The Lithofacies And Its Development Characteristics Of Fine-grained Sedimentary Rocks In Es3x- Es4s Sub Member Of Dongying Sag

Lacustrine deep-water fine-grained sedimentary rocks contain abundant unconventional oil and gas resources.But because of complicated mineral composition and unusually rich types of laminated of fine-grained sedimentary rocks,the current academic circles have not yet established a comprehensive and system lithofacies classification scheme.And the vertical heterogeneity of lithofacies is extremely strong,so the development characteristics of lithofacies are unclear.These factors seriously restricted the shale oil and gas exploration.So we carried out this study.Combined with spectral analysis and wavelet analysis method,the earth's orbital parameters were systematically analyzed.The research results show that the difference of orbital periods in theory between Es4 s and Es3 x is small.The cycle ratio of precession,obliquity,short eccentricity and long eccentricity is 1: 2: 5: 20.Then the natural gamma-ray logging data of system cored wells also were systematically analyzed using the same method.There are four long eccentricity cycles both of Es4 s and Es3 x.The accumulation rate of lacustrine deep-water fine-grained sedimentary rocks is estimated as 66.2~278.5 ?m/a,that indicates the lamina couplet of lamellar lithofacies were formed in a year and controlled by the four seasons climate change.Using Milankovitch cycles can realize stratigraphic correlation between system cored wells.Combining detailed description of core,thin sections identification,analysis of whole rock X-ray diffraction,scanning electron microscopy and electron back scattered diffraction technologies,the characteristics of mineral composition,sedimentary structure,laminations and geochemical of lacustrine deep-water fine-grained sedimentary rocks in the Es4 s and Es3 x in the Dongying sag were described in detail.Based on the detailed description of petrologic feature,this study sets up a lithofacies classification scheme that is suitable for the fine-grained sedimentary rock in the Es4 s and Es3 x in the Dongying sag.The analyses are based on the direct reflection of lithofacies differences and integrating various factors such as mineral composition,sedimentary structure,organic matter abundance.Then the characteristics and development environment of main lithofacies are analyzed.Based on the study of sedimentary environmental elements and lithofacies elements,including mineral composition?sedimentary structure and organic matter,the lithofacies association and distributing characteristics of high quality lithofacies were studied.There are four types lithofacies association in the Milankovitch cycles stratigraphic framework.And the cyclicity change of lithofacies association mainly controlled by precession.The long eccentricity cycle 2 and 3 are the the best interval of shale oil on account of optimal ratio of lithofacies elements.The corresponding characteristics of different rocks are obvious,according to that the logging model was established.Then,The distribution characteristics of high quality lithofacies were analyzed.The results indicate that high quality lithofacies are mainly distributed in the Boxing subsag?the Niuzhuang subsag and the central structural belt.