Petrophysical analysis of the red sandstone group of The Rukwa Graben, Southwestern Tanzania
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Date
2021
Authors
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Journal ISSN
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Publisher
The University of Dodma
Abstract
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.
Description
Dissertation (Msc Petroleum Geosciences)
Keywords
Sand, Petrophysical properties, Sandstone, Petrography, Reservoir zones, Red Sandstone Group, RSG
Citation
Ojok, T. (2021). Petrophysical analysis of the red sandstone group of The Rukwa Graben, Southwestern Tanzania (Master's Dissertation). The University of Dodoma, Dodoma.