Integrated Petrophysical Evaluation and Reservoir Characterization of the Zarama Field, Offshore Niger Delta Using Multi-Well Geophysical Log Analysis

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.