High Precision Sequence Stratigraphic Analysis Of Single Well In Bohu Depression

Recent years,as the oil and gas exploration advanced in Bohu Depression,more and more difficulties appeared,the former sequence stratigraphy framework can't have a satisfactory result on high-precision stratigraphic contrasting in every tectonic units and can't meet the need on subtle reservior exploration. Therefore it is necessary to carry out high-precision stratigraphic analysis and research.First,the seismic sections which are representative in sedimentary features and structural features in Bohu Depression were selected.Eleven low frequency sequence surfaces were identified in Mesozoic Jurassic in Bohu Depression according to the identify signs of sequence surface on seismic sections.The Jurassic stratigraphy are divided into one first-grade sequence, three second-grade sequences, ten third-grade sequences by the above sequence surfaces.Then nineteen important exploration wells which are representative in sedimentary features in different regions of Bohu Depression were selected.According to the identify signs of high frequency sequence surfaces on the lithological profiles and the well log curves, the low frequency sequence units were identified and divided in third-grade sequence stratigraphy framework after the low frequency sequence units have being identified.And according to the identify signs of the first flooding surfaces and the maximum flooding surfaces,the system tracts were identified and divided,and the identification the single-well sedimentary facies and sedimentary subfacies and sedimentary microfacies were carrying out in the same time.In the end,the high precision sequence stratigrahpy framework with estimation function were founded in Mesozoic Jurassic in Bohu Depression.The sequence stratigrahpy framework is a mulriple half-graben structure.Each sequence set in Jurassic is constringent northward in South Sag and North Sag.The third-grade sequences in south of Bohu Depression are mostly truncated by the thrusting belt in Kuluketage and the boundary character is unconspicuous.At the same time, it is provided with the characteristics of the big continental depressional basin.The depositional slope-break belt is controled by the abrupt slope in Kuluketage in south of Bohu Depression, the gentle slope belt in north of Zhongmachang Salience and the abrupt slope belt in south of Zhongmachang Salience in middle part of Bohu Depression, the gentle slope belt in south of Yanqi Rise.The Jurassic sediments distribution is mostly along the quick subsidence centers in Bohu Depression. The Jurassic sediments of the lowstand system tracts are mostly distributed at the two quick subsidence centers comparted by Zhongmachang Salience.The sedimentary sources represent obviously difference in the east , in the middle and in the west,which lead to the distinct depositional system configuration and the movement of the primary sedimentary districts of the transgressive system tracts and the highstand system tracts and the sediment-subsidence centers.The difference of the sedimentary sequences and the system tracts in Jurassic are mainly controled by the synsedimental palaeouplifts and the palaeohighs and the quick subsidence centers in Bohu Depression.The sequence stratigraphy framework and the sequence mode are controled by the Zhongmachang Salience.The article supplies the geological foundation for the analysis on depositional system disposition and the subtle traps forcasting in Bohu Depression.