>Magister Scientiae - MSc / The Sable Field constitutes a Basin Floor Channel (BFC) complex (E-BD reservoir) and a Basin Floor Fan (BFF) complex (E-CE reservoir). The reservoir sands were deposited during early-drift sedimentation in the Bredasdorp Basin. Paleo-current flows from the west, filling the basin with sediments that are eroded off the continental shelf (Agulhus Arch) and deposited on the base of the continental slope and basin floor. Turbidite flows off the Agulhus arch have deposited the Sable Fields reservoirs, where the larger channelized reservoir body takes an 80° bend off the continental slope and flows onto the basin floor. This 3-D reservoir highlights the reservoirs internal heterogeneity and complexity at the well bore and away from the well bore. Well tops tie wells to the 3-D seismic cube for; reservoir location and delineation, velocity modelling and subsequent conversion of the mapped surfaces from time to depth. Core and petro-physical analysis were used to outline the depositional facies within the investigated wells namely: E-BD5, E-BD2, E-BD1 and E-CE1. Correlation of depositional facies at the well bore with their corresponding seismic facies, allows for extrapolation of facies away from the well bore. The internal heterogeneity of the reservoir is outlined using an integrated methodology, which is based on log scale depositional features (channels, sheets, lobes) that are extrapolated to field scale (sand rich complex) using corresponding top and base reservoir seismic responses. The investigated thick region of sediment accumulation on: the continental slope, the base of the continental slope and basin floor is deposited on the 13AT1 early drift unconformity. The reservoir is outlined from the up-dip to the down-dip reaches of the field. Well E–BD5 has tapped into the proximal region (up-dip), with reservoir comprising of amalgamated channel sands that are deposited by laterally switching and stacking channelized sand bodies. Channel meander facies are seen in the upper portion of the reservoir, with massive channel fill in the lower parts. The channel fill constitutes a high net to gross with little to no lateral facies variations. This confined environment is dominated by amalgamated massive sands (on-axis) that are thinner bedded towards the banks of the channels (off-axis). A high degree of channel amalgamation has been interpreted in both up-dip wells E-BD5 and E-BD2. This channelized reservoir is at least 2km wide and 6km long, before the larger channel makes a rapid 80° change in paleo-current direction. This is possibly the result of basin floor topography and the stacking of previously deposited sand complexes which alter local sea floor topography. The vertical and lateral continuity of the channelised reservoir is generally excellent due to the high degree of channel amalgamation. The stacked channel complex constitutes a gross thickness of 76.2m (68.5m Net sand) in well E-BD5, and a gross thickness 25m (23m Net sand) in well E-BD2. Channel sands in well E-BD5 have an average porosity of 15% while the average porosity of channel sands in well E-BD2 (further down-dip) is 17%. This up-dip channelised region results in high amplitude reflections due to hydrocarbon charged sand juxtaposed against hemipelagic muds and silty levee facies. Well E-BD1 has tapped into a relatively confined sand complex deposited at the base of the continental slope. The amalgamated lobe and sheet sand complex is entirely encased in hemi pelagic mud. These reservoir sands are interpreted to be deposited in the Channel Lobe Transition Zone (CLTZ), thus the reservoir sands are interpreted to have a transitional depositional style (generally channelized sheets). The CLTZ region is thus dominated by both channel complex and lobe complex elements. The E-BD1 reservoir constitutes a number of amalgamated elements that result in a reservoir zone with an average porosity of 16.4%. These include: amalgamated thick bedded sheet sand (lobe axis) associated with deep depositional feeder channels; thin bedded sheet sands (off lobe axis), broad thin amalgamated lobe elements, layered thick bedded sand sheets and deep broad depositional channels. The low sinuosity broad depositional-channels and elongate lobe elements are expressed as lobate amalgamated sheets of sand which is up to 2-3km wide, 5km long and 30m thick (29.7m nett sand) at the well bore. Well E-CE1 has intersected 50m thick reservoir sand (50m nett sand) which constitutes the axis of a lobe complex where the reservoir zone has an average porosity of 14%. The sand rich complex is deposited on the unconfined basin floor. This reservoir complex constitutes amalgamated thick bedded lobe architectural elements which are massive in nature. The laterally continuous hydrocarbon charged lobe elements result in bright parallel seismic reflections. The amalgamated lobe complex is more than 5km wide. Sub-parallel horizons are attributed to the thin bedded off axis portion of the lobe complex where the net to gross is considerably less than the highly amalgamated axis of the lobe complex. The lobe complex has a moderate to good net to gross of 40-60%. The high aspect ratio of the lobe complex severely impacts the reservoirs vertical permeability, however horizontal permeability is quite good due to the extensive lateral continuity of good quality sheet sands. Based on the nature deep water architectural elements observed in this study, the internal heterogeneity of the Basin floor Fan and Basin floor channel complex’s may constitute an entire sand rich reservoir zone. All the sands may be in hydraulic communication if they are genetically related. These sands and stretch from the up-dip (wells E-BD5 & E-BD2) through to the transitional (E-BD2) and pinching out in the distal regions (E-CE1) on the basin floor. The seal constitutes a prominent shale horizon T13PW3 (8-10m thick) which is draped over the entire reservoir complex. This top seal is extrapolated from all the wells and correlated with seismic facies, thus outlining the lateral continuity and thickness variations of the top seal. This draped shale horizon exposes the thick axial portion of the amalgamated channel complex and amalgamated lobe complex.

