L’utilisation de modeles photogrammetriques dans l’industrie
(surveillance des infrastructures, reseau de pipelines) et
l’archeologie (le releve topographique et la modelisation des sites)
s’est fortement developpee. En geologie, la methode a ete adaptee
pour imager les affleurements, souvent des falaises. L’acquisition
par un multicoptere, avec une camera orientable a permis d’obtenir
une modelisation photogrammetrique 3D de haute resolution
(quelques centimetres) sur des fronts verticaux prealablement
reperes (affleurements, falaises, glissements, failles). La resolution
peut varier en fonction des parametres d’acquisition (distance de
prise de vue). La repetition de cette methode dans le temps permet
de mesurer l’evolution de certains processus (erosion, depots
gravitaires, fronts de carriere).
Le logiciel d’interpretation developpe par l’IFPEN (Virtuoso) est
capable de gerer des fichiers 3D tuiles incluant plusieurs niveaux
de details (25 Gbits par site) : une resolution plus grande est affichee
en cas de zoom sur l’objet. Il permet d’effectuer le pointe
des horizons ou des failles, de mesurer des pendages, des angles,
des vecteurs ainsi que de construire des logs synthetiques dans
des zones difficiles d’acces. L’objectif principal est de restituer
la geometrie des corps sedimentaires. Les donnees sont calibrees
par des observations conventionnelles de terrain localisees a des
points clefs, elles sont etendues dans l’espace grâce au modele 3D
et l’ensemble s’integre dans les geomodeleurs classiques.
Nous presenterons deux interpretations de modele 3D. Dans le
Golfe de Corinthe, une zone de 8x3km a ete couverte par une
acquisition de 6000 photographies aeriennes (30 vols), le modele
3D obtenu permet de contraindre les architectures et les relations
des differents objets (delta, chenaux, levees, ” sediments waves
”, et lobes). Dans les series permiennes de Canyon Lands Park
(Utah ), une zone de 1x3km a ete modelisee (5000 photos, 18
vols 10km de falaise) dans un environnement mixte constitue de
barres de chenaux fluviatiles, de derives littorales et eoliennes. Le
modele permet d’apprehender la geometrie des barres greseuses
et les passages lateraux de facies.
L’interpretation des modeles facilite l’integration des donnees terrains
dans un modele geologique precis. Ces resultats servent
d’analogues a l’echelle du reservoir. La visualisation 3D favorise
le partage de ces resultats, et peut servir de support original educatif.
Abstract The architecture of lacustrine systems is the result of the complex interaction between tectonics, climate and environmental parameters, and constitute the main forcing parameters on the lake dynamics. Field analogue studies have been performed to better assess such interactions, and their impact on the facies distribution and the stratigraphic architecture of lacustrine systems. The Yacoraite Formation (Late Cretaceous/Early Palaeocene), deposited during the sag phase of the Salta rift basin in Argentina, is exposed in world‐class outcrops that allowed the dynamics of this lacustrine system to be studied through facies analysis and stratigraphic evolution. On the scale of the Alemania‐Metán‐El Rey Basin, the Yacoraite Formation is organized with a siliciclastic‐dominated margin to the west, and a carbonate‐dominated margin to the east. The Yacoraite can be subdivided into four main ‘mid‐term’ sequences and further subdivided into ‘short‐term’ sequences recording high frequency climate fluctuations. Furthermore, the depositional profiles and identified system tracts have been grouped into two end‐members at basin scale: (a) a balanced ‘perennial’ depositional system for the lower part of the Yacoraite Formation and (b) a highly alternating ‘ephemeral’ depositional system for the upper part of the Yacoraite Formation. The transition from a perennial system to an ephemeral system indicates a change in the sedimentary dynamics of the basin, which was probably linked with the Cretaceous/Tertiary boundary that induced a temporary shutdown of carbonate production and an increase in siliciclastic supply.
Abstract Deglacial sedimentary sequences recording the decay and final demise of ice sheets result from intricate interactions between the pattern of ice margin retreat, inherited basin physiography and relative sea-level (RSL) changes. A specific emphasis is here given to the glacio-isostatic adjustment (GIA), which may force postglacial local RSL fall in spite of concomitant glacio-eustatic rise. In this contribution, we characterize a Quaternary deglacial succession emplaced in such a setting, subsequently used as an analogue to interpret an end-Ordovician deglacial record. The Quaternary deglacial succession, tens of metres thick, formed under condition of RSL fall forced by the GIA in c. 10 000 years in the aftermath of the deglaciation. This sedimentary succession consists of a lower, fining-upward sequence representing the backstepping of ice-contact depocentres following the retreat of the ice margin, and an upper, coarsening-upward sequence that relates to the subsequent progradation of a glaciofluvial delta system. A very similar stratigraphic stacking pattern characterizes the Ordovician analogue, suggesting a comparable deglacial sequence. By analogy with the Quaternary succession, this ancient deglacial record would have hence been emplaced under conditions of RSL fall forced by the GIA. Moreover, it must only represent a very short time interval that could be viewed as virtually instantaneous regarding the Late Ordovician glaciation. Such a vision is at odds with commonly accepted interpretations for such successions.
