Cretaceous sequence stratigraphic hierachies and the sedimentary response of sandy beach-bar in Ruman sag, Melut Basin, South Sudan
Chen Bin-Tao1, 2, Shi Zhong-Sheng1, Ma Feng-Liang1, He Wei-Wei1, Xue Luo1, Ma Lun1, Jia Yi-Rong1
1 Research Institute of Petroleum Exploration & Development-Northwest(NWGI),PetroChina,Lanzhou 730020,Gansu; 2 Key Laboratory of Reservoir Description,CNPC,Lanzhou 730020,Gansu;
Abstract：As a widely developed oil & gas reservoir in continental lake basin,lacustrine sandy beach-bar is an important target for lithological oil & gas reservoir exploration. Based on the identification and demarcation of sequence boundaries,palaeogeomorphic reconstruction,analysis of provenance system,sand-body distribution and reservoir-forming conditions,it can be found that the sequence evolution of the Cretaceous Gayger-Galhak Formations controlled the deposition of beach-bar in Ruman area,Melut Basin. Result shows that:(1) One 2nd-order sequence,three 3rd-order sequences(SQ1,SQ2 and SQ3)were developed in the target horizons,where SQ3 can be further divided into six Parasequence sets(corresponding to 4th-order sequences). (2)Different hierachies of sequences controlled the location and lateral distribution of sandy beach-bar,and reservoir-forming factors for lithological traps of beach-bar in different ways. The 2nd-order sequence controlled the vertical development position of beach-bar,where sand-bodies of beach-bar were mainly developed in the descending stage of relative base-level. The 3rd-order sequence controlled the lateral distribution of beach-bar,in the transit point between the descending and ascending semi-level of the 3rd-order sequence,beach bar developed around the Ruman burial hill,with large area(about 10km2),large thickness(10~20m)and high porosity(20%~25%). During the ascending stage of the 3rd-order sequence,subaqueous burial-hill platform deposition model was developed,with small area(1~4km2),thin thickness(2~3m)and relatively low porosity(15%~20%). The flooding surface of the 4th-order sequence controlled the distribution of sandy beach-bar reservoir-seal assemble,the flooding mudstone can be considered as local seal,determines the effectiveness of beach-bar lithological trap.
Chen Bin-Tao,Shi Zhong-Sheng,Ma Feng-Liang et al. Cretaceous sequence stratigraphic hierachies and the sedimentary response of sandy beach-bar in Ruman sag, Melut Basin, South Sudan[J]. JOPC, 2018, 20(6): 1013-1022.
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