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- ItemA review on the provenance of the Voltaian Basin, Ghana: Implications for hydrocarbon prospectivity(Scientific African, 2022) Zobah, Theresa Ngmenmaaloo; Adenutsi, Casper Daniel; Amedjoea, Godfrey Chiri; Wilsona, Matthew Coffie; Boateng, Cyril D.; Quaye, Jonathan Atuquaye; Erzuah, Samuel; Wang, Lian; Zhao, Guoxiang; Karimaie, Hassan; Danuor, Sylvester Kojo; 0000-0002-1721-4158The Voltaian Basin of Ghana has taken significance as a potential oil and gas basin. Since Ghana became a petroleum-producing country, every attempt is being made to understand the sedimentary basins within the country’s territorial boundaries, particularly, the Voltaian Basin. This review paper investigates studies on the Voltaian Basin drawing on a comprehensive literature review based on database searches from Scopus, Web of Science, and Science Direct, among others. Several branches of geology such as mineralogy, geochemistry, igneous and metamorphic petrology, geochronology, and sedimentary geology among others were integrated to reconstruct the source of the Voltaian Basin sedimentary rocks. Application of compositional analyses to determine provenance using petrographic, mineralogical, and geochemical techniques are also discussed. Results based on articles retrieved from the comprehensive literature review summarize the findings on provenance studies; stating the sediment source and history of the rock types in the Voltaian Basin to be most likely from the Pan-African orogenic rocks having a felsic source with some inputs from metasedimentary source rocks. Findings from provenance studies further point to the depositional environment being of shallow marine source and having a fluvial to deltaic environmental features, suggesting that the depositional environment is suitable for hydrocarbon source rocks as well as reservoir rocks formation. With regards to petroleum exploration, a lot of research work needs to be done to identify the type of sedimentary organic matter present in the shales and the limestones of the Voltaian Basin. Furthermore, the rock properties that define petroleum reservoirs such as porosity, permeability, pore type, and rock compressibility as well as electrical properties of some important sandstones need to be thoroughly investigated.
- ItemAn integrated fracture parameter prediction and characterization method in deeply-buried carbonate reservoirs based on deep neural network(Journal of Petroleum Science and Engineering, 2022) Yasin, Qamar; Ding, Yan; Baklouti, Syrine; Boateng, Cyril D.; Du, Qizhen; Golsanami, Naser; 0000-0002-1721-4158However, fracture prediction in deeply buried carbonate reservoirs has always been challenging. Fracture prediction in the deep-buried carbonate structure of North China is problematic because of multiphase tectonic movements, variable sediment lithology, and complex diagenesis. Because of deep burial depth and complex heterogeneity, the resolution of seismic reflection data beneath the buried-structure is poor, making it challenging to identify the fault reflection characteristics. This paper proposes a novel idea to identify natural fractures in carbonate reservoirs using conventional logs with seismic reflection data. The proposed model can also predict the fracture aperture and fracture density, a distinctive feature. Another novel hybrid model based on deep-learning neural network (DNN) and cluster analysis is proposed to predict further the spatial variations of lithology, porosity, and fracture parameters from seismic inversion. The proposed models provide valuable insights that help determine fracture parameters in the Paleozoic strata and associated reservoirs through quantitative analysis using petrophysics, rock physics, seismic inversion, and seismic attributes. The overlapping of seismic interpreted fault networks and spatial variations of the inverted fracture parameters indicate a high correlation of fracture development zones. The methodology proposed in this study presents a valuable template valid for the characterization of fractured reservoirs in deeply-buried carbonate reservoirs throughout the world.
