258 ALEX. W. McCOY 



of the water to replace the oil is about 1,400 lbs. per square inch;^ 

 the unbalanced force due to specific gravity is less than o.i lb. 

 per inch; and frictional resistance is probably a fraction of a 

 pound per square inch. As the openings become larger the 

 capillary-expelling force of the water becomes less and when these 

 have reached o . 5 mm. this force is zero. Then the unbalanced 

 specific gravity and fractional resistance are the only forces to be 

 accounted for. Such places are only local in the sedimentary 

 series, and the great majority of openings in oil-bearing formations 

 are much smaller. The force necessary to make oil migrate 

 through a wet shale (openings o.oi micron) for a depth of 1,500 

 feet is about 4,000 lbs. per square inch. This is about 1,500 lbs. 

 per square inch greater than the combined rock and complete 

 hydrostatic pressure. Consequently, it is utterly useless to assume 

 migration of oil through wet shale. Even when the openings in a 

 sandstone are as much as o . i mm. in diameter, the capillary 

 resistive power is about 0.4 lb. per square inch compared with 

 o . I lb. per inch, the unbalanced force due to specific gravity. 

 The instant an oil particle (migrating in water sediments) reaches 

 a series of openings larger than those surrounding it, it stops and 

 remains there indefinitely, as long as these surrounding openings 

 are less than o.i mm. All sandstones are irregular and a series 

 of openings larger than o . i mm. is never very extensive. 



3. Experiment on migration of oil in wet sand. — A water-soaked (20-mesh) 

 sand bed with a 20° slope was placed in a glass box 18 in. by 6 in. by 6 in. 

 (Fig. 5). Near the lower end of the stratum a small volume of larger (10- 

 mesh) sand grains was filled with oil and covered with water-soaked shale. 

 This was allowed to remain for one week and no movement of the oil had 

 taken place. Then glass tubes were inserted into the sand at either end of 

 the box. Water was pumped out of tube No. i at the higher end of the 

 sand bed and at the same time water was allowed to run into tube No. 2 at 

 the lower end. This was continued until the amount of water forced 

 through the sand was several times its volume. No movement of the oil 

 resulted. The accompanying photograph, Fig. 6, was taken after the experi- 

 ment. 



'These figures are rough approximations from data of Johnston and Adams 

 (ibid.); also Harkins, Davies, and Clark, Journal American Chemical Society, XXXIX, 

 No. 4 (April, ,1917), 531. 



