长岭断陷火山岩储层内碳酸盐矿物碳氧同位素组成及其成因

Carbon and Oxygen Isotopic Compositions and Genesis of Carbonate Minerals in a Volcanic Reservoir from the Changling Rift

碳酸盐矿物是火山岩储层内重要的矿物成分,长岭断陷火山岩储层内的自生碳酸盐矿物主要是方解石。本文通过对营城组储层内方解石矿物的碳氧同位素特征分析,探讨储层内碳酸盐矿物成因。研究表明,长岭断陷火山岩储层内方解石δ13 CV-PDB值范围为-12.7‰～0.4‰,δ18 OV-SMOW值范围为3.8‰～12‰,具有高δ18 O值。与方解石平衡的CO2碳同位素计算值范围较宽,为-16.0‰～2.2‰,表明其形成物质的多源性。在δ18 O-δ13 C图解中显示,形成碳酸盐矿物的CO2来源于幔源-岩浆无机成因的CO2和有机质演化过程中产生的CO2,以无机成因CO2源为主。这些无机成因CO2、有机成因CO2和沉积有机质热演化产生的有机酸溶于流体,形成酸性流体。火山岩储层中碳酸盐矿物的形成实质就是这种酸性流体与储层围岩反应的结果。

Carbonate mineral is an important mineral component in the YingCheng formation volcanic reservoir of the Changling rift,and calcite is the main authigenic carbonate mineral.On the basis of isotopic analyses of C and O in the calcite,the genesis of authigenic carbonate mineral in this volcanic reservoir was studied.The results show that the δ13C V-PDB values of calcite in samples collected from the volcanic reservoir of the Changling rift range from-12.7‰ to 0.4‰;that these samples are characterized by high δ18O values of from 3.8‰ to 12‰;and that the calculated δ13C values of CO2 gas equilibrium with calcite range from-16.0‰ to 2.2‰.The large variation of carbon and oxygen isotope compositions indicates that mineral-forming material may derive from multiple sources.The δ13C-δ18O diagram of calcite suggests that the calcite-forming CO2 gas originated from both inorganic and organic sources,mantle and magma are major sources and sedimentary organic matter is the secondary source.The inorganic and organic CO2 gases and organic acids produced by the thermal evolution of organic matter dissolved in the fluid to form an acidic fluid.Finally,this fluid reacted with silicate mineral in the volcanic reservoir to form carbonate mineral.