The Study of Depositional System Characteristics of P Fm in GB Area on the Northern Slope in Bongor Basin

摘要

The GB area on the northern slope includes the BN sag and BC low uplift,where the great exploration breakthroughs have been found in P Fm and basement.The thickness of P Fm in the BN sag and BC low uplift and the lateral distribution of the reservoir sandbodies change quickly because of the complex structures activities.The lithological reservoirs have been found in the BN sag where a lot of research about the lithological reservoirs has been done.The BC low uplift was controlled by the Northwest-Southeast faults and appeared a triangle shape.There were multiple sub-sags due to the almost east-west faults in this area.It plays an important role to build the uniform sequence stratigraphy framework between the BN sag and the BC low uplift for predicting the distribution of the depositional system of the BC uplift.Synthesized the cores,logging and seismic data,a completion transgressive and regressive cycle of a third order sequence was found in the GB area which can be divided into four forth-order sequences i.e.,SQI,SQ1I,SQ1I1 and SQIV.SQI was the main exploration sequence and SQIV was an important potential sequence.The comprehensive study of the sedimentary facies showed that the small fan delta of near the source was the main depositional system and the braided channels/the front sand in middle fan/sheet sand/abyss-semi lacustrine facies were identified.Synthesized the structural characters,reservoir inversion and sandbody carving technology,5 independence fan delta sandbodies were identified in SQI in the BC low uplift area in the Northern Slope and No.1 and No.2 sandbodies had been explored while the No.3,No.4 and No.5 would be the most important sandbodies for the next exploration.