178 I. C. WHITE HISTORY OF PETROLEUM AND NATURAL GAS 



in ever}^ oil and gas field. By means of these experiments he not only 

 demonstrated the overwhelming preponderance of gravity as the prin- 

 cipal factor in oil and gas accumulation, but proved the minor part 

 played by capillarity. The "Anticlinal," or gravitational, theory for 

 oil and gas segregation into valuable pools having always been insisted 

 on by your speaker as the main and controlling factor, it is with con- 

 siderable satisfaction that, after many assaults by able but mistaken 

 geologists, the buoyancy theory has been so signally sustained through 

 these exhaustive and demonstrative experiments of Mr. Mills, whose 

 results are briefly set forth in his concluding summary as follows: 



Summary of E. Van A. Mills' Eesults 



"To enumerate the various relationships indicated by the investigations 

 lierein described would require a longer paper than is appropriate at this 

 time. Consequently, in addition to the conclusions from the experiments, the 

 present contribution is summarized by a statement of a few of the broad facts 

 and relationships that have been established. 



"One of the most important things to be realized is that all of the phenomena 

 observed in the laboratory, as well as in the field, are brought about through 

 the influence of various factors with different eftects. In other words, we are 

 obliged to deal with the summation of the effects of many factors, not with 

 the effect of any single factor. The values of the different factors that 

 influence the migration, accumulation, mode of occurrence, and the recovery of 

 oil and gas are extremely variable and are illative one to another. Different 

 factors have predominating influences according to the different sets of limit- 

 ing conditions into which enter, collectively, the porosities, fineness of pores, 

 textural variations, and degrees of dip of the sands, the qualities of the fluids, 

 more especially the viscosities of the oils, the degrees of saturation of the 

 strata by water and oil, the temperatures, pressures, and many other con- 

 ditions. Thus, it is recognized that there is a wide range of variation in the 

 nature and extent of induced movements, especially the differential movements 

 of gases, oils, and waters upon which recovery, together with the effects of 

 water upon recovery, very largely depend. It is further recognized that gas 

 mixed with oil facilitates lateral as well as vertical migrations of oil in water- 

 bearing strata. Again, it is recognized that there may be a limit to the fine- 

 ness of water-filled interstices beyond which viscous oils do not appear to 

 migrate 'gravitationally' under ordinary conditions. It is further recognized 

 that in a medium-grained, water-saturated sand a single globule of oil fails to 

 migrate 'gravitationally,' but as more globules of oil are added to it. there is 

 formed an aggregation of globules whose cumulative buoyancy is sufficient to 

 overcome the resistance to upward migration. Such relationships are im- 

 portant in the consideration of up-dip migrations. We must keep constantly 

 in mind the critical conditions up to which certain phenomena hold true, but 

 beyond which there are absolutely different phenomena. 



"Tlie field and laboratory investigations that the writer has so far made 

 indicate that under ordinary field conditions the up-dip migration of oil and 



