IMPACT OF 3D SEISMIC VELOCITES ON DEPTH CONVERSION AND RESERVOIR VOLUMETRICS IN “AKOS FIELD”, ONSHORE NIGER DELTA

EARTHSCIENCES

The study investigated 3D seismic velocities as playing a vital role in accurate depth conversion and volumetrics using the “Akos field” as a case study to be revisited for previously bypassed information as well as enhanced information on estimation of target depth and volumetrics. The data set available for this research included well and Log data for the fourteen wells within the field which aided in enhanced understanding of the lithostratigraphic and petrophysical properties of the field. The logs were generated using various equations suitable for reservoir sands of the eastern Niger Delta. Data set also included Checkshot data, seismic and stacking velocities for seismic analysis and creation of models. The methodology of the study covered Data gathering, quality control, correlation, delineation of lithofacies, depostional environment and relevant petrophysical property acquisition, seismic analysis, seismic to well ties, time depth relationship, creation of velocity model and analysis. Part of the interpretation from some of the data has revealed deltaic shoreface deposits comprising channels, tidal channels and barrier bar sheet sands found within a paralic sequence. The field also generally followed the more typical (Niger Delta) case of natural pressure support from radial to semi radial aquifers in all but a few numerous stacked reservoirs. Reservoir performance was generally by water drive. The petrophysical properties revealed a porosity that ranged from 20% to 30%. Correlation of the wells revealed a lot of structural complexities within the field because of differences between depth and field prognosis. The presence of a sidetrack was noted at well 12 being situated close to a fault with considerable sealing properties. The field is an elongated eastwest rending footwall closures developed against a boundary fault and consists of 3 major accumulations. Main oil accumulations lie between 6500ft subsea and 11500ft subsea at the central part of the field. Various velocity models were applied to depth conversion and volumetrics and the most suitable with respect to volumetric output, closeness to zero offset, “fit to well” and formation dependence was identified. This study may prove to be useful in the creation of a reference material for marginal field operators and operator of fields that are being revisited.

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