Shale Lithofacies Characteristics And Development Rule Of The Lower Es₃ And Upper Es₄,Dongying Sag

Previous studies on shale are mainly focused on petrological and geochemical characteristics.With exploration and development of shale oil and gas,other aspects of shale research have also been launched.But research on shale lithofacies is relatively less,particularly in Dongying sag,because the exploration of shale oil and gas has just started.So characteristics and development rule of shale lithofacies was studied in the lower Es₃ and upper Es₄ in Dongying sag.Sequence stratigraphy was divided by synthesizing GRP sequence and element chemical sequence in the lower Es₃ and upper Es₄ of Dongying sag.Seven well sections and Sequence stratigraphic plane maps were worked out.There are eight sequences in research area.Sequence stratigraphy has several sedimentary centers on the plane,and sedimentary center also is stratum thickness center.Stratum thickness gradually increases from south to north and the rule of change has the vertical inheritance.Based on detailed description of core,thin sections identification,analysis of whole rock X-ray diffraction and geochemical test data,the primary characteristics of mineral composition,structure and organic matter abundance used as the basis for lithofacies classification were systematically analyzed and a shale lithofacies classification scheme was established.Meanwhile,the characteristics of main lithofacies types and distribution were studied.There are mainly four shale lithofacies,namely organic-rich lamina argillaceous limestone lithofacies,organic-rich stratiform argillaceous limestone lithofacies,organic-rich lamina lime mudstone and organic-rich stratiform lime mudstone lithofacies.Lithofacies characteristics and exploration practice demonstrates that the organic-rich lamina lithofacies is advantageous exploration target.The differences in mineral composition,organic matter abundance and well logging curve are shown to reflect the diverse sedimentary environment.Based on elements,paleontology and minerals,a method of sedimentary environment quantitative recovery was founded using factor analysis.Paleoclimate,paleosalinity,provenance,paleotopography,oxidation-reduction and water depth were recovered,and their classification standards were founded.By analyzing the influence factors of shale lithofacies on the sedimentary environment index,the mechanism of shale lithofacies formation was clear.Lithology is controlled by paleoclimate and paleotopography,sedimentary structure is controlled by paleotopography and water depth,organic matter abundance is controlled by paleoclimate and paleosalinity.In general,shale lithofacies are slightly more affected by paleoclimate and water depth,followed by paleotopography,followed by paleosalinity and oxidation-reduction,as a result of these five environmental factors.Under the control of sedimentary environment,there are four sedimentary facies sequences and three sedimentary modes of shale in the study area.Based on the data of mud logging,well logging and core,the identification model of mineral composition,TOC and sedimentary structure was established to identify shale lithofacies.The development rule of shale lithofacies was analyzed.The major types of shale lithofacies are basically distributed in sequence 1-8,but the main lithofacies are different and have certain inheritance.Influenced by the continental margin sedimentary system,shale lithofacies are symmetrically distributed in the section in the direction of perpendicular to sag long axis.Shale lithofacies are distributed in a ring shape in the plane,and the organic matter-lamellar lithofacies distribute in the geometric center of the sag.