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鄂尔多斯盆地米脂气田南侧断裂带充填的方解石脉富含天然气包裹体.应用流体包裹体测试、稳定同位素分析和热释光年龄测定等手段,研究了方解石脉和天然气包裹体成因特征及其形成时间.分析表明,天然气包裹体形成温度在130～140℃之间,盐度为5.5(质量百分比)NaCl～6.0(质量百分比)NaCl,表明天然气包裹体属于盆地内热成因烃类流体.热爆法分析方解石脉包裹体烃类气体含量最高达2.4219m3/t,C1/ΣCi比值最高为91%.激光拉曼光谱分析的单个包裹体中烃类气体最高含量为91.6%.方解石脉δ13CPDB为-5.75‰～-15.23‰,δ18OSMOW为21.33‰～21.67‰,表明断裂带中含天然气包裹体方解石脉属于淡水成因方解石.天然气包裹体δ13C1PDB为-21.36‰～-29.06‰,δDSMOW为-70.89‰～-111.03‰,其与米脂气田同属于煤成天然气.含天然气包裹体的方解石脉热释光年龄为32.4±34.2万年.综合研究认为,晚期断裂构造活动对天然气成藏具有重要影响,米脂气田南侧断裂带方解石脉天然气包裹体是米脂气藏受喜马拉雅构造活动影响,天然气沿断裂发生逸散的证据.
The calcite veins filled south of the Mizhi gas field in the Ordos Basin are rich in gas inclusions. The fluid inclusions, stable isotope analysis and thermoluminescence dating were used to study the genetic characteristics and formation of calcite veins and natural gas inclusions Time.The analysis shows that the formation temperature of natural gas inclusions is between 130 and 140 ℃ and the salinity is 5.5% NaCl NaCl 6.0%, indicating that natural gas inclusions belong to the thermal hydrocarbon fluid in the basin.The thermal explosion method The hydrocarbon gas content in the calcite inclusion is up to 2.4219m3 / t and the ratio of C1 / ΣCi is up to 91%. The highest content of hydrocarbon gas in single inclusions by laser Raman spectroscopy is 91.6% .The δ13CPDB of calcite vein is -5.75 ‰ ~ -15.23 ‰ and δ18OSMOW are 21.33 ‰ ~ 21.67 ‰, indicating that the calcite veins of gas inclusions in natural gas inclusions belonged to freshwater-forming calcite.The δ13C1PDB of natural gas inclusions ranged from -21.36 ‰ to -29.06 ‰ and δDSMOW from -70.89 ‰ to -111.03 ‰, which belongs to the same natural gas as Mizhi gas field.The caloric age of calcite veins containing natural gas inclusions is 32.4 ± 342,000 years.A comprehensive study shows that the late faults Tibetan tectonic activity has an important influence on the natural gas, gas Mizhi south fault calcite vein gas inclusions MIZHI gas reservoir is affected Himalaya tectonic activity, evidence of fracture along the escaping gas.