莺歌海盆地乐东区碳酸盐胶结物成因及地质意义

Origin of Carbonate Cement in Reservoirs of Ledong Area,Yinggehai Basin and Its Geological Significance

为探讨乐东区碳酸盐胶结物的分布规律、成因机制及其对储层质量的影响,应用铸体薄片、碳氧同位素、包裹体对碳酸盐胶结物岩石学、地球化学等特征进行综合分析.研究结果表明,从斜坡带往凹陷中心,碳酸盐含量由18.0%降至5.0%;其δ13C值分布在-4.78‰^+1.03‰,δ18O值分布在-10.99‰^-6.34‰,Z值分布在111.27~123.59,古海水温度分布在11.36~32.02℃,古盐度分布在3.24%~6.91%;碳酸盐胶结物的形成主要与碳酸盐岩或高钙质砂岩母岩的溶解再沉淀有关,其受控于水介质温度、成岩温度与盐度,由斜坡带往凹陷中心,水介质温度降低、盐度增高,胶结变弱.低含量的早期(铁)方解石与高温热流体溶解高含量早期(铁)方解产生的低或高含量的晚期(铁)白云石区均可发育中渗'甜点'储层.

In order to explore the distribution law,formation mechanism and its effect on reservoir quality in Ledong District,a comprehensive study of petrology and geochemistry was carried out on the characteristics of cast thin sections,carbon and oxygen isotopes,and inclusions of carbonate cement.The results show that the carbonate cement content from the slope to the depression center has been reduced from 18.0%to 5.0%,and itsδ13 C value is distributed in the range of-4.78‰^+1.03‰,theδ18 O value is distributed in the range of-10.99‰to-6.34‰,Z Values range from 111.27 to 123.59,ancient sea water temperature is distributed in the range of 11.36℃to 32.02℃,ancient salinity is distributed in the range of 3.24%to 6.91%.It is found that the formation of carbonate cement is mainly related to the dissolution and precipitation of carbonate rock or high calcareous sandstone,which is controlled by the water medium temperature,the formation temperature and salinity.From the slope to the depression center,the water medium temperature is reduced,the salinity is increased,and the bond is weak.Low-content early(iron)calcite and high temperature hot fluid dissolved early(iron)calcite produced by low or high content of late(iron)dolomite areas can develop medium-permeability'sweet spot'reservoirs.