Добірка наукової літератури з теми "Barres de shoreface"

ABSTRACT The influence of tides on the sedimentology of wave-dominated shorefaces has been emphasized in recent studies of modern shorelines and related facies models, but few ancient examples have been reported to date. Herein, we use a case study from the stratigraphic record to develop a revised facies model and predictive spatio-temporal framework for high-energy, tidally modulated, wave-dominated, barred shorefaces. Kimmeridgian–Tithonian shallow-marine sandstones in the Weald Basin (southern England and northern France) occur as a series of laterally extensive tongues that are 5–24 m thick. Each tongue coarsens upward in its lower part and fines upward in its upper part. The lower part of each upward-coarsening succession consists of variably stacked, hummocky cross-stratified, very fine- to fine-grained sandstone beds and mudstone interbeds that are moderately to intensely bioturbated by a mixed Skolithos and Cruziana Ichnofacies. This lower part of the succession is interpreted to record deposition on the subtidal lower shoreface, between effective storm wave base and fairweather wave base. The upper part of each upward-coarsening succession comprises cross-bedded, medium- to coarse-grained sandstones that are pervasively intercalated with mudstone-draped, wave-rippled surfaces (including interference ripples) which mantle the erosional bases of trough cross-sets. Bioturbation is patchy, and constitutes a low-diversity Skolithos Ichnofacies. Cross-bedded sandstones are arranged into cosets superimposed on steeply dipping (up to 10°) clinoforms that dip offshore and alongshore, and extend through the succession. These deposits are interpreted to record shallow subtidal and intertidal bars on the upper shoreface, which likely contained laterally migrating rip channels or formed part of a spit. The lower, upward-coarsening part of each sandstone tongue represents an upward-shallowing, regressive shoreface succession in which the internal bedding of upper-shoreface sandstones was modulated by tidal changes in water depth. The upper, upward-fining part of each sandstone tongue typically comprises an erosionally based bioclastic lag overlain by subtidal lower-shoreface deposits, and constitutes an upward-deepening succession developed during transgression. Regressive–transgressive sandstone tongues fringe the northeastern margin of the basin, which was exposed to an energetic wave climate driven by westerly and southwesterly winds with a fetch of 200–600 km. The high tidal range interpreted from the shoreface sandstone tongues is attributed to resonant amplification in a broad (150–200 km), shallow (18–33 m) embayment as the tidal wave propagated from the Tethys Ocean into the adjacent intracratonic Laurasian Seaway, of which the Weald Basin was a part.

Abstract The morphology of wave-dominated clastic shorelines (i.e., foreshore and upper-shoreface sediments) can vary from barred to nonbarred, though the ancient record of nonbarred, sand-dominated shorelines has yet to be recognized. Here, a facies and quantitative architectural analysis of a clastic succession characterized by sandy inclined beds is presented and interpreted as the record of a high-gradient, nonbarred shoreline. Inclined beds dip seaward, have a tangential geometry (<3 m height, <40 m length, <11° dip), and are composed of planar lamination along the foresets and subordinate small-scale trough cross-bedding in the bottomsets. This facies distribution reflects a steep beach profile with a narrow surf zone and the development of plane beds both in foreshore and proximal upper-shoreface settings. Successive packages of inclined beds (a few tens of meters wide) are interpreted as the seaward accretion of this shoreline morphology, producing distinctive architectural elements (foresets and bottomsets). For the first time, we propose diagnostic criteria for identification in the rock record of the widely used modern nonbarred clastic shoreline model, and we contrast them with classical facies models of barred systems. Moreover, we discuss similarities and differences with radar-based Holocene coastal architectural elements, highlighting the need to incorporate detailed two-dimensional quantitative studies for refining the reconstruction of deep-time and recent clastic shorelines.