Abstract On the Island of Samos (East Aegean region, Greece), two sedimentary basins are filled by thick continental series dated to the Late Miocene to Early Pliocene. A multidisciplinary study has been performed including (1) the definition of 21 sedimentary facies, (2) a review of the biological components and (3) carbon, oxygen and strontium stable isotope analyses. The succession is characterised by various depositional settings and hydrochemical compositions. Five main stages of basin evolution have been identified: (1) The Late Serravallian is marked by the development of alluvial fans and fan delta; (2) during the Lower Tortonian, isolated shallow lakes with variable salinity, from fresh to brackish, developed under warm and relatively humid conditions; (3) the Middle to Upper Tortonian is marked by the development of a large and deep lake with saline and alkaline waters, under colder and drier conditions; (4) the Latest Tortonian to Messinian period is represented by an ephemeral alluvial system, developed under a dry climate; (5) during the Zanclean, a palustrine and paludal wetland system, dominated by tufa carbonates, developed under moderately humid conditions. This succession is of particular interest for the reconstruction of the palaeoenvironmental evolution of the transition zone between the Mediterranean domain, and the Paratethys and circum‐Paratethys areas. The geochemical data and the presence of flora (diatoms) and fauna (gastropods) of marine affinity suggest transient ingressions of marine‐related water or groundwater inflows as early as the Lower Tortonian. The Samos succession records the complex interaction between the regional geodynamics and climate. The extensional regime of the Eastern Aegean zone generates subsidence, interrupted in the mid‐Tortonian (9 Ma) by a brief compressive event and a major exposure of the basins. Furthermore, the Late Miocene progressive aridification, followed by a change to a more humid climate (Pliocene) is also a major driver of the sedimentation.
Abstract Deglacial sequences typically include backstepping grounding zone wedges and prevailing glaciomarine depositional facies. However, in coastal domains, deglacial sequences are dominated by depositional systems ranging from turbiditic to fluvial facies. Such deglacial sequences are strongly impacted by glacio‐isostatic rebound, the rate and amplitude of which commonly outpaces those of post‐glacial eustatic sea‐level rise. This results in a sustained relative sea‐level fall covering the entire depositional time interval. This paper examines a Late Quaternary, forced regressive, deglacial sequence located on the North Shore of the St. Lawrence Estuary (Portneuf Peninsula, Québec, Canada) and aims to decipher the main controls that governed its stratigraphic architecture. The forced regressive deglacial sequence forms a thick (>100 m) and extensive (>100 km 2 ) multiphased deltaic complex emplaced after the retreat of the Laurentide Ice Sheet margin from the study area ca 12 500 years ago. The sedimentary succession is composed of ice‐contact, glaciomarine, turbiditic, deltaic, fluvial and coastal depositional units. A four‐stage development is recognized: (i) an early ice‐contact stage (esker, glaciomarine mud and outwash fan); (ii) an in‐valley progradational stage (fjord head or moraine‐dammed lacustrine deltas) fed by glacigenics; (iii) an open‐coast deltaic progradation, when proglacial depositional systems expanded beyond the valley outlets and merged together; and (iv) a final stage of river entrenchment and shallow marine reworking that affected the previously emplaced deltaic complex. Most of the sedimentary volume (10 to 15 km 3 ) was emplaced during the three‐first stages over a ca 2 kyr interval. In spite of sustained high rates of relative sea‐level fall (50 to 30 mm·year −1 ), delta plain accretion occurred up to the end of the proglacial open‐coast progradational stage. River entrenchment only occurred later, after a significant decrease in the relative sea‐level fall rates (<30 mm·year −1 ), and was concurrent with the formation and preservation of extensive coastal deposits (raised beaches, spit platform and barrier sands). The turnaround from delta plain accretion to river entrenchment and coastal erosion is interpreted to be a consequence of the retreat of the ice margin from the river drainage basins that led to the drastic drop of sediment supply and the abrupt decrease in progradation rates. The main internal stratigraphic discontinuity within the forced regressive deglacial sequence does not reflect changes in relative sea‐level variations.
The objectives of this work is to assess the impact of reservoir heterogeneities on heavy oil recovery of a reservoir analogue of meander belt through the Steam Assisted Gravity Drainage (SAGD) process by using numerical models. These models are obtained with different scales of upscaling of the geological model. Meander belts consist of point bar deposits, characterized by a 3D complex internal architecture, with different scales of heterogeneities, which distribution is associated with the depositional processes. Based on a 3D outcrop description of a meander belt analogue to the Canadian heavy-oil fields, the approach includes three steps: 1) the construction of a reference static reservoir model based on a very fine description of the outcrops in terms of architecture and geological heterogeneities, 2) upscaling of the grid at different scales using different upscaling factors in order to evaluate their impact on the heterogeneity distribution in the reservoir, 3) reservoir SAGD simulations using horizontal well doublet (steam injector and producer) across the meander belt, so as to assess the impact of upscaling of heterogeneities on heavy oil production. The impact of heterogeneities on simulation results are evaluated for several upscaling stages. Results show that heterogeneity distribution has an impact on fluid flow at different stages of production. On the fine gridded model, small scale heterogeneities impact the steam chamber development and fluid flow in the wellbore vicinity at the beginning of the steam injection, whereas large scale heterogeneities strongly influence oil recovery during the whole recovery process and lower the efficiency of the reservoir drainage. On coarser grids, the effect of small-scale heterogeneities can be diminished, depending on the upscaling stage. The geomechanical effect is not taken into account in this work, the objective being to assess the impact of heterogeneities on oil recovery. The performance of SAGD is clearly linked to the steam chamber development, which depends on the degree of heterogeneities present in the reservoir. The simulation workflow and the sensitivity study on the upscaling method contribute to a better restoration of the heterogeneity distribution in the reservoir. The negative effect of these heterogeneities during the oil recovery must thus be quantified in order to monitor the thermal production at crucial periods of the production process.
