Masters Degrees (DG)

Permanent URI for this collection

http://hdl.handle.net/11070/630

Browse

Browsing Masters Degrees (DG) by Subject "Burial history"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Seismic stratigraphy and burial history for source and reservour prediction in the Luderitz basin, license blocks 2412B and 2413B, offshore Namibia
    (University of Namibia, 2020) Joseph, Reginalda
    The Lüderitz Basin is one of the four Namibia’s offshore basins on the western African passive margin that evolved during continental break-up and subsequent opening of the South Atlantic during the late Jurassic and Cretaceous. It is considered as a hydrocarbon frontier that is largely under-explored with only one well (2513/8-1) drilled since the wake of hydrocarbon exploration along the Namibian offshore in the 1990s. Selected lines of the GPN13 2D seismic dataset on blocks 2412B/2413B and well 2513/8-1 were used to predict lithofacies in the basin based on seismic stratigraphic interpretation. A Wheeler diagram was constructed to obtain better insight into the time relationships of the depositional systems, and their relationships to surfaces of non-deposition, condensation and erosion. In addition, two model well locations were selected in the basin, one on the shelf and the other at the base of slope. The Cretaceous and Tertiary succession was divided into 19 Seismic Intervals (SI) based on the recognition of 11 seismic stratigraphic surface. As no direct well tie calibration could be carried out the assigning of stratigraphic ages required comparison of the GPN13 lines with interpretations from neigbouring areas contained in previously studies. Lithofacies were predicted based on seismic facies, system tracts, and analogue interpretations presented in publications on studies of neighboring areas. The lithology model proposes the presence of several source, reservoir and seal rock units in both, the syn-rift and post-rift succesions of the study area. The modelled thermal history suggests that potential Lower Cretaceous source rocks may have generated petroleum only at locations of thick overburden, such as the base of slope location.
  • Thumbnail Image
    Item
    Structural evolution and burial history of the Dolphin Graben, Northern Walvis Basin (block 1911), offshore Namibia
    (University of Namibia, 2021) Thomas, Frieda Kahewa-Ketu; Wanke, Ansgar
    This research is on the structural evolution and burial history of the the Dolphin Graben. The Dolphin Graben is a prominent graben structure situated on the continental slope in the northern Walvis Basin, immediately south of the Walvis Ridge and the Phoenix Volcanic Field. The Dolphin Graben is under-explored with only two wells located in it. Minor oil shows are reportedfrom well1911/15-1, while well 1911110-1 is labelled as dry. At least two regional source rock intervals are predicted to be present in the graben, one in the Aptian-Albian, the other in the Cenomanian-Turonian. None of the two exploration wells penetrated the Albian-Aptian source rock. The intersected Cenomanian-Turonian source rocks at the two well sites in the graben are recognized to be immature. Thus, the questions on the presence of a mature source rocks, reservoir charge access and hydrocarbon preservation within the graben remained pending. The project aims at providing the following three studies for the Dolphin Graben: a (1) detailed structural evolution analysis, (2) reconstruction of the burial history in 1D at three locations, and a (3) re-assessment of the hydrocarbon potential of the Dolphin Graben taking into account the structural evolution and burial history models. Seismic interpretation was carried out in Petrel softvvare, while 1 D burial hi tory models were created with PetroMod software. Seismic interpretation formed the foundation of the structural evolution study; it entailed marker horizon mapping, fault mapping and subsequently fault displacements measurements. JD burial models were created for three locations, namely well1911110-1, wel/1911115-1 andfor a pseudo well herein labelled as "New well". Subsequent thermal and maturity models were created with calibration data from the two 1911 wells. 11 A regional and local structural model were created from seismic data. The regional model gives a concept of the wider deeper crustal structure of the northern Walvis Basin, while the local model is rather a reconstruction of phases of fault activity specific for the structures defining the Dolphin Graben. A main outcome of the study is that the Dolphin Graben is a rift system that is independent from the general Namibian margin syn-rift extension. The graben formed after deposition of the syn-rift sequence and Seawards Dipping Reflectors (SDRs). In fact, most of the graben subsidence occurred during the early passive margin drift phase. The graben development commenced during the Barremian or early Aptian and two main extensional phases (Extension phases I and II) are recognized. The mechanism for this local rift is not fully understood but could relate to local thermal mantle anomalies associated with the volcanism at the adjacent Phoenix Volcanic Field and Walvis Ridge. Predicted lacustrine source rocks deposited during early extension and they are likely confined to ponds in smaller half grabens. During progressive extension, the smaller grabens became inactive, while extension vvas accommodated by a few main .faults that outline the Dolphin Graben. A continuous marker horizon in the Dolphin Graben has similar seismic characteristics and is located at a similar stratigraphic level as the known Aptian Albian source rock in the southern Walvis Basin. Hence, this seismic marker is understood as an indication that the Aptian-Albian source rock is well-developed in the Dolphin Graben. There, it is essentially laterally extensive, but condensed or absent on central structural highs and on the graben flanks. Another distinct seismic horizon ties well to the Cenomanian Turonian source rock in the 1911 wells and it extends over the entire Dolphin Graben. The lll ID burial history and thermal models revealed maturity of older presumed lacustrine as well as for the Aptian-Albian source rocks. A minor oil show is reported in drilled Lower Cretaceous carbonates occurring on a structural high in the central graben. It is possible that hydrocarbons used extensional faults as migration pathways to charge those carbonates. The Cenomanian-Turonian source rock has been identified as immature to early mature. With I 0. 6 % TOC it is a potentially excellent source rock, but burial depth within the Dolphin Graben was essentially insLifjicient for hydrocarbon generation. Therefore, fitture exploration should focus on petroleum plays that concentrate on the Aptian-Albian source rocks