The development strategy for a green reservoir with a huge gas resource needs to be evaluated based primarily on the presence or otherwise of a possible economic oil column below this gas cap, as well as on other pertinent reservoir property distributions. The evaluation process requires the integration of all available and credible geoscience and engineering information to help justify and support the correct assessment of key elements and options in the development strategy. The only well that penetrated this structure encountered a "gas-down-to" (GDT) within the upper reservoir interval. The objective is to assess the possibility of the existence of an oil rim below the GDT and to estimate the depth of a possible GOC and the associated degree of confidence. This assessment needs to be done to support a robust hydrocarbon development strategy and to secure approvals from regulatory authorities. This paper details the use of 3D seismic attribute analysis and forward seismic modelling combined with static reservoir modelling and scenario management to delineate the fluid contacts and to constrain the inherent uncertainties. The direct hydrocarbon indicator (DHI) observed on the 3D seismic data across the field exhibits an excellent structural fit and yielded a robust fluid contact definition. The use of quantitative seismic amplitude analysis as well as scenario synthetic matches with real seismic data was invaluable in guiding the selection of a feasible development option and securing the necessary approvals.
Following the present global economic crises and the huge impact on energy prices, the industry is taking a pretty hard look at its development portfolio and is frantically searching for new and cheaper processes and workflows to help reduce costs, minimize risks and maintain a reasonable bottomline. Within the past few years quantitative seismic reservoir analysis has grown in popularity following a catalogue of successful results worldwide. With the robust tools and smart workflows at our disposal today, quantitative reservoir characterisation methods now represent a relatively cheap, fast and affordable technique for identifying and delineating hydrocarbon reservoirs in both carbonate and clastic regimes.We have implemented a rigorous simultaneous inversion workflow to analyse pre-stack seismic amplitude data and well logs from shallow offshore Niger Delta basin. Two partial angle stacks were simultaneously inverted to generate a 3D distribution of P-impedance, S-impedance, and density over the ROK reservoir interval. The pre-stack seismic inversion results and the modulus attributes derived from the main inversion products provided quantitative information about the geometry as well as the spatial distribution of highly-viable hydrocarbon bearing rocks across the field. The Monte Carlo and Bayesian analysis yielded predictions consistent with the results of the quantitative measurements.
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