- ItemBiogenically modified reservoir rock quality: A case from the lowermost member Paleocene Funing Formation, Gaoyou Depression, Subei Basin, China(Journal of Petroleum Science and Engineering, 2022) Quaye, Jonathan Atuquaye; Jiang, Zaixing; Liu, Chao; Adenutsi, Casper Daniel; Boateng, Cyril D.; 0000-0002-1721-4158Bioturbation can influence reservoir quality and is consequential to the producibility of a reservoir. The study of samples from the lowermost member of the Paleocene Funing Formation (E1f1), Gaoyou Depression, Subei Basin, shows how bioturbation affects reservoir quality. Techniques used to study the samples include petrography, pressure decay porosimetry, pulse decay permeametry, Field Emission Scanning Electron Microscopy, and Energy Dispersive X-ray Spectroscopy. Sample A is intensely burrowed by Taenidium, Scoyenia, Skolithos, Palaeophycus, and other trace fossils. Increased isotropy in sample A contributes to cleaner well-sorted burrows, relative to its surrounding matrix, and 67.18% augmented burrow porosity. Taenidium and Palaeophycus in sample B indicate 20.23% improved burrows porosity. Plant debris and/or root traces in sample C have a 3.68% reduction in porosity. In samples A and B, the arithmetic mean of permeability describes all horizontal fluid flows within burrows. In sample C, the geometric mean of permeability describes the fluid flow in all directions. Porosity is ≤ 11.2%, permeability ≤1 md in samples, and sample C log-derived porosity ≤0.33%. This study demonstrates that bioturbation together with depositional factors (sorting, grain size distribution, and mud matrix/burrow content) and diagenetic modifications (albitization, compaction, dissolution, kaolinization, and precipitation) control the quality of the high to intensely bioturbated (Bioturbation Index 4 to 5; 61–99 vol %) sandstone and siltstone reservoir facies of the E1f1.
- ItemCharacterization of complex fuvio–deltaic deposits in Northeast China using multi‑modal machine learning fusion(Scientific Reports, 2020) Boateng, Cyril D.; Fu, Li‑Yun; Danuor, Sylvester K.; 0000-0002-1721-4158Due to the lack of petroleum resources, stratigraphic reservoirs have become an important source of future discoveries. We describe a methodology for predicting reservoir sands from complex reservoir seismic data. Data analysis involves a bio-integrated framework called multi-modal machine learning fusion (MMMLF) based on neural networks. First, acoustic-related seismic attributes from post stack seismic data were used to characterize the reservoirs. They enhanced the understanding of the structure and spatial distribution of petrophysical properties of lithostratigraphic reservoirs. The attributes were then classifed as varied modal inputs into a central fusion engine for prediction. We applied the method to a dataset from Northeast China. Using seismic attributes and rock physics relationships as input data, MMMLF was performed to predict the spatial distribution of lithology in the Upper Guantao substrata. Despite the large scattering in the acoustic-related data properties, the proposed MMMLF methodology predicted the distribution of lithological properties through the gamma ray logs. Moreover, complex stratigraphic traps such as braided fuvial sandstones in the fuvio–deltaic deposits were delineated. These fndings can have signifcant implications for future exploration and production in Northeast China and similar petroleum provinces around the world.
- ItemEvaluation of porosity and permeability of sandstones within the Oti Group of the Volta Basin using petrophysical and petrographic techniques(Journal of the Ghana Institution of Engineering, 2023) Zobah, Theresa N.; Adenutsi, Casper D.; Amedjoe, Godfred C.; Wilson, Matthew C; Mensah, Emmanuel; Boateng, Cyril D.; Sarpong, Kwame K.; Opuni, Lydia N. O.; Danuor, Sylvester K.; Karimaie, Hassan; 0000-0002-1721-4158This study investigates the reservoir quality of sandstones in the Oti Group of the Volta Basin of Ghana. Geological field mapping, petrographic, petrophysical, mineralogical, and geochemical techniques are used to investigate the reservoir parameters of the sandstones by evaluating the fluid holding and transmission capabilities of the rocks. Results from the comprehensive study identified two sandstone formations of interest; viz. the Bimbila Sandstone and Yabraso Sandstone. Both sandstones were found to be quartz sandstones (sub-arkose and quartz arenites). The Bimbila Sandstones proved to have better porosity and permeability as compared to the Yabraso Sandstones. The Yabraso Sandstone showed porosity between 7-22 % with an average porosity of 13 % (helium gas) and permeability of 63.41 mD, which may be linked to intense cementation and intermediate compaction as well as grain size, shape and arrangement. The Bimbila Sandstones showed better porosity and permeability with a porosity range of 6-24 %, an average porosity of 14 % (helium gas) and 131.80 mD permeability. This is seen to be due to lower compaction supported by framework-stable quartz resulting in a well-connected pore system with high permeability. Further mineralogical data show that the clay minerals present are in minor concentrations. Also, the position of the Yabraso and Bimbila Sandstones in the project area as plotted on the geological map show that there is a close proximity relationship between these sandstones and the limestones; hence forming a conducive system such that if hydrocarbons are produced by the possible source rocks (limestones), they can be housed by the sandstones.
