>Magister Scientiae - MSc / This study is located within the Bredasdorp Basin which is on the southern continental margin, offshore South Africa. The basin is located between Infanta and Agulhas arches and is a rift basin that is southeastern trending. Sedimentology reports have shown that the basin is predominantly filled by Aptian to Maastrichtian deposits which overlays pre-existing late Jurassic to Early Cretaceous fluvial and shallow marine syn-rift deposits. Devonian Bokkeveld Group slates and or Ordovician-Silurian Table Mountain Group quartzites are shown to be the composition of basement rocks. The study area incorporates only three wells for this research; well F-AH1, F-AH2 and F-AR1. This paper was completed through analyzing and juxtaposing interpretations of results from gamma ray wireline log analysis with core analysis in which these correlations and figures were displayed using Petrel software and Coral Draw respectively. Core analysis resulted in the identification of, sixteen litho-facies for the entire study, which were recognized according to its grain size, texture, sedimentary structures, colour changes, base and top contacts, bioturbation, noticeable minerals, etc. Facies tend to alternate all the way through each well and between different wells with similar facies being present in different wells, but they are not evident in all the cores. Based on the classification of sand bodies, core analysis provides good indication that the general depositional environment of reservoirs within the studied wells are within a marginal marine depositional environment which are tidally influenced. Log signatures typical of sandstone reservoir bodies were discovered in the field where sand bodies are 20 m thick or less and were recognized in the study area. Depositional environments were characterized based on depositional environment similarities: a funnel-shaped facies representing a crevasse splay; a cylindrical-shaped facies representing slope channel-fills representing the transgressive-regressive shallow marine shelf.

>Magister Scientiae - MSc / The area of concentration of this particular project is focused on the central part of the Bredasdorp Basin, block 9, offshore South Africa. Petrophysical evaluation of sandstone reservoirs of the F-0 tract offshore South Africa has been performed. The main aim of this study is to investigate the reservoir potential of this tract, using processed data of four wells which include; F-01, F-02, F-R1 and F-Sl. The data used for this evaluation include; wireline logs, conventional core data and special core analysis data (SCAL). Combining these laboratory results with wireline log examinations and core descriptions gives an idea of the sedimentary environment, sandstone properties and ultimately generates an effective model. Six facies were identified from the core, based on the grain size (facies 1, 2, 3, 4, 5 and 6). Facies 1 and 2 had the best reservoir rock qualities, whereas facies 3 to 6 are classified as poor or non - reservoir rock. These reservoirs are deposited in a shallow marine environment. Porosity and permeability are the two main properties which ultimately determine the quality of the reservoir. These two property measurements were taken from the routine core analysis and SCAL data and generated for the entire well using various methods. The Steiber equation was used to calculate the volume of clay from the gamma ray log. The average porosity for all four wells range between 0.5% to 17%. The minimum value recorded for permeability is 0.009mD and the maximum value is 235mD, even though permeability seems to have a broad range, the majority of the values recorded is less than lOmD. Based on these values, the reservoir rock properties are generally classified as moderate to fair. In some places, where the permeability is more than 100mD, the reservoir is classified as very good. Capillary pressure and conventional core data was compared to the log calculated water saturation models. The best fit model was the Indonesia model. The average water saturations range from 10% to 88 %. A total of eleven reservoir intervals were identified from the four wells based on the cut - off parameters. For an interval to be classified as a reservoir interval, the porosity should be equal or greater than 6%, water saturation equal or less than 35% and the volume of clay should be equal to or less than 40%. From the eleven intervals identified, four intervals contain gas and the remainder of the intervals identified are water bearing. The gross thickness of the reservoir ranges from 10m to 66m and net pay interval from 0.46m to 51.6m.

