High Resolution Sequence Stratigraphy Correlation and Sedimentary Model of Braided Rivers: A Case on the Yabus Formation in Pal Block of Palogue Oilfield, South Sudan 3/7 Area

Abstract

Abstract: Complicated fluvial sands correlation and braided river models are still challenges for heterogeneous anisotropic reservoir evaluation in the world. Based on high resolution sequence stratigraphy and sedimentology, with the analysis of cores, logging and seismic data, high resolution sequence stratigraphy framework of Paleogene Yabus formation in the Pal block of Palogue Oilfield, South Sudan 3/7 Area is established, and sedimentary characteristics of braided rivers are analyzed, (1) two kinds of sedimentary subfacies and five kinds of microfacies of braided river deposits are identified, including channel subfacies (i.e., braided channel, channel bar, channel suspension) and inter-channel subfacies (i.e., overbank, flooding plain fine deposits); (2) In the major braided river sands, channel bars are usually prograding seawards, and go thicker upwards. Braided channels are retrograding landward, and go thinner upwards. Both of them can be subdivided into channel (bar) trunks and channels (bar) flanks, and sands are overlaid vertically and reciprocated laterally; (3) Braided river sands correlation indicates that sands continuity is good along with the source supply direction (SSD), and is relatively bad vertical to the SSD. As the A/S (Accommodation to source supply ratio) is 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 is 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 every member and zone are analyzed. According to the A/S change, three types of braided river models are concluded, including isolated channel type (in high A/S period), crossed channel type (in medium A/S period), and superposed channel type (in low A/S period). Key words: HRSS, braided river, depositional law, sedimentary model, South Sudan

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015