- ItemEvaluation of shale gas reservoirs in complex structural enclosures: A case study from Patala Formation in the Kohat-Potwar Plateau, Pakistan(Journal of Petroleum Science and Engineering, 2021) Yasin, Qamar; Baklouti, Syrine; Khalid, Perveiz; Ali, Syed Haroon; Boateng, Cyril D.; Du, Qizhen; 0000-0002-1721-4158Breakthroughs in shale gas exploration and production technology in China point to a possible solution to Pakistan’s current energy crises. In this study, we evaluate the shale gas prospects in the Kohat-Potwar Plateau of Pakistan by establishing an integrated approach involving the analysis of fundamental elastic and petrophysical properties, Rock-Eval pyrolysis, and the sealing mechanism of shale. Detailed geochemical and petrophysical evaluation of the Patala Formation in the Kohat-Potwar Plateau indicates the good potential for shale gas with the following characteristics similar to the Longmaxi shale of Sichuan Basin China, i.e., (i) complex structural types sandwiched by tight limestone strata with low porosity (less than 3%), ultra-low permeability, high density, and large thickness which provides strong sealing capacity for gas preservation and enrichment; (ii) multiphase tectonic evolution of Patala Formation allowed various slippage processes to develop fractures and enhance the porosity and permeability; (iii) high organic matter content and thermal maturation stage (TOC >2%, 416–445 ◦C); (iv) high brittle minerals content (e.g., calcite and dolomite > 40%); and (v) large formation thickness (>30 m) at shallow burial depth < 2500 m. This study emphasizes the critical role of the sealing mechanism in shale gas reservoirs. Furthermore, the results suggest that the evaluation and development of shale gas potential using petrophysical and geochemical analysis may be inadequate. Further scrutiny of the roof and floor of reservoirs’ efficient sealing capacities is essential to understand the extent of shale gas preservation and enrichment. The study results provide valuable insights for identifying the sweet spots and preservation condition of shale gas in the Kohat-Potwar Plateau of Pakistan.
- ItemInvestigation of Groundwater In-rush Zone using Petrophysical Logs and Short-offset Transient Electromagnetic (SOTEM) Data(Journal of Environmental and Engineering Geophysics, 2020-09) Khan, Muhammad Younis Khan; Xue, Guo-Qiang; Chen, Wei-Ying; Boateng, Cyril D.; 0009-0007-4072-0968; 0000-0002-1721-4158The water burst from the Ordovician limestone underlain by the Permo-Carboniferous coal seams have potential to trigger coalmine hazards in Northern China. Therefore, it is crucial to identify and accurately map the water enrichment zones and delineate coal seams using an integrated approach based on surface TEM and subsurface wireline log information to avoid water-inrush hazard and ensure safe production of coal. We inverted surface based TEM data using 1-D Occam inversion to identify the conductive anomaly and then further quantified the zone of interest by gamma and resistivity logs. 1-D Occam inversion results show conductive zone around 370 m while higher resistivity and lower gamma ray log signatures were observed against coal seams. Groundwater inrush zone falls within the mid-range gamma ray and resistivity interval as shown on the petrophysical logs. The distinct log signatures (low gamma-ray and high resistivity values) clearly indicated coal seams at depth of 410 and 470 m and subsequently the log trends were used to distinguish between coal units and more permeable sands. The magnitude and the variability of these parameters in the borehole are attributed to the subsurface stratigraphic heterogeneity. They can be key clues for interpretation of depositional facies of coal-bearing sequence and may also be used as a constraint in characterization of groundwater enrichment zone.
