High Resolution Sequence Stratigraphy Correlation and Sedimentary Model of Braided Rivers: A Case on Paleogene Palogue Oilfield, South Sudan

摘要

Complicated fluvial sands correlation and braided river models are still challenges for heterogeneous anisotropic reservoir evaluation for petroleum development in oilfields. Based on high-resolution sequence stratigraphy and sedimentology, core observation, and the analysis of logging and seismic data, high-resolution sequence stratigraphy framework of Paleogene Yabus formation of Palogue Oilfield, South Sudan is established, and sedimentary characteristics of braided rivers are analyzed, (1) In braided river deposits, channel bars are usually pro-gradating seawards and going thicker upwards. And braided channels are retro-gradating landwards and going thinner upwards. Both of them can be subdivided into channel (bar) trunks and channels (bar) flanks, showing vertical stacking and lateral migration; (3) As the A/S (Accommodation space/sediments supply) increasing upwards, braided river sands are shifting frequently as a reciprocating migration in Yabus V/VI, and they are more stable as the A/S decreasing upwards as a vertical aggradation in Yabus VII/VIII; (4) With 77 wells sedimentary microfacies identification, sand thickness and sand/bed ratio distribution, sedimentary facies distribution of all members and zones are analyzed. According to the A/S change, three braided river models are concluded, including isolated channel type (high A/S period), crossed channels type (medium A/S period), and superposed channels type (low A/S period).