珠江口盆地文昌A凹陷珠海组储层碳酸盐胶结物分布规律及成因机制

Distribution and genetic mechanism of carbonate cements in the Zhuhai Formation reservoirs in Wenchang-A sag,Pear River Mouth Basin

运用沉积矿物学和岩石学等方法,并结合碳氧同位素和电子探针等分析手段,分析了珠江口盆地文昌A凹陷珠海组碳酸盐胶结物的分布规律、形成环境和物质来源。研究表明,碳酸盐胶结物对珠海组储层物性影响明显。当碳酸盐胶结物含量大于5%时,储层物性随其含量增加明显降低。砂岩薄片鉴定结果显示,珠海组储层碳酸盐胶结物的含量和类型横、纵向呈明显规律分布。胶结物含量珠海组一段和二段高于三段,南断裂带高于凹陷中心。胶结物类型以中期铁方解石和晚期铁白云石胶结为主,发育部分菱铁矿和白云石,局部发育早期连晶方解石。碳酸盐胶结物的形成与有机酸脱羧作用有关,且一定程度受淡水影响明显,其物质来源表现为长石的溶解和粘土矿物的转化为其形成提供丰富的钙来源,钙质有孔虫的溶解也是其形成的物质基础。

Sedimentary mineralogical and petrological methods in combination with oxygen-carbon isotope and electron probe were used to analyze the distribution,forming environment and material sources of the carbonate cements in the Zhuhai Formation in Wenchang A sag,Pear River Mouth Basin.The result indicates that the carbonate cements significantly affect reservoir quality.When the content of carbonate cements is greater than 5%,the reservoir quality significantly deteriorates.Furthermore,the distribution of carbonate cements show obvious regularity both vertically and horizontally.The content of carbonate cements in the 1st and 2nd members of Zhuhai Formation are higher than that of the 3rd member,and it is higher in the southern fault zone than the center of the sag.The carbonate cements are dominated by middle ferric calcite and late ferric dolomite,followed by siderite and dolomite as well as local early crystal stock calcite.The forming of carbonate cements is resulted from decarboxylation of organic acid and influenced obviously by freshwater.In addition to dissolution of calcareous foraminifer,feldspar dissolution and clay mineral transformation provide abundant calcium for the carbonate cements development.