Well-constrained depositional models are essential for successful exploration and field development. The Skagen spitsystem offers a unique possibility for the establishment of a depositional model constrained by excellent outcrops, welldefined palaeogeography, good age control and detailed observations on hydrodynamics and morphology of the prograding part of the spit-system. The model offers a supplementary interpretation of shallow marine sandstones to the existing delta and linear shoreface models. The sand-dominated Skagen spit-system is c.22 km long, 4 km wide and up to 35 m thick, with a sand volume of c.2.2 km3. If filled with oil, this system would contain 0.6 km3 corresponding to 3.8 x 109 barrels assuming a porosity of 30% and an oil saturation of 90%. This is comparable in size with the largest Danish oil field (the Dan field), in the North Sea. Reservoir models for isolated linear ‘offshore’ sandstone bodies have been controversial for many years. Their size and internal indications of palaeocurrent directions are similar to those of the spit-system model, and this model may therefore be applicable for some of these bodies.

Abstract Burley Beach (southeastern Lake Huron) exhibits a multi-barred shoreface, the long-term equilibrium morphology characteristic of many low angle, sandy beaches in the Canadian Great Lakes. During a single major storm, a new bar emerged 50-60 m offshore as an irregular trough-crest form, through differential erosion of an existing shore terrace. Emergence, bar growth and offshore migration were associated with: (a) an overall negative sediment balance in the inner surf zone initially (‑2.30 m3>/m beach width), but with a large positive sediment balance (+5.10 m3/m) subsequent to the storm peak and during the storm decay; (b) progradation of the beach step to produce a new shore terrace; and (c) offshore migration of the two outer bars to provide the accommodation space necessary for the new bar. The primary transport mechanisms accounting for emergence of the new bar, its growth and migration were: (a) the mean cross-shore currents (undertow), which always transported suspended sediment offshore; and (b) the onshore transport of suspended sediment by incident gravity wave frequencies early in the storm and subsequently by infragravity waves (at the storm peak and the decay period). The longshore transport of sediment was significant in terms of the gross transport, although the net result was only a small transport to the south-west (historic littoral transport direction). It did not cause bar initiation, but it may have supplied some of the sediment for bar growth. The primary mechanism for bar initiation and growth was the cross-shore displacement of sediment by wave-driven (oscillatory) transport and cross-shore mean currents (undertow).

