المؤلفون: Lasisi, Ayodele Oluwatoyin

مرشدي الرسالة: Chatterjee, Tapas K.

مصطلحات موضوعية: Early cretaceous, Gamtoos basin, South Africa, Seismic facies, Formation evaluation

الوصف: Philosophiae Doctor - PhD
Integrated approaches in the study of petroleum exploration are increasingly becoming significant in recent times and have yielded much better result as oil exploration is a combination of different related topics. The production capacity in hydrocarbon exploration has been the major concern for oil and gas industries. In the present work an integrated approach was made with seismic, well logs and biostratigraphy for predicting the depositional environment and to understand the heterogeneity within the reservoirs belonging to Valanginian (Early Cretaceous) age of Gamtoos Basin, Offshore South Africa. Objectively, the integrated work was mainly based on seismic stratigraphy (seismic sequence and seismic facie analysis) for interpretation of the depositional environments with combination of microfossil biostratigraphic inputs. The biostratigraphic study provides evidences of paleo depth from benthic foraminifera and information about bottom condition within the sedimentary basin, changing of depositional depth during gradual basinal fill during the Valanginian time. The petrophysical characterization of the reservoir succession was based on formation evaluation studies using well logs to investigate the hydrocarbon potential of the reservoir across Valanginian depositional sequence. Further, the static modeling from 2D-seismic data interpreted to a geological map to 3D-numerical modeling by stochastic model to quantify the evaluation of uncertainty for accurate characterisation of the reservoir sandstones and to provide better understanding of the spatial distribution of the discrete and continuous Petrophysical properties within the study area.

الإتاحة: http://hdl.handle.net/11394/7075Test

المؤلفون: Hashim, Muazzam Ali

مرشدي الرسالة: Opuwari, Mimonitu

مصطلحات موضوعية: Heterogeneity, Velocity modelling, Interval velocities, Acoustic impedance, Seismic facies

الوصف: Magister Scientiae - MSc
Velocity modelling forms an integral part of the seismic interpretation process initially completed in two-way time. In order for a representative depth conversion, it is obligatory to construct a velocity model that serves the bridge between velocity and respective two-way time. This study deals with the investigation of subsurface heterogeneities and its impact on the variation of velocities. Interpretation of time domain reflection data results in one or more seismic horizons, however these horizons should represent the variation in subsurface geology as a result of acoustically different layers displaying varying reflection amplitudes. The purpose of this study was fulfilled by examining the variation of these velocities in relation to the geology and its significance towards building a velocity model. It is evident that complexities, such as an existing heterogeneous subsurface is present in the study area. Using velocities only considered at formation well tops, as a result, does not completely honour the variation in these velocities. The velocity profile as calculated from the sonic log was characterized into zones representing unique velocity trends. The analyses to understand the impact of subsurface heterogeneities on the velocities was completed by the application of seismic facies analysis which entailed the study of the seismic reflector patterns and amplitudes; a study of the lithologies present and the generation of mineral plots using available wireline logs, all of which in close relation to the variation in velocities. The characterized zones, as a result have shown that shaly sediments are typically associated with higher velocities (~2800 – 4600m/s) compared to sandstones of lower densities. Mineral plots however, have also indicated that where quartz minerals were present (specifically zone L), sandstones as a result have shown higher velocities (~4800m/s) as compared to the shales (~3600m/s). These higher velocities are also associated with more organised seismic reflectors with brighter amplitudes and strong contrasts in acoustic impedance as shown by the seismic. Uniform velocities were observed in zones such as zone Ia, typically associated with a low acoustic impedance contrast and minimal variation in its lithological make-up. The integrated investigation of subsurface heterogeneities has shown that velocities vary to a substantial degree as a result of existing subsurface heterogeneities. The variation of these velocities are hence significant enough that it should be considered when constructing a velocity model which aims to respect the geology of the study area. The result of understanding the relation between the geology and resultant velocities may prove to advance the results of the velocity model in a manner that it is more complete and representative of the subsurface.

الإتاحة: http://hdl.handle.net/11394/5328Test