preprint · Preprints.org
A multi-well petrophysical evaluation of the offshore Zarama field in the Niger Delta basin assessed reservoir quality, heterogeneity, and producibility within the Agbada Formation using wireline logs from five wells. The reservoirs exhibit good to excellent porosity between 20 and 32 percent, declining with depth due to compaction, while permeability ranges widely from 7 to 781 millidarcies, driven primarily by shale content. Reservoir units span from 6-metre beds to thick intervals exceeding 700 metres, with lateral continuity observed across several massive sands containing high hydrocarbon pore volumes. Integrated log analysis identified fluid interfaces and estimated recoverable reserves of approximately 2.85 million barrels of oil equivalent and 5.85 billion cubic feet of gas. Overall, the field is predominantly gas-bearing with minor oil and condensate accumulations, forming a complex, heterogeneous multi-reservoir system that requires integrated multi-well analysis for effective development planning.
Understanding the distribution of hydrocarbons in complex offshore deltaic environments is essential for effective energy resource assessment. By combining multiple geophysical logs, this evaluation establishes reliable estimates of gas and oil reserves in the Niger Delta. These findings provide clarity on subsurface fluid interfaces and rock quality, helping operators reduce exploration uncertainties and design more effective reservoir development strategies in geologically challenging offshore settings.
The work provides petrophysical parameters and reserve estimates that upstream energy companies can use to guide field development planning and well placement in the offshore Niger Delta. Because the findings are based on applied multi-well log evaluations, they offer direct operational insights for field characterisation, though actual commercialisation remains subject to subsequent drilling, field testing, and production engineering.
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In this paper, a multilateral petrophysical analysis of the Zarama field is undertaken, based on a complete set of well-wireline logs, the gamma ray, resistivity, density, and neutron logs of five wells (Wells 1-5). Emphasis is placed on important reservoir parameters, including porosity, permeability, shale volume, and fluid saturations as an effort to determine the quality of the reservoir, its heterogeneity, and producibility in the case of Agbada Formation in the Niger Delta basin. The results indicate that the reservoirs are of good and excellent porosity, with 20 to 32 percent of the reservoirs, which tends to decrease with depth due to the compaction occurrences that are dominant in offshore settings. Yet, the variation in permeability is high (7 to 781 mD), although it is more dependent on shale content (Vsh) rather than porosity as a single factor. Thicknesses of the reservoirs range between thin beds (approximately 6 m) and thick units more than 700 m, with lateral continuity being observed alongside some of the more numerous massive sands (e.g., S1, S3, S14, S16) with high hydrocarbon pore volumes and good production prospects. Interpretation of interfaces between hydrocarbon fluids, i.e., gas-water, gas-oil, and oil-water, between layers was done by integrated log analysis even in the absence of data and density log anomalies due to the presence of gas. The estimated reserves show recoverable volumes of around 2.85 million barrels of oil equivalent and 5.85 billion cubic feet of gas, which speaks to the field’s promising yield. The study highlights the fact that the gas reservoirs are dominant, with small accumulations of oil and condensate. The field is mainly gas bearing with inners of oil /condensate, as shown by the log response and neutron-density crossovers. Petrophysical ties between wells have highlighted a multi-reservoir system that is heterogeneous, but without well-defined stratigraphic trappings, and requires a multi-well exploration using integrated interpretation to allow proper characterization and reservoir development planning. The present work highlights the relevance of integrated log interpretation to address shortcomings of datasets in isolation and offers revised petrophysical parameters at a high level of confidence, as well as estimating appreciable recoverable reserves. The Zarama field shows complexities of lithological and fluid variations in the gas-dominated deltaic environment in which it is a potential offshore hydrocarbon province.
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DOI: 10.20944/preprints202509.0568.v1
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