Schmitz  Leonardo Seeber  Andres Carbo‐Gorosabel  Santiago Muñoz 《地学学报》2015,27(6):467-478

We explored the submarine portions of the Enriquillo–Plantain Garden Fault zone (EPGFZ) and the Septentrional–Oriente Fault zone (SOFZ) along the Northern Caribbean plate boundary using high‐resolution multibeam echo‐sounding and shallow seismic reflection. The bathymetric data shed light on poorly documented or previously unknown submarine fault zones running over 200 km between Haiti and Jamaica (EPGFZ) and 300 km between the Dominican Republic and Cuba (SOFZ). The primary plate‐boundary structures are a series of strike‐slip fault segments associated with pressure ridges, restraining bends, step overs and dogleg offsets indicating very active tectonics. Several distinct segments 50–100 km long cut across pre‐existing structures inherited from former tectonic regimes or bypass recent morphologies formed under the current strike‐slip regime. Along the most recent trace of the SOFZ, we measured a strike‐slip offset of 16.5 km, which indicates steady activity for the past ~1.8 Ma if its current GPS‐derived motion of 9.8 ± 2 mm a^?1 has remained stable during the entire Quaternary.  相似文献   

The Satah Mountain and Baldface Mountain volcanic fields: Pleistocene hot spot volcanism in the Anahim Volcanic Belt,west-central British Columbia,Canada     

Christian Kuehn  Bernard Guest  James K. Russell  Jeff A. Benowitz 《Bulletin of Volcanology》2015,77(3):1-27

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The response in floodplain respiration of an alpine river to experimental inundation under different temperature regimes          下载免费PDF全文

Tatjana Simčič  Nataša Mori  Christian Hossli  Christopher T. Robinson  Michael Doering 《水文研究》2015,29(26):5438-5450

The respiratory potential [i.e. electron transport system activity (ETSA)] of soils and sediments from five floodplain habitats (channel, gravel, islands, riparian forest and grassland) of the Urbach River, Switzerland, and actual respiration rate (R) of the same samples exposed to experimental inundation were measured. Measurements were carried out at three incubation temperatures (4°C, 12°C and 20°C), and ETSA/R ratios (i.e. exploitation of the overall metabolic capacity) were investigated to better understand the effects of temperature and inundation on floodplain functional heterogeneity. Furthermore, ETSA/R ratios obtained during experimental inundation were compared with ETSA/R ratios from field measurements to investigate the exploitation in total metabolic potential at different conditions. Lowest ETSA and R were measured in samples from channel and gravel habitats, followed by those from islands. Substantially higher values were measured in soils from riparian forest and grassland. Both ETSA and R increased with increasing temperature in samples from all habitats, while the ETSA/R ratio decreased because of a rapid response in microbial community respiration to higher temperatures. The metabolic capacity exploitation (i.e. ETSA/R) during experimental inundation was lowest in predominantly terrestrial samples (riparian forest and grassland), indicating the weakest response to wetted conditions. Comparison of experimentally inundated and field conditions revealed that in rarely flooded soils, the metabolic capacity was less exploited during inundation than during non‐flooded conditions. The results suggest high sensitivity in floodplain respiration to changes in temperature and hydrological regime. ETSA/R ratios are considered good indicators of changes in metabolic activity of floodplain soils and sediments, and thus useful to estimate the impact of changes in hydrological regime or to evaluate success of floodplain restoration actions. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献