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The AAPG/Datapages Combined Publications Database

Journal of Petroleum Geology


Journal of Petroleum Geology, Vol.3, No.3, pp. 325-331, 1981

┬ęCopyright 2000 Scientific Press, Ltd.


Kinji Magara**

* Approved for publication by the Director, Bureau of Economic Geology, The University of Texas at Austin.

** Bureau of Economic Geology, The University of Texas at Austin, Austin, Texas 78712, USA.


Difficulty of migrating a large amount of oil in either molecular or micellar solution may lead to an assumption that a continuous oil phase or a relatively high (20-30%) concentration of oil in pores of shales is necessary for primary migration to overcome the capillary restrictions against the oil. Movement of small oil globules in shales is believed by many workers to be an extremely difficult process. However, the above assumption is not necessarily valid in shales which contain a large quantity of structured and semi-solid water. Such oil globules may deform by the effect of compacting grains (solid material) and the semi-solid water, thus reducing the capillary restrictions significantly. This suggests that the small oil globules which are separated from each other can move in the direction of lower stress in the shales: a continuous oil phase or relatively high oil concentration is not a necessary requirement for primary oil migration.

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