油气垂向微运移的证据及特点

烃类垂向运移是一个复杂的地质-地球化学过程,严格受边界条件控制,在地质历史上具有一定的阶段性。水文地球化学指标表明:地下水矿化度的梯度变化及离子组合改变等都因油气垂向微运移所致。油气垂向微运移还使得轻烃组分、芳烃荧光强度发生规律性的变化:从储层到盖层,分子量和分子半径小的轻烃相对富集,不同波长段的芳烃荧光强度显著降低。另外,深部油气藏与地表的甲烷碳同位素值基本一致,也说明了油气的确存在垂向微运移。因油气垂向微运移具有阶段性和间歇性等特点,所以在化探指标柱状图上,地化指标常出现多个由高→低或由低→高的旋回。

EVIDENCE AND CHARACTERISTICS OF OIL AND GAS VERTICAL MICRO-MIGRATION

Hydrocarbon vertical micro migration is a complicated geological geochemical process.It is strictly controlled by boundary condition,possesses stages in geological history.The mineralization degree of ground water shows gradient variation and ionic combinatiom changes due to the action of ground water and hydrocarbon during the vertical micro migration.Hydrocarbon vertical micro migration can change the ion combination,causes regular variation in component of light hydrocarbons and the fluorescent intensity of aromatic hydrocarbons.That is to say,light hydrocarbons with small molecular weight and small radius relatively increases from reservoir to the caprocks,but the fluorescent intensity of aromatic hydrocarbon decreases distinctly,and the carbon isotopic value of methane of both deep seated reservoir and groud surface are basically the same.Since hydrocarbon vertical miero migration is periodical and intermittent,the geochemical index usually in cycles from high to low or from low to high on geochemical exploration index colunm.