﻿PETROLEUM 
  GEOLOGY 
  — 
  HEROY 
  179 
  

  

  This 
  concept 
  has 
  been 
  developed 
  by 
  Illing 
  (1933) 
  who 
  called 
  the 
  

   process 
  "filtration." 
  It 
  was 
  also 
  well 
  described 
  by 
  Versluys 
  (1932) 
  

   who 
  remarked 
  that 
  "fine 
  grained 
  strata 
  act 
  as 
  screens 
  when 
  water, 
  

   charged 
  with 
  small 
  globules 
  of 
  oil 
  or 
  minute 
  bubbles 
  of 
  gas, 
  is 
  forced 
  

   through 
  them." 
  

  

  By 
  some 
  such 
  mechanism 
  petroleum 
  has 
  moved 
  from 
  the 
  source 
  beds 
  

   into 
  the 
  more 
  porous 
  beds 
  throughout 
  the 
  entire 
  extent 
  of 
  their 
  con- 
  

   tact. 
  Information 
  gained 
  over 
  many 
  years 
  by 
  drilling 
  into 
  porous 
  

   beds 
  has 
  shown 
  that 
  it 
  is 
  exceptional 
  that 
  more 
  than 
  a 
  small 
  part 
  of 
  the 
  

   entire 
  area 
  of 
  a 
  porous 
  bed 
  is 
  saturated 
  with 
  oil 
  and 
  gas; 
  by 
  far 
  the 
  

   larger 
  part 
  contains 
  water. 
  It 
  seems 
  evident 
  that 
  in 
  some 
  manner 
  

   the 
  petroleum 
  must 
  have 
  been 
  collected 
  from 
  the 
  wide 
  areas 
  through- 
  

   out 
  which 
  it 
  entered 
  the 
  porous 
  beds 
  and 
  concentrated 
  in 
  the 
  relatively 
  

   much 
  smaller 
  areas 
  which 
  it 
  is 
  now 
  found 
  to 
  occupy. 
  2 
  The 
  movement 
  

   by 
  which 
  this 
  has 
  been 
  accomplished 
  is 
  essentially 
  a 
  lateral 
  movement, 
  

   one 
  which 
  continues 
  until 
  the 
  petroleum 
  reaches 
  a 
  stratigraphic 
  or 
  

   structural 
  trap. 
  

  

  An 
  explanation 
  of 
  this 
  movement 
  which 
  is 
  satisfactory 
  to 
  the 
  

   geologist 
  and 
  which 
  will 
  withstand 
  successfully 
  the 
  criticism 
  of 
  the 
  

   physicist 
  has 
  been 
  difficult 
  to 
  attain. 
  The 
  earlier 
  geologists 
  had 
  a 
  

   simple 
  and, 
  to 
  them, 
  complete 
  explanation. 
  Oil 
  and 
  gas, 
  being 
  lighter 
  

   than 
  water, 
  floated 
  above 
  it 
  and 
  filled 
  the 
  highest 
  portion 
  of 
  the 
  porous 
  

   rock. 
  Abundant 
  evidence 
  accumulated 
  which 
  was 
  considered 
  to 
  sup- 
  

   port 
  the 
  principle 
  of 
  flotation, 
  and 
  it 
  became 
  quite 
  generally 
  accepted, 
  

   along 
  with 
  the 
  corollary 
  that, 
  if 
  the 
  dip 
  of 
  the 
  porous 
  beds 
  were 
  suffi- 
  

   cient 
  to 
  overcome 
  friction, 
  the 
  particles 
  of 
  oil 
  and 
  gas 
  would 
  gradually 
  

   move 
  up 
  the 
  slope 
  to 
  the 
  pool, 
  the 
  gas 
  with 
  its 
  lower 
  specific 
  gravity 
  

   occupying 
  the 
  higher 
  places 
  (Griswold 
  and 
  Munn, 
  1907, 
  p. 
  24). 
  

  

  Munn 
  (1909) 
  was, 
  perhaps, 
  the 
  first 
  to 
  question 
  the 
  adequacy 
  of 
  

   flotation 
  or 
  buoyancy 
  to 
  account 
  for 
  the 
  accumulation 
  of 
  oil 
  pools, 
  

   considering 
  that 
  the 
  enormous 
  pressures 
  developed 
  in 
  oil 
  and 
  gas 
  wells 
  

   were 
  not 
  satisfactorily 
  explained 
  by 
  it. 
  Following 
  him, 
  other 
  in- 
  

   vestigators 
  down 
  to 
  the 
  present 
  have 
  thought 
  that 
  flotation 
  alone 
  

   could 
  not 
  produce 
  migration. 
  Illing 
  (1938b) 
  says 
  : 
  

  

  It 
  is 
  therefore 
  not 
  at 
  all 
  certain 
  from 
  first 
  principles 
  that 
  gas, 
  oil, 
  and 
  water 
  will 
  

   separate 
  out 
  by 
  flotation 
  in 
  the 
  pores 
  of 
  the 
  rock, 
  and 
  it 
  is 
  clear 
  that 
  the 
  separation 
  

   will 
  depend 
  upon 
  certain 
  limiting 
  conditions, 
  the 
  relative 
  importance 
  of 
  surface 
  

   tension 
  and 
  buoyancy. 
  

  

  1 
  Some 
  geologists, 
  on 
  the 
  contrary, 
  consider 
  that 
  the 
  accumulation 
  of 
  oil 
  takes 
  place 
  essen- 
  

   tially 
  in 
  situ 
  (McCoy 
  and 
  Keyte, 
  1934) 
  and 
  is 
  due 
  to 
  the 
  juxtaposition 
  of 
  rich 
  source 
  bed 
  

   and 
  reservoir. 
  Clark 
  (1934) 
  also 
  favors 
  this 
  view, 
  explaining 
  the 
  absence 
  of 
  oil 
  in 
  some 
  

   apparently 
  favorable 
  traps 
  by 
  the 
  absence 
  of 
  rich 
  source 
  beds 
  In 
  their 
  immediate 
  vicinity. 
  

   It 
  would 
  appear 
  to 
  the 
  writer 
  coincidental 
  that 
  zones 
  of 
  unusually 
  rich 
  source 
  material 
  

   should 
  have 
  been 
  formed 
  in 
  the 
  source 
  rocks 
  in 
  the 
  same 
  localities 
  that 
  later 
  become 
  the 
  

   loci 
  where 
  traps 
  were 
  formed 
  by 
  structural 
  deformation. 
  The 
  writer 
  thinks 
  that 
  the 
  organic 
  

   matter 
  has 
  been 
  more 
  uniformly 
  distributed 
  and 
  that 
  wider 
  areas 
  have 
  been 
  drawn 
  upon 
  to 
  

   fill 
  the 
  traps. 
  

  

  