A Study Of Earth Tide Effects On The Hydrocarbon Migration

The earth tide is occurring repeatedly everyday. Many observations have proven that there is an earth tide effects on groundwater migration. Hydrocarbon is also a porous fluid which exists in rocks. Accordingly, there should be a tidal effects on the hydrocarbon migration as that on the groundwater. But till now, almost nobody has considered the earth tide effort in the researches of hydrocarbon migration. This article mainly discusses and analyses the earth tide effort on hydrocarbon migration, and whether we should take this effort into account as a kind of driving force.Different from oceans and lakes, the earth tide phenomenon is hard to detect. Under the effect of the tidal forces, the earth surface is going up and down with an amplitude of 35~40cm. During planetary conjunctions(such as solar and lunar eclipse), the amplitude can exceed 40 cm. There are two peaks(or valleys) on each day, but it doesn’t mean that the period of the earth tide is a half day. In fact, there are many tidal components, which can be divided into three classes: semi-diurnal tides, diurnal tides and long-term-ones.The mechanism of the earth tide effects on hydrocarbon migration can be summarized as following: the deformation of tidal force causes relevant hydraulic response. It changes the micro-structure of reservoir and disturbs the pressure distribution meanwhile. By theoretical analysis, this article finds the micro- mechanism and the macro-mechanism of the earth tide effects on hydrocarbon migration. On the micro-scale, it is proven that the pressure change caused by earth tide can provide a driving force that can help the oil puddles which nearly reach the critical condition pass the throat. On the macro-scale, using photomechanical analysis, the author concludes that, the pressure change disturbs the leakage field in the reservoir and shows an acceleration on the hydrocarbon migration. In order to investigate the scale of earth tide effort, the author builds up a model of fault system and calculates the influence on the migration rate and quantity by earth tide. By comparing them to the total migration rate and quantity, we obtain the trend and scale of earth tide effort on hydrocarbon migration.