Sedimentary Characteristics and Reservoir Model of Distant Braided Delta Deposits: A Case on Upper Cretaceous Yogou Formation of Termit Basin, Niger

Abstract

Finding good reservoirs in thin sand and thick shale layers is still a challenge for hydrocarbon exploration. Based on the high-resolution sequence stratigraphy theory and the establishment of high-resolution sequence stratigraphy framework with seismic-well tie, the dynamic deposition process of braided delta sands on late Cretaceous Yogou formation has been analyzed on 62 wells, 2D seismic data of 13026 km and 3D seismic data of 11607 km2 in passive rifting Termit basin with multi-stages depressions and reversals. (1) Six kinds of sedimentary microfacies and three major reservoir sands with multi-stages vertical stacking and lateral migration are in late Cretaceous Yogou formation; (2) Based on accommodation space/Sediments supply change and depositional progress, sedimentary facies distribution evolution has been done according to sedimentary micro-facies statistics and narrow-time seismic attributes and slices analysis, multi-provenances and distant braided delta depositional model has been concluded; (3) Based on source rock and caprock evaluation, with reservoir sands distribution and faults impact analysis on Yogou formation of Termit basin, structure-lithology, structure-strata, stratigraphic and lithology traps are concluded. Traps influencing factors, i.e., structure geometry, sands distribution, paleotopography, stratigraphy cycling, sand/shale lateral connection, reservoir quality and so on, have different impacts on these traps. Therefore, reservoir model of distant braided delta was established, and four lithology traps can be identified in center Fana uplift and southern Yogou slope of Termit basin.