La morphologie et la structure interne du banc de sillage de la Horaine sont décrites à partir de donnéesobtenues par sondeur multifaisceaux et sismique réflexion haute résolution, couplées à des données de vibrocarottage et datations au radiocarbone. La structure interne du banc révèle 4 unités sismiques (U1-U4) sur un socle protérozoïque (U0). L'unité basale U1 est interprétée comme des sédiments fluviatiles de bas niveau marin remaniés pour remplir les micro-incisions du socle protérozoïque lors la transgression holocène. Cette unité est recouverte par l’unité U2, mise en place par dérive littorale à la manière des flèches sableuses, dans un contexte de remontée rapide du niveau marin. L'unité U3 progradante est interprétée comme des dépôts d'inondation marine en continuité avec l'unité U2. L'unité U4 est caractérisée par des réflecteurs obliques orientés dans 2 directions opposées. Cette dernière unité, datée entre 3800 et 3500 ans BP, correspond à des dunes migrantes surimposées au banc et observables également à partir des données bathymétriques. La forte corrélation entre les courants tidaux et la direction apparente de migration des dunes dans le sens horaire, suggère la présence d'un gyre tidal contrôlant la dynamique actuelle de la plupart des dunes associées au banc. Un comblement important de fond de baie par migration de barres sableuses (~100m/an), et régime de flux dispersif est observé grâce de l’imagerie satellitaire et photogrammétrie SfM par drone. Le recoupement avec l’analyse exploratoire des données climatiques ERA5 du programme Copernicus a permis de préciser qu’à moyen terme (échelle décennale), la migration des barres est contrôlée par la dynamique tidale (puissance hydraulique, temps d’immersion des barres) et à court terme (échelle saisonnière) le contrôle de la dynamique intertidale semble être assuré par la houle, et les tempêtes. Cette étude propose une nouvelle approche intégrée (mer-terre) pour le suivi de la dynamique de baie
The morphology and internal structure of the Horaine banner bank are described using multibeam and high- resolution seismic reflection data, coupled with vibro-coring and radiocarbon dating. The internal structure of the bank reveals 4 seismic units (U1-U4) on a proterozoic basement (U0). The basal unit U1 is interpreted as reworked lowstand fluvial sediments those infilled micro incised valleys during a rise in sea level. This unit is overlain by paleo-coastal barrier sand-spit (U2) whose development was controlled by swell in the context of a rapid rise in sea level. The successive prograding unit (U3) is interpreted as flooding deposits in continuity with unit U2. The unit U4 is characterized by oblique reflectors oriented in two opposite directions. This last unit, dated between 3800 and 3500 yr. BP, corresponds to migrating dunes superimposed on the bank and observable in the high-resolution bathymetric data. The strong correlation between tidal currents and the apparent clockwise migration of dune crests suggests the presence of a tidal gyre controlling the present- day dynamics of most of the Horaine bank dunes. A significant filling of the bay intern part by sand bar migration (100m/year on average), and dispersive flood regime is observed thanks to satellite imagery and UAV SfM photogrammetry. The cross-check with the exploratory analysis of the ERA5 climate data of the Copernicus program allowed to specify that in the medium term (decadal scale), the migration of the bars is controlled by the tidal dynamics (hydraulic power, immersion time of the bars) and in the short term (seasonal scale) the control of the intertidal dynamics seems to be ensured by the swell, and the storms. This study proposes a new integrated approach (sea-land) for monitoring bay dynamics

ABSTRACT An optimized completion design that addresses gaps in the existing single well Producer-Injector (P-I) concept is presented in this paper. Field development scenarios based on the optimized P-I concept and conventional waterflood were implemented in full-field 3D simulation models. Detailed review of the existing single P-I well concept revealed gaps in the completion design with regards to feasibility of data acquisition, ease of well intervention and well safety/control. The existing design utilizes a Single-String-Single (SSS) design with through-tubing water injection and oil production through annulus, whilst the optimized design is a Two-String-Dual (TSD) incorporating the flexibility of independent injection/production, zonal isolation for interventions & data acquisition and additional safety completion jewelries. A fit-for-purpose reservoir candidate was selected by assessing it's suitability to waterflooding. The reservoir belongs to the paralic sequence of the Agbada Formation of the Niger Delta basin – a sequence of interbedded sandstones and shales. The reservoir is an elongated anticline bounded by W-E oriented faults and exhibiting channelized shoreface sediments. Porosity and permeability ranges are 17-31% and 200mD-2200mD respectively. Shale baffles strongly reduces the influence of the aquifer hence the simulation model is an oil reservoir with weak aquifer completed by the P-I well producing oil and injecting into the aquifer in tandem. Performance of the single P-I well strategy was benchmarked against conventional waterflood patterns to effectively capture the recovery efficiency and production forecast for each scenario. Results from the five-parameter experimental design based on the P-I strategy, indicate Ultimate Oil Recovery is most impacted by horizontal permeability; injection rate, flow barrier transmissibility and vertical permeability with the least influence. Dynamic 3D water saturation maps show the waterflood front propagating principally in the horizontal direction from the injector, providing important reservoir boundary pressure support and minimizing the chance for injected water short-circuiting at the sandface. Ultimate Oil Recovery of 5spot/line drive patterns and the P-I strategy were similar, 54% and 52% respectively. Well completion costs and forecasts were fed into simple economics spreadsheet to test which technique provides the most value. Open book economics results showed the P-I concept provides better value (NPV 23.0 and VIR 0.67) than 5 spot and line drive patterns (NPV-17 and VIR-0.14).