612 



russell-dickey. POROSITY AND PERMEABILITY 



[Ch. 32 



where the mean pore radius diminishes. If the water wets the solid 

 surfaces, the oil cannot penetrate pores less than a certain size until 

 the pressure difference across the oil-water interface reaches a certain 

 amount. When this difference is attained by the addition of oil to 

 the column, the oil will penetrate the barrier and rise and accumulate 



2.7 

 2.6 

 2.5 



2.4 



</> 2.3 

 .32 



| 2.2 



<D 



>.2.1 



T3 



jo 2.0 



Ik 



1 1.9 



1.7 



1.6 

 1.5 

 1.4 



Present depth at Garber 

 o o o o o c 



Estimated maximum depth of burial in feet 

 Fig. 12. Change in density of Pennsylvanian and Permian shale with depth of 

 burial in Oklahoma. (After Athy, 1930, p. 12.) 



in the uppermost portion of continuous sand bodies. The height of 

 an oil column is seldom or never enough to give rise to a capillary pres- 

 sure sufficient to penetrate shales or shaly sands; therefore they act 

 as impermeable barriers. 



The migration of water as a result of compaction probably accounts 

 also for some of the phenomena of cementation. Anaerobic bacteria 

 that grow in bottom sediments obtain their oxygen from the reduction 

 of sulphates and produce carbon dioxide and hydrogen sulphide. These 

 gases, dissolved in the water, are probably effective in dissolving car- 

 bonate and silica and reprecipitating them in zones of lower pressure 

 and temperature. 



