Objective：As a source reservoir symbiotic oil and gas accumulation, the research of shale oil reservoir is very important. Reservoir space (pores and fractures) is the core of shale reservoir research and has become a hot spot in unconventional oil and gas research in recent years. In recent years, with the development of shale oil exploration, the research on fine-grained sedimentation and shale reservoir has attracted more and more attention. Therefore, a genetic classification scheme for shale reservoir space in Dongying sag is established, the key geological mechanism controlling the development and evolution of reservoir space is clarified, and the genetic mechanism of main reservoir space types is discussed, The analysis of the effects of shale sedimentation and diagenesis on the formation, preservation and destruction of reservoir space has practical guiding significance for the optimization of favorable reservoir sections and shale oil and gas evaluation.
Methods: A study was controlled on the mud-shale development horizons of Es3^X and Es4^S in Paleogene Shahejie Formation, Dongying sag, Bohai Bay Basin. By means of X-ray diffraction whole rock mineral analysis, rock thin section and scanning electron microscopy, as well as major trace element test and organic geochemical test data, the basic characteristics of mud shale reservoirs were confirmed. Base on the identification of reserving space type and basic characteristic descriptions, the genetic classification scheme of reserving space in mud shale of Dongying sag was established: the critical geological mechanism affecting the development of reserving space was also deeply analyzed.

Results: The mud shale of Dongying sag is characterized by diversified architecture minerals and rock types, extremely strong reservoir heterogeneity, high abundance of organic matter (TOC is mainly ranged between 1.2% and 6.7%), low maturity (Ro value is dominantly in the range of 0.51%-0.89%), the porosity of 2.9%-9.8%, vertical permeability of 0.00340-0.578 mD and complex pore structure; (2) in terms of genesis and development abundance, the importance reserving space types include clay-mineral flocculent pores, clay-mineral contraction micro fissures, carbonate dissolution, composition fabric and plane distribution of pore framework mineral, and the lake salinization degree influenced by climate makes an impact on the vertical superimposed mixture mode of fine grains, so as to further control the types and assemblages of reserving space; in different salinization stages, the formation and evolution of secondary pores are controlled by the diagenetic fluid properties, changes of authigenic minerals such as carbonate and clay, as well as organic-matter hydrocarbon generation and evolution. Calcite recrystallization, clay mineral reaction and transformation, dissolution and organic-matter hydrocarbon generation function are important diagenesis types controlling the development of reserving space.

Conclusion: The diversity and complexity of shale oil reservoir space in Dongying sag are determined by the characteristics of shale reservoir structure, diversity of minerals and rock types, strong reservoir heterogeneity and low maturity in fault depression of lake basin. Clay mineral flocculation intergranular pores and intergranular shrinkage micro fractures, calcite and dolomite intergranular (internal) dissolution pores, calcite reconstituted intergranular pores, dolomitization intergranular pores, interlayer (micro) fractures and organic matter pores are the dominant reservoir types of shale oil in Dongying sag. The hydrocarbon generation and evolution of organic matter not only formed organic matter pores (fractures), but also participated in the development and evolution of almost all inorganic reservoir spaces. Sedimentary microfacies control the type and plane distribution of pore framework minerals. The climate and salinization degree of lake water medium in different sedimentary periods not only control the vertical superposition type of fine-grained materials, but also control the properties of diagenetic fluid, so as to further transform the reservoir space. In a certain salinity water environment in the late sedimentary stage of the Es4^S, fine-grained sediments are more sensitive to external reactions such as climate, and the types of rock facies and reservoir space are more diverse. The reaction and transformation of clay minerals, the recrystallization of calcite, the dissolution of feldspar and carbonate rocks, and the hydrocarbon generation and evolution of organic matter are the key geological processes controlling the formation and development of shale oil reservoir space. Calcite recrystallization and organic hydrocarbon generation evolution are the most typical representatives of the synergistic relationship between inorganic diagenesis and organic diagenesis of shale. The influence of the main diagenetic mechanisms on the formation and evolution of reservoir space is dynamic, and the pore increasing diagenesis and pore decreasing diagenesis are not strictly defined. The lithofacies with widely developed calcite recrystallization and dissolution in organic rich intervals are possible dominant lithofacies.
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Objective：As a source reservoir symbiotic oil and gas accumulation, the research of shale oil reservoir is very important. Reservoir space (pores and fractures) is the core of shale reservoir research and has become a hot spot in unconventional oil and gas research in recent years. In recent years, with the development of shale oil exploration, the research on fine-grained sedimentation and shale reservoir has attracted more and more attention. Therefore, a genetic classification scheme for shale reservoir space in Dongying sag is established, the key geological mechanism controlling the development and evolution of reservoir space is clarified, and the genetic mechanism of main reservoir space types is discussed, The analysis of the effects of shale sedimentation and diagenesis on the formation, preservation and destruction of reservoir space has practical guiding significance for the optimization of favorable reservoir sections and shale oil and gas evaluation.

