It has been observed in many places where oil and gas and water fill openings in porous beds enclosed in impervious ones, that gas rises above the oil and that the oil floats on water. Where the beds are arched to form a dome there is commonly a disc of gas surrounded by a circle of oil which is in turn surrounded by water. In some oil fields this gravitational arrangement is not clearly expressed, because the rocks are not fully saturated, or because the porous portions of the strata are spotted with impervious areas. The gravitational theory, because of the difficulties it has met in some fields, has appeared inadequate to many investigators, and elaborations and supporting theories have been proposed.

If, in a tube bent to represent an anticline, oil and water are charged with sand, the oil and water remain for months adhering tightly to the sand grains. There is no accumulation at the top of the tube and segregation is practically negligible. If, however, a small quantity of gas is introduced or generated in the tube, the oil and gas instantly begin to rise to the top of the fold, the gas rising above the oil and the oil floating on the water between sand grains. The separation is effected by a gas under pressure as low as four pounds to the square inch and some of the oil will move at least a foot per day.

Experiments have shown, however, that oil will move up a very low angle when gas is present under a few pounds of pressure. It will readily move up dips of one half degree and probably up dips considerably less when the pressure is high.

Experiments under various conditions with bent tubes appear to throw some little light on the manner in which oil accumulations are effected and gives indication of a probable cause of some of the tight, impervious spots in oil-bearing sands.

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