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.