Methods: A study was controlled on the mud-shale development horizons of Es3X and Es4S in Paleogene Shahejie Formation, Dongying sag, Bohai Bay Basin. By means of X-ray diffraction whole rock mineral analysis, rock thin section and scanning electron microscopy, as well as major trace element test and organic geochemical test data, the basic characteristics of mud shale reservoirs were confirmed. Base on the identification of reserving space type and basic characteristic descriptions, the genetic classification scheme of reserving space in mud shale of Dongying sag was established: the critical geological mechanism affecting the development of reserving space was also deeply analyzed.

Results: The mud shale of Dongying sag is characterized by diversified architecture minerals and rock types, extremely strong reservoir heterogeneity, high abundance of organic matter (TOC is mainly ranged between 1.2% and 6.7%), low maturity (Ro value is dominantly in the range of 0.51%-0.89%), the porosity of 2.9%-9.8%, vertical permeability of 0.00340-0.578 mD and complex pore structure; (2) in terms of genesis and development abundance, the importance reserving space types include clay-mineral flocculent pores, clay-mineral contraction micro fissures, carbonate dissolution, composition fabric and plane distribution of pore framework mineral, and the lake salinization degree influenced by climate makes an impact on the vertical superimposed mixture mode of fine grains, so as to further control the types and assemblages of reserving space; in different salinization stages, the formation and evolution of secondary pores are controlled by the diagenetic fluid properties, changes of authigenic minerals such as carbonate and clay, as well as organic-matter hydrocarbon generation and evolution. Calcite recrystallization, clay mineral reaction and transformation, dissolution and organic-matter hydrocarbon generation function are important diagenesis types controlling the development of reserving space.

Conclusion: The diversity and complexity of shale oil reservoir space in Dongying sag are determined by the characteristics of shale reservoir structure, diversity of minerals and rock types, strong reservoir heterogeneity and low maturity in fault depression of lake basin. Clay mineral flocculation intergranular pores and intergranular shrinkage micro fractures, calcite and dolomite intergranular (internal) dissolution pores, calcite reconstituted intergranular pores, dolomitization intergranular pores, interlayer (micro) fractures and organic matter pores are the dominant reservoir types of shale oil in Dongying sag. The hydrocarbon generation and evolution of organic matter not only formed organic matter pores (fractures), but also participated in the development and evolution of almost all inorganic reservoir spaces. Sedimentary microfacies control the type and plane distribution of pore framework minerals. The climate and salinization degree of lake water medium in different sedimentary periods not only control the vertical superposition type of fine-grained materials, but also control the properties of diagenetic fluid, so as to further transform the reservoir space. In a certain salinity water environment in the late sedimentary stage of the Es4S, fine-grained sediments are more sensitive to external reactions such as climate, and the types of rock facies and reservoir space are more diverse. The reaction and transformation of clay minerals, the recrystallization of calcite, the dissolution of feldspar and carbonate rocks, and the hydrocarbon generation and evolution of organic matter are the key geological processes controlling the formation and development of shale oil reservoir space. Calcite recrystallization and organic hydrocarbon generation evolution are the most typical representatives of the synergistic relationship between inorganic diagenesis and organic diagenesis of shale. The influence of the main diagenetic mechanisms on the formation and evolution of reservoir space is dynamic, and the pore increasing diagenesis and pore decreasing diagenesis are not strictly defined. The lithofacies with widely developed calcite recrystallization and dissolution in organic rich intervals are possible dominant lithofacies.​​​​​​​