Advanced Seismic Data Interpretation for Carbonate Targets Based on Optimised Processing Techniques.

Abstract

The Shuaiba Fm. represents one of the most prolific hydrocarbon reservoirs in Abu Dhabi. The remaining potential is supposed to be related to subtle structural and stratigraphic traps. New developments in exploration geophysics like prestack depth migration integrating processing and interpretation form a powerful tool for improved development of existing oil fields and for identification of new oil fields.

In general the processing comprises three phases (depending on the local validity/violation of the zero-offset (zo)-condition, i. e. to which extent does the DMO-stack represent a zo - volume):

Phase A: Standard processing sequence up to final DMO stack and migration including calibration using elastic instead of plane-wave synthetic seismogram. The interpretation team generates a first macro model of the velocity field.

Phase B: Poststack depth-domain

The velocity field is checked and updated using the wavefront method. The new macro model forms the basis for poststack depth migration, which is reinterpreted by the interpretation team in order to confirm / update the reflector geometry and to generate the final macro model required for

– Phase C: Prestack depth-domain.

The prestack depth migration is subject to final interpretation and - due to the irregular surface of the Shuaiba Fm. - should form the basis for AVO. Further steps are L-l- deconvolution followed by Born inversion, which is essential for generation of a high resolution lithological model.

The procedure is presented using a 2D seismic line, which was subject to a detailed interpretation (seismic sequence and facies analysis) of the Shuaiba Fm. The final result is a detailed lithological model which is verified by applying elastic forward modeling ("verification loop's"). The results are to be used as input in reservoir modeling and geostatistical evaluations in order to take into account reservoir heterogeneities being important for prospect evaluation.

Introduction

Geology and Stratigraphy of the Shuaiba Fm in Abu Dhabi. The shallow water carbonates of the Lower Cretaceous Shuaiba Fm (Upper Thamama Group, Aptian) was deposited on a vast shelf covering the eastern Arabian Peninsula. The formation of intrashelf basins resulted in the establishment of facies belts i. e.

  • shallow water shelf carbonates

  • a buildup prone belt rimming the intrashelf basin centered in Abu Dhabi and

  • basinal deposits in the intrashelf basin areas.

The shelf margin buildups - mainly rudist buildups - of the belt rimming the intrashelf basin today form the most prominent hydrocarbon reservoirs (Frost et. al., 1983). The shallow water shelf carbonates however may represent a potential reservoir due to increased porosity resulting from subarea exposure and weathering by meteoric waters during the Bab relative sealevel lowstand.

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