Journal de géologie et géophysique
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Integrated 3-D Reservoir Evaluation and Sequence/Seismic Stratigraphic Interpretation of “Topa’’ and “Obi” Fields, Niger Delta, South-South, Nigeria

Hilal Al -Zeidi , Hamdan Ali, Obichukwu Paul Tochukwu, Njoku Ikechukwu, Onyekuru Samuel, Selemo Alexander, Nwigbo Ukamaka, OsungWilson, Osahon Usen

The inter-fingering and complexity of the subsurface seismic-reflection configurations, motives and patterns in the ‘obi’ and “topa” fields, niger delta have no doubt indicated high possibilities of bypassed petroleum reserves within the fields. Integrated workflow is utilized in this research and aimed at unravelling the potentials as well as predicting the hydrocarbon availabilities in most of the bypassed reservoirs within “topa” and “obi” fields. The data used include: 3d seismic data; well data, and biostratigraphic data. This data set were applied in the study for reservoirs delineations and identifications encompassing structural fault interpretations, depth structural maps, direct hydrocarbon indicators, petrophysical evaluations, 3d reservoir modeling and seismic stratigraphic analysis. Also, amplitude extraction such as semblance volume, enhanced structural smoothing as well as root means square (rms) attributes were generated. The semblance volumes were used to ascertain both lateral and vertical extent of the structural geometries while the enhanced structural smoothing were used to accurately interpret the faults, the rms amplitude was used to interpret the seismic reflectivities such as the bright spots and the flat spots were there no direct hydrocarbon indicators. Also, petrophysicalevaluations were carried out and the results indicated good effective porosities in all the studied reservoirs with an average of 35% within net-to gross sand reservoirs of at least 75% average. The determined acoustic impedance log was spasmodically skewed with chronostratigraphic packages within genetic units. Results show that “obi” field has a more complex structure when compared to “topa” field. Seismic stratigraphy of “topa” field revealed a sub-parallel to slightly divergent reflection configuration indicating a possible increase in sediment deposition by virtue of the accommodation space created by earlier subsidence or faults. Topa field is mostly stratigraphically dependent with slide structural impacts. Two bright spots were observed in “obi” field suggesting the presence of hydrocarbon as well as having good lateral extensions with faults forming closures. However, “obi” and “topa” fields vary both stratigraphically and structurally as revealed with the aid of seismic attributes. A demonstration of typical accumulation of oil in one of the studied field is shown using obi c_6000 reservoir and this indicates 691 ft of oil column height, hydrodynamic oil drive of 85 ft water within a 776 ft vertical relief of the reservoir. However, these vary from one reservoir to another.