High Resolution Seismic Attribute Analysis and Lithological Trap Identification of Thin Layer Braided River Delta Deposits: A Case on the Yogou and Sokor Formation in the Yogou 3-D Area of Agadem Block, Niger

Abstract

Abstract: Lithological trap identification is still a challenge for thin layer reservoirs in thick shales. Based on the high resolution sequence stratigraphy theory and seismic structure analysis, the high resolution sequence stratigraphy framework is established. With the sedimentary facies analysis of 22 wells in the nearly 2300km² Yogou 3D area, seismic sedimentary characteristics in the area are concluded. (1) Six kinds of sedimentary microfacies and three major reservoir sands are developed in late Cretaceous Yogou formation and early Paleogene Sokor formation. Submarine channels have a “bell” or “box” shape in GR, with a good continuity, strong to medium amplitude and medium frequency of seismic reflection with a flat top and convex bottom shape or a belt shape, and go thinner upwards; Mouth bars have a “funnel” shape in GR, with a bad continuity, weak to medium amplitude, low to medium frequency of seismic reflection with a convex top and flat bottom shape or an elongated shape, and go thicker upwards. They can be divided into channel (bar) trunks and channel (bar) flanks. Submarine sand sheets have a “finger” shape in GR, with a medium to good continuity, weak amplitude, medium to strong frequency of seismic reflection with a narrow belt shape and multi-periods suspension; (2) With the analysis of seismic sedimentary characteristics in reflection geometry shape, internal structure, amplitude, frequency and continuity, delta-front sands display quite different from shore, coast, prodelta deposits and volcanics; (3) Seismic amplitude extraction of 6 milliseconds' RMS in each zones of the YS3 sub-formation and sedimentary microfacies sands statistics in all wells show different source directions and planar sands distribution. (4) Considering about multi-grades fractures and the cap rocks later sealing, three sets of sands in the YS3 sub-formation can be correlated through the whole area. Most of oil beds are in the upper I and II sand sets of submarine channels and mouth bars onto the west slope and in the lower II and III sand sets of submarine sand sheets down to the east sag; (5) A mixed and distant source supply sedimentary model of this area is established. Key words: HRSS, seismic reflection, sedimentary characteristics, RMS, lithological trap

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