- ItemRock type prediction and 3D modeling of clastic paleokarst fillings in deeply-buried carbonates using the Democratic Neural Networks Association technique(Marine and Petroleum Geology, 2021) M'endez, Jos´e N.; Jin, Qiang; Zhang, Xudong; Gonz'alez, Maria; Kashif, Muhammad; Boateng, Cyril D.; Zambrano, Miller; 0000-0002-1721-4158This study outlines a probabilistic model based on artificial neural networks applied to the deeply-buried karsted carbonates of the Ordovician Yingshan Formation, which represent significant oil reservoirs in western China. The complexity of both rock type prediction and 3D facies modeling of paleokarst fillings, which are hosted within the cavities, drives the need to apply innovative techniques for identifying new oil plays. Due to the high heterogeneity of clastic fillings and patchy continuity of the karst patterns, physical evaluation of these reservoirs is extremely complex. We propose the Democratic Neural Networks Association (DNNA) as the probabilistic technique to solve these challenges. This technique simultaneously runs several artificial neural networks in parallel and combines seismic data and well logs. The resulting probable facies volume is expected to provide an appropriate distribution and delineation of clastic fillings (i.e., conglomerates, fine-grained sandstones, silt stones, mudstone, dolomite fragments, and sparry calcarenite) and unfilled or empty spaces. This calculated volume is then used as a reliable input data to condition trend analysis on a very fine geological grid, in order to model the complex patterns in question. The static model obtained shows that, the probabilistic distribution of each filling has the same orientation as karst system. Likewise, spatial dimensions similar to the proposed analogue model of these patterns (vertical and horizontal scales) are delineated. Finally, we validated prediction results by comparing them with the interpreted karst facies of a well not initially considered in the 3D model. The results indicating that the DNNA technique proves to be a useful innovative tool for generating realistic de pictions of fillings deposited within deeply-buried paleokarst.
- ItemStudy on brittleness templates for shale gas reservoirs-A case study of Longmaxi shale in Sichuan Basin, southern China(Petroleum Science, 2021) Yasin, Qamar; Sohail, Ghulum Mohyuddin; Liu, Ke-Yu; Du, Qi-Zhen; Boateng, Cyril D.; 0000-0002-1721-4158Differentiating brittle zones from ductile zones in low permeability shale formations is imperative for efficient hydraulic fracturing stimulation. The brittleness index (BI) is used to describe the rock resistance to hydraulic fracture initiation and propagation and measures the ease at which complex fracture net works can be created. In this study, we constructed brittleness templates through the correlation of fundamental rock properties and geomechanical characterization. We then employed the templates to distinguish the brittle, ductile, and brittle-ductile transition zones in the Longmaxi shale gas reservoir, Sichuan Basin of southern China. The approach works in two steps. First, we suggest a new expression for the mineralogical BI by their respective weights based on the analysis of correlation coefficients between mechanical testing and XRD results. Second, we correlate TOC, porosity, pore fluid, natural fractures, and improved BI model with multiple elastic properties to define the brittle, ductile, and transitional zones in the Longmaxi shale gas reservoir of China. Compared with the traditional mineralogy-based BI definition, the improved BI model differentiates the brittle and ductile zones and provides a better sense of the most suitable fracturing regions. Our results show that the brittleness templates, which combine fundamental rock properties, improved BI model, and geomechanical characterization led to identifying favorable zones for hydraulic fracturing and enhanced shale characterization. The proposed brittleness templates’ effectiveness was verified using data from horizontal wells, offset wells, shale gas wells from different origins, laboratory core testing, and seismic inversion of BI across the studied wells.
- ItemUnderrepresentation of Local Researchers in Geophysical Studies at the Bosumtwi Impact Crater: Insights from A Systematic Review(Scientific African, 2023) Boateng, Cyril D.; Akrugu, Christopher A.; Wemegah, David D.; Danuor, Sylvester K.; 0000-0002-1721-4158Impact cratering is an important aspect of planetary evolution. Geophysics plays a complementary role in identifying impact craters on Earth given the non-unique geological characteristics associated with such craters. The Bosumtwi impact crater in Ghana represents one of the world’s most well-preserved and young mid-sized impact craters, and this study aims to evaluate the current state of geophysical research conducted in this area. The Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) technique was employed for data collection and analysis, which involved identifying and screening relevant sources of data. Results indicated that the maximum number of publications (14) on the Bosumtwi impact crater was recorded in 2007, with 15% of these articles being affiliated with Ghanaian institutions. Furthermore, only two articles reported funding from Ghana. The major geophysical methods applied in studies of the Bosumtwi impact crater include various techniques that have confirmed the presence of shock metamorphosed rocks. Although geophysical methods cannot provide unambiguous evidence for an impact origin of the Bosumtwi crater, they did provide additional constraints in estab lishing its impact origin. This study highlights the lack of local financial support for research in Ghana and African countries in general, with the underrepresentation of Ghanaian geophysical researchers being a concerning outcome. The absence of hazard studies such as the creation of unstable cliffs and the long-term effects of the meteorite impact on inhabitants of the Bosumtwi impact crater is particularly significant. Further research is necessary to fully understand the implications of this underrepresentation. Moreover, this study highlights the importance of research at the Bosumtwi impact crater for achieving the UN Sustainable Development Goals.