鄂尔多斯盆地宜川-旬邑地区长8储集层碳酸盐胶结物特征

Characteristics of carbonate cements of Member 8 of Yanchang Formation in the Yichuan-Xunyi area,Ordos Basin,China

鄂尔多斯盆地延长组储层质量严重地受碳酸盐胶结物影响。通过对宜川-旬邑地区长8储集层薄片、碳酸盐胶结物碳氧同位素及流体包裹体测试分析,表明碳酸盐胶结物主要是铁方解石（含铁方解石）,在薄层砂岩中和厚层砂岩顶底与泥岩紧密毗邻的区域含量较高,以中细晶及粗-巨晶颗粒充填孔隙。碳酸盐胶结物δ13CPDB值为-5.56‰~0.22‰,δ18OPDB值为-10.58‰~21.47‰,流体包裹体均一温度在58~121℃之间。温度峰值区间为100~110℃之间。成因分析表明该区碳酸盐胶结物来源主要与有机质及黏土矿物演化有关,形成时代较晚。碳酸盐胶结物大量发育对储层物性具有严重的负作用。

The reservoir quality of Upper Triassic Yanchang Formation in Ordos Basin is seriously affected by the carbonate cements.The thin sections are analysed,and the carbon and oxygen isotopes of carbonate cements and fluid inclusions are tested.The study results indicate that the carbonate cements of Member 8 of Yanchang Formation reservoir on the south-east edge of Ordos Basin are mainly iron carbonate cements calcite（ferrous calcite） cementation,which exist on the thin sandstone and thick sandstone to nearly mudstone.The carbonate cements fill pores with fine-grained and coarse-giant crystal particles.The test analysis results of the carbon and oxygen isotopes of the carbonate cements and fluid inclusions show that δ13CPDB value is-5.56‰～-0.22‰,and δ18OPDB-10.58‰～-21.47‰,that the fluid inclusion homogenization temperature is 58～121℃,and the main temperature ranges from 100～110 ℃.The genesis analysis of the carbonate cements show that the main source of carbonate cement materials is related to the evolution of organic matter and clay minerals formed in a relatively later era.The development of a large number of carbonate cements has serious negative effects on the reservoir properties.