Enhancing the Interpretation of Rift Structures in Sudan Using AVO Analysis and Seismic Inversion

Uncertainty in structural complexities and rock heterogeneities is a major challenge that controls oil exploration and drilling operations in the rift basins of Sudan. Wide ranges of depositional environments developed within these reservoirs: e.g., fluvial, shallow and deep lacustrine, fluvio-deltaic systems. Multi-phase rift development from rift initiation to late post-rift introduced good oil traps and very heterogeneous reservoir rocks situations.

Advances in seismic inversion techniques and AVO analysis maximize the probabilities of valid interpretation and lithology delineation in such rift structures thereby reducing the associated uncertainty limit. Accuracy of interpretation depends on the quality of seismic data. Therefore, there is an urgent need to introduce innovative techniques in seismic processing to improve seismic resolution prior to any inversion work.

This paper explains an-integrated workflow using seismic inversion applied for detailed interpretation and advanced reservoir characterization applications in these rift basins. This workflow involves three phases: starting with detailed sedimentological analysis; next AVO seismic inversion; finally cross validation and uncertainty analysis.
The seismic data conditioning and inversion workflow implementation comprises three main steps: beginning with data conditioning (seismic and logs), wavelet estimation, and relative acoustic impedance inversion (RAI).The conditioned seismic and RAI volumes are used to improve the interpretation of horizons and build a low-frequency model (LFM). The final step of the workflow is to perform absolute acoustic impedance inversion (AAI), porosity transformation, and depth conversion.
Using rock physics analysis for well logs, the acoustic impedance and porosity relationship at the reservoir intervals is cross-correlated and established. This relationship is used to transform high-resolution acoustic impedance inversion to porosity and, subsequently to identify facies and lithological variations. The results of this study show that seismic resolution and interpretation can be improved using AVO seismic inversion.