The well-known clinoformal geometry of a basin-fill, with an alluvial to shelf segment, deep-water slope segment, and a basin floor segment, arises from the development of a wedge-shaped body of sediment at the basin-margin that has been termed a basin-margin wedge or a shelf-slope sedimentary prism. The basin-margin wedge characteristically has atopset-foreset clinoformal geometry, with its topset dominated by alluvial, coastal and shelfal processes, while its foreset is dominated by turbidite sedimentation. Tectonic configuration of the basin, sediment supply, and relative sea level variation are some of the major factors that control the development and growth of the basin-margin wedge. This dissertation documents two distinct stages of development of the basin-margin wedge at an Eocene active margin, and relates the observed variability in the nature of the shelf-margin, deep-water slope, and basin-floor deposits with these stages. The Tyee Basin in western Oregon was a forearc basin that was filled during late early Eocene and Middle Eocene under greenhouse climatic condition. The sedimentary succession of the Tyee Basin include continental, shallow-marine and deep-water sandstones that are well exposed in Coast Range area of Oregon. The variability observed within the thick and laterally extensive turbidite sandstones of the Tyee Basin led to contrasting depositional models for the Tyee basin in the past. Notably, the submarine ramp model, which provides an alternative model for deepwater coarse clastic deposition, was proposed based on the sedimentary succession of the Tyee Basin. Reconstruction of the clinoformal geometry of the Tyee Basin succession from detailed field data (more than 1000 outcrop locations) and subsurface data reveals two distinct stages of development of this active basin-margin. Each stage has a distinct style of clinoform development and a distinct character of associated sandy deepwater deposits. At the initial stage the basin-margin clinoforms appear to be small (< 250m clinoform height) and strongly progradational, with clinoform topset dominated by the feeder fluvial deposits. At this stage, sandy unconfined (not channelized) turbidite deposits accumulated on the Tyee deepwater slope and extended to the Tyee basin-floor. Large scale sediment conduits on the deepwater slope, in the form of slope channels or canyons, are notably absent in this stage. The second stage is characterized by larger clinoform height (> 500m), higher degree of topset aggradation with repeated fluvio-deltaic cycles on the shelf, and spectacular, sand-rich, well-organized turbidite channels and canyons on the slope. The slope channels active at this stage supplied coarse sediments to the basin-floor to form unusually thick basin-floor fans. The first infill stage represents the embryonic development of a basin-margin wedge on the Tyee continental margin, and could have some similarity with the previously mentioned submarine ramp model. But this was followed by a much longer period of basin-filling when repeated fluvial and shallow-marine cycles formed on the shelf and well-organized turbidite channels were active on the slope supplying sands to the Tyee Basin floor fans. It was concluded that the two stages of development of the basin-margin wedge in the Tyee Basin is controlled largely by the configuration of the basin, that is a result of the prominent topographic/bathymetric features in oceanic basement underlying the sedimentary succession of the Tyee Basin. Tectonically active hinterland and greenhouse climate may have contributed to a relatively high sediment supply to the basin. The relatively small-amplitude sea level variations expected under greenhouse climatic condition of the Early to Middle Eocene are likely to have relatively minor effect on the architecture of the basin-fill. The present work on Tyee Basin builds on earlier research on this basin, but now establishes a ground trothed clinoformal growth model, revises the existing interpretation of sediment transport direction during a major part of the basin-filling history, and demonstrates a two-stage evolution of margin accretion. The observations from the active Tyee Basin was compared and contrasted with a latest Pleistocene sediment wedge on the New Jersey outer shelf. This sediment wedge, developed under icehouse climatic condition, and on a passive margin, was studied using high resolution seismic data (CHIRP). In contrast to the sedimentary succession of the Tyee Basin, the depositional architecture of the sediment wedge on outer New Jersey shelf, which was interpreted as a set of falling stage deltaic clinothems, appears to be strongly controlled by eustatic sea level variation of latest Pleistocene. / text

This research investigates the character and significance of shelf-edge deltas within the sedimentary source-to-sink system, and how variability at the shelf edge leads to different styles of deep-water deposition. Because the shelf-edge represents one of the key entry points for terrigenous sediment to be delivered into the deep water, understanding of the sedimentary processes in operation at these locations, and the character of sediment transported through these deltas is critical to understanding of deep-water sedimentary systems. The research was carried out using three datasets: an outcrop dataset of 6000 m of measured sections from the Permian-Triassic Karoo Basin, South Africa, a 3D seismic data volume from the Eocene Northern Santos Basin, offshore Brazil and a dataset of 29 previously published descriptions of shelf-edge deltas from a variety of locations and data types. The data presented highlight the importance of sediment instability in the progradation of basin margins, and deep-water transport of sediment. The strata of the Karoo Basin shelf margin represent river-dominated delta deposits that become more deformed as the shelf-edge position is approached. At the shelf edge, basinward dipping, offlapping packages of soft-sediment-deformed and undeformed strata record repetitive collapse and re-establishment of shelf-edge mouth bar packages. The offlapping strata of the Karoo outcrops record progradation of the shelf margin through accretion of the shelf-edge delta, for over 1 km before subsequent transgression. The Eocene Northern Santos Basin shelf margin, in contrast, exhibits instability features which remove kilometers-wide wedges of the outer shelf that are transported to the basin floor to be deposited as mass-transport packages. In this example, shelf-edge progradation is achieved through „stable. accretion of mixed turbidites and contourites. The data also emphasize the importance of the role of shelf-edge delta processes in the delivery of sediment to the basin floor. A global dataset of 29 examples of shelf-edge systems strongly indicates that river domination of the shelf-edge system (as read from cores, well logs or isopach maps) serves as a more reliable predictor of deep-water sediment delivery and deposition than relative sea level fall as traditionally read in shelf-edge trajectories or sequence boundaries. / text