碳酸盐岩碳、氧同位素分析激光微取样技术

碳酸盐岩碳、氧同位素分析激光微取样技术是利用高能聚焦激光束与碳酸盐岩样品作用,热分解产生CO₂气体,经真空提纯净化后送质谱仪分析测定其C、O同位素值。其空间分辨率优于20μm,能有效地对碳酸盐岩各细微组分结构分别取样,以满足同位素地质学研究的需要。经标样测定,δ¹³C和δ¹⁸O的最好分析精度可达±0.22‰(σ),与常规磷酸分解法分析精度相;δ¹³C无明显分馏现象,δ¹⁸O分馏明显,但对同种矿物是一个常量(方解石偏负1.72‰;白云石偏负1.59‰)易于校正。激光微取样主要应用于碳酸盐储集岩样品碳、氧同位素分析,能较好地解释油气储层孔隙演化和成岩过程。

THE LASER MICRO-SAMPLING TECHNIQUE FOR ANALYSIS OF C AND O ISOTOPE IN CARBONATE

The process of laser micro-sampling for analysis of C and O isotope in carbonate minerals is to focus a high-power laser beam on a carbonate sample to liberate CO2gas. Then the CO2gas is purified and sent into a mass spectrometer for isotope analysis of C and O, and its spatial resolution rate is more than 20μm. It is an effective way of separately producing CO2gas from all kinds of fine structure composition in carbonate to meet the need of isotope geology studies. Fractionation and reproducibility are characterized by analyzing carbonate standards: the optimal precision is approximately±0.22‰(σ) for bothδ¹³C and δ¹⁸O incarbonate standards, which is the same as what is gained in conventional acid dissolution method;δ13C is not evident in fractionation during laser micro-sampling, whileδ18O is. Thisprecision is constant (calcite,-1.72‰;dolomite,-1.59‰) for the same mineral and it can thus easily be corrected . The laser micro-sampling has been mainly used to analyze the isotopes of C and O in carbonate reservoir rocks and the isotope values. Meanwhile it can well explain the diagenesis process and porosity evolution of container rock.