Research On Diagenetic Evolution-hydrocarbon Filling Process Of The Late Oligocene-the Early Miocene Sandstone Reservoir In The Baiyun Deepwater Area

The deepwater area in the Shelf of northern south China sea has good petroleum geological condition and accumulation conditions. Baiyun sag is the most representative Cenozoic Depositional district of the deep slope area in the northern south China sea. It is detailed and single that aim at the research of the period of oil and gas filling and diagenesis of sandstone reservoir before, But, the process of Diagenetic evolution-hydrocarbon filling, Evolution of diagenetic fluid conditions and the effect on porosity evolution of Diagenetic-hydrocarbon filling process is still weak-welled in the Baiyun deepwater area. In this paper,we used the identification and quantitative statistics of the conventional thin section and casting thin section under microscope, observation by scanning electron microscope, analysis of electron microprobe analysis, image pore throat analysis, X-ray diffraction analysis, composition analysis of laser Raman probes containing hydrocarbon inclusions, analysis of organic inclusion body fluorescence characteristics and homogeneous temperature measurement and other methods of analysis and testing. After the systematic study of sandstone petrologic characterization, physical characteristics, main diagenesis types, hydrocarbon charging period, diagenetic, hydrocarbon filling sequence and evolutive features of diagenetic fluid of Baiyun Sag in the late Oligocene Zhuhai formation-Early Miocene Zhujiang Formation, we established the relationship among diagenetic, hydrocarbon filling and pore evolution, discussed the difference of diagenesis of sandstone reservoirs in Zhuhai formation and Zhujiang Formationand the influence on reservoir properties.Studies have shown that the reservoir sandstone types of Baiyun Sag in the early Miocene Zhujiang Formation, late Oligocene Zhuhai formation are basically identical,mainly consisting of detritus feldspar sandstone and feldspar detritus sandstone,partly consisting of feldspar quartzite sandstone, lithic quartzite sandstone and feldspar sandstone.The sandstone reservoirs in the Zhujiang formation are generally in the A phase of the middle diagenetic stage.The sandstone reservoirs in the Zhuhai formation are generally in the A-B phase of the middle diagenetic stage.The main diagenesis types of the sandstone reservoirs in Zhuhai Formation and the Zhujiang Formation are basically the same.but,there are some differences in the strength of diagenesis.The sandstone reservoirs in the Zhujiang formation are enrich in the early-stage carbonate cementation and have a certain resistance to compaction,while the early carbonate cementation was not developed in the Zhuhai formation.the sandstone compaction of Zhuhai formation is stronger than that of the Zhujiang formation,the reduction of porosity of Zhuhai formation is mainly caused by compaction.(the peak area of pore loss is 20%-38.3%, accounting for 71.4% of total compacted pore loss) Kaolinite, quartz, calcite and dolomite are the main cements in the late diagenetic stage of Zhuhai formation and the Zhujiang formation,but the development of late carbonate cements in the Zhuhai Formation was stronger than that in the Zhujiang Formation,meanwhile,the transformation of kaolinite to illite is obvious and the reduction of porosity (the peak area of pore loss is 25%-37%%, accounting for the total loss of the total pore volume of the 14.3%)is higher than sandstone reservoirs in Zhuhai Formation which is mainly caused by cementation.(the loss of the peak area is25%-35%, which accounts for 5% of the total loss of cemented pores) the dissolution improved the physical properties of sandstone reservoirs in the two groups to a certain extent.yet the dissolution degree of minerals in the Zhujiang formation is clear stronger than sandstone of Zhuhai formation,resulting in the rate of enhanced hole of sandstone reservoir in the Zhujiang (the increasing peak area is 6%-16%, which accounts for 50% of the total increase in the hole)formation caused by dissolution is higher than that of Zhuhai formation.(the increasing peak area is 2%-8%, accounting for the total amount of increase of 51.4%) The image pore throat analysis indicate that the size of sandstone in the Zhujiang is 30.72?m-216.16?m,throat width is 5.48?m-24.04?m and has good connectedness between porous and throat.The size of sandstone in the Zhuhai is 44.33?m-157.27?m,throat width is 3.11?m-16.2?m and has poor connectedness between porous and throat.The physical properties and reservoir properties of sandstone reservoirs are worse than that of the Zhujiang Formation.The diagenetic sequence and the characteristics of fluid inclusions disclose that the sandstone reservoir of the Zhujiang formation and the Zhuhai formation experienced three-four oil and gas filling process.the second phase and the third phase is larger than others among those phases.The diagenetic fluid medium of the sandstone reservoir has experienced 4 stages:early alkaline and alkaline,medium acidity, late basic, late-today weak acidity.The research results are help to correctly understand the mechanism of the effect of diagenesis on the reservoir diagenesis of deepwater sedimentary sandstone,discuss the evolution mechanism of fluid rock interaction controlled by the dynamic process of hydrocarbon filling and diagenetic,and guide the practice of oil and gas exploration and development.