Geochemical Characteristics And Formation Mechanism Of Reservoir Of Lower Palaeozoic Burial Hills In The Regions Of Zhuangxi And Chengdao

In the last few years, we had obtained plenteous harvests on the exploration of lower Palaeozoic burial hills in the regions of Zhuangxi and Chengdao, Jiyang depression. With the enhancing of the exploration degree, it needs more deep research on its reservoirs to adapt to it. This thesis emphasizes to proceed the study on the mechanism of formation of the reservoirs of lower Palaeozoic burial hills in the regions of Zhuangxi and Chengdao from the angle of geochemistry.The research of petrology reveal rock types of the regions mainly include carbonate rock, claystone, siltstone, breccia and a few of evaporite rock. Among of them, carbonate rock is the primary type of them, it is the product of stable platform facies of marine.We study the geochemical characteristic of carbonate rock of lower Palaeozoic burial hills in the regions of Zhuangxi and Chengdao and find that the calcite fillings in cave or vein have high value of 87Sr/86Sr, low value of 13C and 18O and high Mn content among of different structural components. So it has been exposed to be dissolved by meteoric water on supcrgene diagenetic stage.We find that the petrology characteristic of all the samples have no characteristic of meteoric water such as geopetal structure, infiltrative sand, (uniform cement and gravitational cement on base of the research of the dolomite in the regions. On the dot diagram of combination of MgCO3(mol%) and Sr, the dot are all close to the line of seawater whether they are microlite-crystalline penecontemporaneous dolostone or diagenetic dolostone of various crystals. The 87Sr/86Sr value of dolostone or matrix is less than the one of sparry calcite in cave or vein, and close to the value of seawater. The 5 ' C and 8 ' O values of dolostone or matrix is greater than the ones of sparry calcite in cave or vein, but whose content of Mn is less than the ones of sparry calcite obviously. So we can draw a conclusion that the dolostone of C-O stratum in the regions of Zhuangxi and Chengdao has primarily two genesis types, they are penecontemporaneous dolostone and diagenetic dolostone. The diagenetic dolostone is formed by replacement in intergranular pore water on the course of burial diagenesis. The reservoir of dolomite is mainly distributed in diagenetic dolostone. So the formation mechanism of diagenetic dolostone have directly relation with that ofthe reservoir pore. The formation mechanism of the pore of diagenetic dolostone includes: 1) The primary porosity is essential condition for the formation of dolostone reservoir. A lot of diagenetic dolostones have remainder granulation structure, and the native rock of it may be various intraclast limestone. This type of rock usually has high primary porosity. The high primary porosity is the important base of forming the pore of dolostone reservoir. 2) The contraction action of granulations can form the pore of dolostone reservoir in the course of dolomitization.Huge deep fractures in the east of China have a little influence on the pore of carbonatite reservoir of €-O stratum in the regions of Zhuangxi and Chengdao. The karstification which probably happened at Xishan tectogenesis period is also very limited.