油气充注成藏贡献度及其意义

油气成藏过程常伴随着多幕次的油气充注, 通过流体包裹体方法确定的油气成藏时期大都包含了一个油气藏形成过程中多幕次的油气充注.然而, 不是所有的充注幕次都对现今的油气藏具有贡献.因而确定哪一幕油气充注对现今油气成藏的贡献程度最大, 才是准确厘定油气成藏时期的前提.油包裹体是油气充注的直接证据, 当其他因素影响较小时, 油包裹体荧光颜色的改变反映的是其成熟度的变化, 也是其源岩热演化程度改变的响应.油包裹体成熟度可以通过已知油藏油的微束荧光光谱参数和原油API度关系来定量表征, 古油气成藏贡献度分析就是建立在油包裹体API度预测的基础上.在每一幕原油充注时期内, 成岩矿物捕获的油包裹体API度频率分布符合正态分布趋势, 理论上, 当有几幕原油充注时, 原油API度分布就存在几个正态分布趋势.通过对比油包裹体API度频率分布直方图与油藏现今流体API度, 可以比较出哪一幕原油充注对现今油气聚集的贡献度最大, 从而为油气成藏过程分析和油气充注PVTx(压力-体积-温度-组分)史恢复提供更好的约束条件. 

Contributions Degree of Petroleum Charging to Oil and Gas Accumulation and Its Significance

The petroleum accumulation always accompanies several petroleum charging episodes. The timing of petroleum accumulation determined by fluid inclusion method is usually representative of all the possible petroleum charging episodes, however, not all the petroleum charging episodes have contributions to present petroleum accumulation. Consequently, the premise for accurately determining the timing of petroleum accumulation is to confirm which petroleum charging episode has the most contribution to present petroleum accumulation. Petroleum inclusion is the direct evidence for petroleum migration and the variation of its fluorescent color reflects both of its maturity changing and the thermal evolvement level of its source rock if other influence factors have little effects on the oil maturity. The maturity of petroleum inclusion can be quantified by the relationship between the micro beam fluorescence spectrum parameters and API (American Petroleum Institute) degree of the known reservoir petroleum fluid. The analysis of contributions degree of petroleum charging to present petroleum accumulation is based on API degree prediction. The frequency distribution of API degree of petroleum inclusions should be a normal distribution in each petroleum charging episode. In theory, how many the episodes are, there are corresponding normal distributions of API degree of the petroleum inclusion. We can determine which episodic has the most contribution to the present petroleum accumulation by comparing the frequency distribution of API degree of petroleum inclusions with the API degree of present reservoir fluid, which can be a better restricted condition for the analysis of petroleum migration and accumulation and PVTx history of petroleum charging.