Changes Of Oil/gas Saturation In Hydrocarbon Migration And Accumulation

By means of simulation test and such data as geology and geochemistry, the variety of oil saturation is investigated in course of hydrocarbon accumulation from dynamics angle, The paper has obtained mainly many productions and acknowledges as follows:1. The correlation between variety of oil saturation and migration force and resistance is close in course of hydrocarbon accumulation.(1) The migration force of oil is bigger than that of water and increases constantly during the source of compaction of water-wet sandy and argillaceous sediment. So water is discharged during the source of compaction of oil-water bearing sediment. It makes oil saturation increase gradually.(2) During the course of decompression, the compressibility and expandability of gas, oil and water are key factors of the variety of oil saturation. Due to big expansion coefficient of gas, gas is given priority to expansion and takes oil away, which makes oil saturation decrease and gas saturation increase accordingly.(3) When oil enters the hole of water-wet sandstone driven by pressure difference, oil migrates following a line of less resistance because of the migration force of oil is bigger than that of water. With the ceaseless injection of oil and the migration passage prolonging, the result is that migration force increases and oil comes into little hole near charging point.(4) The qualification of making oil float on the sandstone is having continuous oil phase volume. Driven by buoyancy, oil usually migrates along the little resistance hole. As a result, the limited migration passages are formed. The oil ascent process is the process of oil migrating to upward direction. That is the oil saturation is high in the upward direction and low in the downward direction accordingly.2. Oil saturation in source rocks enhances with the increasing buried depth and the intense compaction. The release of pressure resulting from the denudation and faults can seduce the expansion of gas and migration of oil. Ultimately, the oil saturation reduces.3. The variety of oil saturation has close relation with injection manner of oil. Compaction, decompression and buoyancy are also influencing it to a certain extent.Commonly, hydrocarbon in source rocks infused reservoir and the nearer charging point, the higher oil saturation under the action of pressure difference. In reservoir contacting with source rocks directly, the oil saturation rises in the neighborhood of source rocks. In reservoir separated from source rocks, oil fills in faults and fractures jointing source rocks and reservoirs firstly, next in reservoirs.Compaction makes oil saturation in reservoir enhanced. On the contrary, decompression can leads it deduce. When oil phase enrich to a certain degree, the buoyancy can promote oil to migrate upward slope and make oil saturation augment in upward direction.4. Oil saturation increases with the augment of buried depth in the upper part of the forth section and middle-lower part of the third section of Shahejie Formation in Liangjialou oil field of Dongying Sag. Oil formation of the second section and the upper part of the third section of Shahejie Formation is controlled by source faults. Moreover, oil enriches in the upward direction mainly. It is a living example for the variety and distribution of oil saturation in source rocks and reservoirs.