Yonxing Island-shidao Ankerite Dolomite In The Eastern Xisha Island Petrographic Characteristics And Its Spatial Variation

The South China Sea determines the broad prospects for oil and gas exploration in the South China Sea due to the special tectonic setting,the development of various types of reefs,and the combination of good reservoirs and reservoirs.The reef reservoirs in the oil producing areas of the South China Sea Basin also play an important role.Although the predecessors have done a lot of research on the genetic model and mechanism of the Xisha Islands dolomite,the research on the ankerite dolomite in the Xisha Islands is rare.Based on the study of the core data of Xike 1 well in Shidao and Xiyong 2 well in Yongxing Island of Xisha Islands,the analysis of the core rock and geochemical characteristics of the above core,Shidao Xike 1 well and Yongxing Island Xiyong 2 Systematic study on the genetic characteristics of well iron dolomite:Using x-ray powder diffraction quantitative analysis to determine eleven layers of ankerite dolomite in Shidao,and eight layers of ankerite dolomite in Yongxing Island Xiyong 2 well.The Xike 1 well and the Yongxing Island Xiyong 2 well ankerite dolomite are all developed,which are basically interbedded with dolomite and have obvious zoning.It is concluded by polarized light microscopy that the Miocene dolomite core in the Xiyong 2 well is dominated by bioclastic dolomite,and the dolomite crystals are powder-fine-grained;the ankerite dolomite content is higher in some layers,and the crystal is mainly microcrystalline-Powder crystal dolomite.Observing and analyzing the casting thin slices of Shike 1 in the Shidao 1 well,it is found that a large amount of clastic dolomite is developed in the Well of Xike 1 and the crystals are mostly fine-grain crystal structure,self-formed-semi-self-shaped,and some samples are black.Ankerite oxide or cement.For the scanning electron microscopy of the Shidaoxi 1 well and the Yongxing Island Xiyong 2 well,the dolomite crystals are observed to have a high degree of self-format ion,mainly belonging to the rhombohedral polyhedral structure and high degree of dolomification.According to the geochemical analysis of the Xike 1 well,the variation range of ? 13C and?18O in the Xike 1 well is consistent with the mixed water mode of action and is affected by long-term freshwater leaching.The main salt-forming oxides of carbonates in the West Branch 1 are mainly MgO,CaO and CO2,and the content is basically above 75%,CaO and MgO minerals have obvious segmentation characteristics in the drilling core,showing a significant negative correlation.The geochemical geochemical analysis of the Xiyong 2 well in Shidao District is considered to be dominated by CaO and MgO,and the FeO content of other samples is also high.Other chemical components are less,and MgO and CaO are negatively correlated.relationship.The content of Sr element indicates that it is in the mixed water environment of brackish water and has been subjected to long-term fresh water leaching.The Ni,Cu,and Zn elements are highly correlated with Fe,which is caused by the formation of heavy metal currents caused by the volcanic eruption of the high-point stone island.The study on the genetic model of the Yongxing Island and the 1 Shidao ankerite dolomite in the Xisha Islands suggests that the volcanic eruption of the high-point stone island,which is only 47 kilometers away from Yongxing Island,can form heavy metal currents,resulting in a large amount of ankerite-rich sol and other heavy metals.The enrichment of elements such as manganese,copper,zinc,chromium,nickel and cobalt,while heavy metals such as ankerite are affected by the prevailing winds in the two-way monsoon region of the South China Sea;the wind energy greatly increases the formation of high-energy wave transport and forms tidal currents.Or the wave flow,coupled with the prevailing wind in the bi-directional monsoon region,forms a dual-dynamic deposition effect,enabling the high-concentration Fe element sol to be transported to Yongxing Island and near Shidao and complete deposition,participating in the dolomitization process,and promoting Fe at high temperature.The exchange of three ions,Mg and Ca,causes Fe ions to enter the mineral lattice to form ankerite dolomite.Therefore,the genetic model of the ankerite dolomite in the Shikexike 1 well and the Yongxingdao Xiyong 2 well is the exchange of three ions of Fe,Mg and Ca,which promotes the formation of Fe ions into the mineral lattice to form ankerite dolomite and mixed water dolomitization.