Browsing by Author "Ojok, Tonny"

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    Analogue sandbox scaled modelling of oblique and orthogonal extension rifting in Rukwa rift basin, Tanzania
    (University of Dar es Salaam, 2021) Ojok, Tonny; Duot, John BK; Namaganda, Majorine; Sadiki, Nasra; Msabi, Michael
    Fault evolution in oblique and orthogonal rift systems in the brittle upper crust of the Rukwa rift basin was simulated using scaled sandbox modelling by varying the angle between the rift axis and the extension direction, α, through 45° and 90°, over a 10 cm displacement. The 45° oblique model exhibits a half-graben architecture bounded by a planar fault, intra-rift faults and a conjugate fault in some vertical sections. The map view of the model’s basin trends in the NW-SE direction, and is comparable with the Rukwa rift basin orientation. The 90° oblique model forms a basin structure which is orthogonal to the extension direction of the model in aerial photos. Its linear fault remains orthogonal to the extension direction, while the flexural side of the model segments into sinuous normal faults. Planar to slightly curved intra-rift faults are observed in vertical sections. The half-grabens have similar geometries in vertical sections for both models, while intra-rift faults elongate in vertical sections. The results of the oblique model are similar to natural examples of rift fault systems like the Rukwa rift. The fault geometries of the sandbox models can serve as examples for recognizing fault styles in oblique rift systems.
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    Petrophysical analysis of the red sandstone group of The Rukwa Graben, Southwestern Tanzania
    (The University of Dodma, 2021) Ojok, Tonny
    The study of various well-logs aids in the identification of potential sand and reservoir zones and their thicknesses within a formation. The current study addressed the lack of research and literature on the petrophysical properties and reservoir potential of the Red Sandstone Group (RSG) Formation in the Rukwa Basin, southwestern Tanzania. This study presents the findings of the petrophysical analysis of the RSG Formation in the Rukwa Rift Basin. The Techlog computer program was used to analyse the Ivuna-1 well-log suite, comprising of the caliper, gamma-ray, neutron, and density logs and the Galula-1 well-log suite comprising of gamma-ray, spontaneous potential, resistivity, and sonic logs. Based on the petrophysical analysis, five sand zones were delineated in each well: (A-E) in the Galula-1 well and (1-5) in the Ivuna-1 well. According to this study, the RSG in both the Galula-1 and Ivuna-1 wells is dominated by clastic facies with interbedded thin shale and was most likely deposited in fluvial and fluvio-lacustrine environments. The delineated sand zones in Galula-1 well have shale volumes ranging from 28.8% to 36.1%, high effective porosities ranging from 30.1% to 32.6%, high permeabilities ranging from 88.45 mD to 121.39 mD, 100% water saturation, and no hydrocarbons. The five delineated reservoirs in Galula-1 well have high effective porosities ranging from 25.8% to 28.8%, high permeabilities ranging between 45.92 mD and 71.91 mD, and are 100% water saturated but lack hydrocarbons. As a result, the RSG of the Galula-1 well was assessed to have good petrophysical properties and is a potential hydrocarbon reservoir given the presence of hydrocarbons. By contrast, the delineated sand zones in Ivuna-1 well have shale volumes ranging from 26.4% to 35.6%, very low effective porosities ranging from 0.011% to 0.038%, and poor permeabilities ranging from 0.007 to 0.117 mD. Further, the two delineated reservoirs in Ivuna-1 well are thin and have very low effective porosities ranging between 0.112% and 0.106% and poor permeabilities ranging between 1.33 mD and 1.64 mD. Consequently, the RSG of the Ivuna-1 well was evaluated as having poor petrophysical properties and is not a suitable hydrocarbon reservoir. This study also revealed that the porosity and permeability of the RSG declines greatly from the Galula-1 well to the Ivuna-1 well. Nevertheless, more research is recommended to validate this revelation. This study further, recommends more research into the porosity and permeability of the RSG through petrography and core analysis. The findings of this study will contribute to academic, geologic, geophysical, and hydrocarbon research of the RSG and Rukwa Basin at large.