EFFECTS OF CAPILLARITY ON OIL ACCUMULATION 801 



secondly, that above 750 m. capillary pressure in openings of 0.01 

 micron is greater than the combined rock and hydrostatic pres- 

 sures; therefore capillarity is most important in the upper 3,000 ft. 

 of the earth's crust; and thirdly, that above 5,000 ft. one liquid of 

 greater surface tension and adhesion for the tube material should 

 readily replace a weaker liquid in small openings; or in other words, 

 the liquid of less surface tension should be concentrated in the 

 larger openings. 



CAPILLARY PRESSURES UNDER VARYING CONDITIONS* 



* Johnston and Adams, op. cit., XXII, 13. 



t An increase of temperature of i" for every 30 m. was used to obtain these results. 



Capillary phenomena can take place in openings of o . 01 micron, 

 as shown by Bakker, 1 where he concludes that the minimum size 

 of capillary openings is a few times the diameter of the molecule. 

 According to Whitney, 2 mud contains more than 10,000,000,000 

 particles per gram. If these were perfectly round particles, so 

 that the pore space could be a maximum, the diameter of the 

 individual would be about 3 microns. Therefore the maximum 

 openings would be about o . 5 micron. Clay used in the following 

 experiments was made up of particles which varied from 1 to 5 

 microns in diameter, as measured by a microscope. The openings 

 then at a maximum would be a fraction of a micron. Now, since 

 the openings in mud are evidently less than 1 micron by both of the 

 above methods of approach, it has been assumed for the following 

 hypothetical problem, that in compressed shales where the particles 

 are not round nor of equal size the openings are diminished to 

 0.01 micron. 



1 Zeitschrift fur physikalische Chemie, LXXX, No. 2, 129. 



2 U.S. Dept. Ag., Weather Bureau, Bull. 4, p. 73. 



