An approach to combined rock physics and seismic modelling of fluid substitution effects     

Tor Arne Johansen  Åsmund Drottning  Isabelle Lecomte  Håvar Gjøystdal 《Geophysical Prospecting》2002,50(2):119-137

The aim of seismic reservoir monitoring is to map the spatial and temporal distributions and contact interfaces of various hydrocarbon fluids and water within a reservoir rock. During the production of hydrocarbons, the fluids produced are generally displaced by an injection fluid. We discuss possible seismic effects which may occur when the pore volume contains two or more fluids. In particular, we investigate the effect of immiscible pore fluids, i.e. when the pore fluids occupy different parts of the pore volume. The modelling of seismic velocities is performed using a differential effective‐medium theory in which the various pore fluids are allowed to occupy the pore space in different ways. The P‐wave velocity is seen to depend strongly on the bulk modulus of the pore fluids in the most compliant (low aspect ratio) pores. Various scenarios of the microscopic fluid distribution across a gas–oil contact (GOC) zone have been designed, and the corresponding seismic properties modelled. Such GOC transition zones generally give diffuse reflection regions instead of the typical distinct GOC interface. Hence, such transition zones generally should be modelled by finite‐difference or finite‐element techniques. We have combined rock physics modelling and seismic modelling to simulate the seismic responses of some gas–oil zones, applying various fluid‐distribution models. The seismic responses may vary both in the reflection time, amplitude and phase characteristics. Our results indicate that when performing a reservoir monitoring experiment, erroneous conclusions about a GOC movement may be drawn if the microscopic fluid‐distribution effects are neglected.  相似文献   

Chironomids as quantitative indicators of mean July air temperature: validation by comparison with century-long meteorological records from northern Sweden   总被引：4，自引：0，他引：4  

Isabelle Larocque  Roland I. Hall 《Journal of Paleolimnology》2003,29(4):475-493

This study evaluates the potential of using chironomid assemblages to estimate past temperature changes by comparing chironomid-inferred temperatures to meteorological data for the last 87 years. This comparison is made using high-resolution (i.e., sub-decadally resolved) short cores of four lakes along a gradient of altitude (Lake Njulla, 999 m a.s.l., Lake 850, 850 m a.s.l., Lake Alanen Laanijavri, 365 m a.s.l. and Lake Vuoskkujavri, 348 m a.s.l.), vegetation (pine forest to alpine tundra vegetation) and temperature (mean July temperature of 12.4 to 8.1°C). Patterns of chironomid-inferred changes in mean July air temperature were highly comparable to changes in the meteorological data. Moreover, instrumental data were almost always within the specific errors of the quantitative estimates using chironomids. These results indicate that chironomids can be used as a powerful tool to reconstruct temperatures and that chironomids are sensitive enough to record temperature changes of low magnitude such as those recorded during the Holocene. Although this relationship between temperature and chironomid community is strong for the last 87 years, we cannot assume that other environmental factors such as organic matter, changes of lake water depth or oxygen availability were not more significant over longer temporal scales of the Holocene, or longer.  相似文献   

Long-term elasticity in the continental lithosphere; modelling the Aden Ridge propagation and the Anatolian extrusion process   总被引：4，自引：0，他引：4  

Aurélia Hubert-Ferrari  Geoffrey King  Isabelle Manighetti  Rolando Armijo  Bertrand Meyer  Paul Tapponnier 《Geophysical Journal International》2003,153(1):111-132

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Compartmentalisation of fluid migration pathways in the sub-Andean Zone, Bolivia     

Isabelle Moretti  Pierre Labaume  Simon M. F. Sheppard  Jacques Boulgue 《Tectonophysics》2002,348(1-3)

Numerous observations indicate that faults play a major role on the migration pathways of fluids in the Bolivian sub-Andean Zone. Most oil seeps in the foothills are located on faults, but oil fields in the foredeep are closed by faults. In the foothills, analysis of cements in fractures inside and around fault zones indicates that the faults act as barriers for transversal migration but can be preferential lateral migration pathways for both hydrocarbons and water. A detailed study of these apparent contradictions suggests that the hydraulic behaviour of faults changes with depth in relation with sandstone diagenesis, but it is strain-independent. From microstructural analyses of fault zones, we suggest that the main controlling factor is temperature, which facilitates or inhibits quartz precipitation. This result implies that the same fault is a barrier for lateral and transversal migration at depths >3 km, due to sealing of fractures by authigenic quartz at T>80 °C, and is a lateral drain in its shallower parts. As a result, the various thrust sheets are isolated from a hydraulic point of view, whereas migration in the foreland may take place over long distances (>100 km).  相似文献   

Thermal regime of fold and thrust belts—an application to the Bolivian sub Andean zone     

Laurent Husson  Isabelle Moretti 《Tectonophysics》2002,345(1-4)

A quantitative analysis of the various parameters influencing the thermal regime in orogenic belts and related foredeeps shows that (i) the increasing heat flow in internal zones is mainly due to the thickening of radiogenic layers, although there is no simple proportionality between crustal thickness and heat flow signal at large scale; (ii) in external zones, where the horizontal strain rate is large (such as in the Bolivian Andes), surface processes can be of first order within the first kilometers of the crust. Hence, they induce a large scatter in the thermal data which are acquired at shallow depths. The deep thermal regime can be restored only by a quantitative assessment of these parameters. Active erosion (respectively sedimentation) can increase (resp. reduce) the heat flow by a factor of 2 in the uppermost kilometers. The effects of fluid circulation percolating at depth can also generate significant local disturbances. Other processes such as heat advection during thrusting, surface morphology and climate change have a minor influence in most settings, compared to the aforesaid effects.In the Bolivian Sub Andean Zone, between 18°S and 22°S, the very active deformation enhances the surface thermal perturbations (particularly erosion and sedimentation) and disturb the thermal field. The analysis of these data accounting for the kinematics of the belt allows the lateral variations of the thermal regime at various scales to be assessed. A slight eastward increase in the thermal regime towards the Chaco plain is evidenced as well as towards the Boomerang area, as the Mesozoic and Cenozoic sedimentary cover gets thinner.  相似文献   

