Reservoir Characterization and the Quantitative Assessment of Hydrocarbon-Bearing Reservoir Sands in the Otodi Field, Niger Delta

Abstract

An integrated petrophysical and seismic reservoir characterization study was carried out in the Otodi Field, eastern Niger Delta, Nigeria, to evaluate reservoir quality and estimate hydrocarbon reserves. The study utilized a post-stack, time-migrated 3-D seismic volume (234 km²) together with wireline log suites, checkshot, and deviation data from four wells (KC1–KC4). Usable open-hole log suites (gamma ray, resistivity, density, sonic, neutron and caliper) were available for wells KC1–KC3, while KC4 was limited to checkshot data and was used only to support the regional time–depth framework. Petrophysical parameters such as shale volume, porosity, water saturation, hydrocarbon saturation, and permeability were computed in Petrel™ using standard empirical relationships (Schlumberger, 1974; Asquith & Krygowski, 2004; Hartman & Beaumont, 1999). Three hydrocarbon-bearing reservoir sands (I, II and III) were delineated. Porosity ranges from 19% to 28% (good to very good) and permeability from 60 mD to 477 mD (fair to very good), with hydrocarbon saturation ranging from 77% to 96%. Reservoirs I and III exhibit markedly better porosity and permeability character than reservoir II. Volumetric modelling yielded Stock Tank Oil Initially in Place (STOIIP) of 6,090 (×10³ bbl), 4,381 (×10³ bbl) and 5,658 (×10³ bbl) for reservoirs I, II and III. On this basis, reservoir I is the prospective hydrocarbon target in the field, followed by reservoir III, with reservoir II ranked as the least prospective of the three sands. Structurally, the field is dominated by a rollover-anticline trap style associated with NE–SW-trending listric growth faults, consistent with the regional structural style of the Niger Delta.