>Magister Scientiae - MSc / This study describes porosity and permeability distribution in the deep marine play of the central Bredasdorp Basin, Block 9, offshore South Africa using methods that include thin section petrography, X-ray diffraction, and scanning electron microscopy, in order to characterize their porosity and permeability distributions, cementation and clay types that affect the porosity and permeability distribution. The study includes core samples from nine wells taken from selected depths within the Basin. Seventy three thin sections were described using parameters such as grain size measurement, quantification of porosity and permeability, mineralogy, sorting, grain shape, matrix, cementation, and clay content. Core samples were analyzed using x-ray diffraction for qualitative clay mineralogy and phase analysis. Scanning electron microscope analysis for qualitative assessment of clays and cements. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses were conducted on fifty-four (54) and thirty-five (35) samples respectively to identify and quantify the clay mineralogy of the sandstones. The SEM micrographs are also useful for estimating the type and distribution of porosity and cements. Analyses of these methods is used in describing the reservoir quality. Detrital matrix varies in abundance from one well to another. The matrix consists predominantly of clay minerals with lesser amounts of detrital cements. X-ray diffraction analyses suggest these clays largely consist of illitic and kaolinite, with minor amounts of chlorite and laumontite. Because these clays are highly illitic, the matrix could exhibit significant swelling if exposed to fresh sea water, thus further reducing the reservoir quality. The majority of the samples generally have significant cements; in particular quartz cement occurs abundantly in most samples. The high silica cement is possibly caused by the high number of nucleation sites owing to the relatively high abundance of detrital quartz. Carbonate cement, particularly siderite and calcite, occurs in variable amounts in most samples but generally has little effect on reservoir quality in the majority of samples. Authigenic, pore-filling kaolinite occurs in several samples and is probably related. to feldspar/glauconite alteration, it degrades reservoir quality. The presence of chlorite locally (plate 4.66A & B) and in minute quantities is attributed to a late stage replacement of lithic grains. Don't put references to plates and figures in abstract. A high argillaceous content is directly responsible for the low permeability obtained in the core analysis. Pervasive calcite and silica cementation are the main cause of porosity and permeability destruction. Dissolution of pore filling intergranular clays may result in the formation of micro porosity and interconnected secondary porosity. Based on the combination of information derived from thin section petrography, SEM and XRD, diagenetic stages and event sequences are established for the sandstone in the studied area. Reservoir quality deteriorates with depth, as cementation, grain coating and pore infilling authigenic chlorite, illite and kaolinite becomes more abundant.

Magister Scientiae - MSc / Pressure drop within a field can be attributed to several factors. Pressure drop occurs when fractional forces cause resistance to flowing fluid through a porous medium. In this thesis, the sciences of petrophysics and rock physics were employed to develop understanding of the physical processes that occurs in reservoirs. This study focussed on the physical properties of rock and fluid in order to provide understanding of the system and the mechanism controlling its behaviour. The change in production capacity of wells E-M 1, 2, 3, 4&5 prompted further research to find out why the there will be pressure drop from the suits of wells and which well was contributing to the drop in production pressure. The E-M wells are located in the Bredasdorp Basin and the reservoirs have trapping mechanisms of stratigraphical and structural systems in a moderate to good quality turbidite channel sandstone. The basin is predominantly an elongated north-west and south-east inherited channel from the synrift sub basin and was open to relatively free marine circulation. By the southwest the basin is enclose by southern Outeniqua basin and the Indian oceans. Sedimentation into the Bredasdorp basin thus occurred predominantly down the axis of the basin with main input direction from the west. Five wells were studied E-M1, E-M2, E-M3, E-M4, and E-M5 to identify which well is susceptible to flow within this group. Setting criteria for discriminator the result generated four well as meeting the criteria except for E-M1. The failure of E-M1 reservoir well interval was in consonant with result showed by evaluation from the log, pressure and rock physics analyses for E-M1.iv Various methods in rock physics were used to identify sediments and their conditions and by applying inverse modelling (elastic impedance) the interval properties were better reflected. Also elastic impedance proved to be an economical and quicker method in describing the lithology and depositional environment in the absence of seismic trace.