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石炭系黄龙组岩溶岩是四川盆地东部渝北—邻水地区天然气藏最重要的储层之一,依据其结构特征,将该岩溶岩系划分为弱溶蚀岩溶岩、中等溶蚀多孔状岩溶岩、强溶蚀角砾状岩溶岩和强溶蚀交代次生灰质岩溶岩等4种类型,以及淡水方解石和白云石2种胶结物类型。对各类型样品的锶同位素分析结果表明:①不同成因类型、溶蚀强度、结构和成分特征的岩溶岩与胶结物锶同位素地球化学特征各异,其形成、演化与分布规律明显受古地理背景、流体性质和来源以及锶同位素分馏效应的控制;②岩溶过程中的87Sr/86Sr比值,具有从渗流—活跃潜流带的正偏移,至静滞潜流带逐渐转化为强烈负偏移演化趋势,对应的古岩溶储层物性由差变好至重新变差;③溶蚀过程中,白云质岩溶岩和淡水白云石胶结物对87Sr有很强的正偏移同位素分馏效应,而次生灰质岩溶岩和淡水方解石胶结物缺乏锶同位素分馏效应。
The Carboniferous Huanglong Formation karst rock is one of the most important reservoirs of natural gas reservoirs in the Yubei-Linshui area in the eastern Sichuan Basin. According to its structural features, the karst rock series are divided into weakly dissolved karst rock, moderately eroded porous karst rock, Strongly corroded brecciated karst rocks and strong dissolution secondary limestone karst rocks and other four kinds of types, as well as freshwater calcite and dolomite two cement types. The results of the strontium isotope analyzes of various types of samples show that: (1) the isotopic geochemical characteristics of strontium and karst rock with different genetic types, erosion intensity, structure and composition are different, and the formation, evolution and distribution of strontium are obviously influenced by paleogeographic background, Fluid properties and sources as well as the control of the strontium isotope fractionation; (2) The 87Sr / 86Sr ratio in karstification has a positive offset from seepage-active subsurface flow zone, Of paleokarst reservoirs changed from poor to bad again; ③ In the process of dissolution, dolomitic karst rocks and freshwater dolomite cements had a strong positive-offset isotopic fractionation effect on 87Sr, whereas secondary limestone karst and Freshwater calcite cements lack strontium isotope fractionation.