Computerized balanced cross-section LOCACE to reconstruct an allochthonous salt sheet, offshore Louisiana     

Isabelle Moretti  Shengyu Wu  Albert W. Bally 《Marine and Petroleum Geology》1990,7(4)

The evolution of an allochthonous salt sheet underlying the Mississippi fan is quantified using the two-dimensional LOCACE balanced section program. A first set of tests shows that the shape of the principal normal fault associated with the salt sheet is inconsistent with a roll-over geometry when using flexural slip or simple 120° linear shear criteria with a fixed footwall geometry. The next test with corrected fault geometry allows coherent restoration at the early Lower Miocene using the flexural slip criterion. In two-dimensional reconstructions, the area of salt cannot be balanced, i.e. the area available for salt is considerably wider than the actual salt area shown on the initial section. Thus either salt was dissolved or, perhaps more likely, salt moved outside the plane of section calling for a three-dimensional volumetric reconstruction procedure. The final interpretation is geometrically consistent and suggests that since early Lower Miocene time a large amount of salt moved out of the plane of section forming the allochthonous salt masses. An attempt to approximately balance salt volumes in three dimensions suggests that the amount of salt escaping the system is at least 18%.  相似文献   

An analysis of discards from the French trawler fleet in the Celtic Sea   总被引：2，自引：4，他引：2  

Rochet  Marie-Joelle; Peronnet  Isabelle; Trenkel  Verena M. 《ICES Journal of Marine Science》2002,59(3):538-552

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Cod egg characteristics and viability in relation to low temperature and maternal nutritional condition   总被引：2，自引：2，他引：2  

Ouellet  Patrick; Lambert  Yvan; Berube  Isabelle 《ICES Journal of Marine Science》2001,58(3):672-686

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Seasonal dynamics of Zostera noltii hornem. In the bay of arcachon (France)     

Isabelle Auby  Pierre-Jean Labourg 《Journal of Sea Research》1996,35(4):269-277

Seasonal dynamics of Zostera noltii was studied during 1984 in Arcachon Bay, France. In this Bay, Z. noltii colonizes 70 km², i.e. approximately 50% of the total area, while Z. marina occupies only 4 km². Densities and length of vegetative and generative shoots and above-ground and below-ground biomasses were monitored in four meadows which differed according to their location in the Bay, tidal level and sediment composition. Three of these meadows were homogeneous, well-established beds whilst the fourth was under colonization and patchy. Shoot densities and maximal below-ground biomass were lower in the inner silty seagrass bed than in the sandy meadows located in the centre of the Bay. Maximal above-ground biomasses were similar in the two population types. In the well-established beds, vegetative shoot densities, above-ground and below-ground biomasses showed a unimodal pattern with minima in winter (4000 to 9000 shoots·m⁻², 40 to 80 g DW·m⁻², and 40 to 60 g DW·m⁻², respectively) and maxima in summer (11000 to 22000 shoots·m⁻², 110 to 150 g DW·m⁻², and 140 to 200 g DW·m⁻², respectively). Reproductive shoots were observed from the beginning of June until the end of September, except in the colonizing bed where they persisted until December. Furthermore, in the latter, maximal reproductive shoot density was higher (2600 shoots·m⁻²) than in the established beds (650 to 960 shoots·m⁻²). The total production of Z. noltii in Arcachon Bay was estimated to approximately 35.6·10⁶ kg DW·y⁻¹ (19.4·10⁶ kg DW·y⁻¹ for above-ground parts and 16.2·10⁶ kg DW·y⁻¹ for below-ground parts).  相似文献   

Sub-pixel classification of SPOT-VEGETATION time series for the assessment of regional crop areas in Belgium   总被引：1，自引：0，他引：1  

Sara Verbeiren  Herman Eerens  Isabelle Piccard  Ides Bauwens  Jos Van Orshoven 《International Journal of Applied Earth Observation and Geoinformation》2008,10(4):486

Global time series of low resolution images are available with high repeat frequency and at low cost, but their analysis is hampered by the presence of mixed pixels and the difficulty in locating detailed spatial features. This study examined the potential of sub-pixel classification for regional crop area estimation using time series of monthly NDVI-composites of the 1 km resolution sensor SPOT-VEGETATION. Belgium was selected as test zone, because of the availability of ample reference data in the form of a vectorial GIS with the boundaries and cover type of the large majority of agricultural fields. Two different methods were investigated: the linear mixture model and neural networks. Both result in area fraction images (AFIs), which contain for each 1 km pixel the estimated area proportions occupied by the different cover types (crops or other land use). Both algorithms were trained with part of the reference data and validated with the remainder. Validation was repeated at three different levels: the 1 km pixel, the municipality and the agro-statistical district. In general, the neural network outperformed the linear mixture model. For the major classes (winter wheat, maize, forest) the obtained acreage estimates showed good agreement with the true values, especially when aggregated to the level of the municipality (R² ≈ 85%) or district (R² ≈ 95%). The method seems attractive for wide-scale, regional area estimation in data-poor countries.  相似文献