﻿PETROLEUM 
  GEOLOGY 
  — 
  HEROY 
  177 
  

  

  MIGRATION 
  FROM 
  SOURCE 
  BED 
  TO 
  CARRIER 
  BED 
  

  

  The 
  compaction 
  of 
  sediments 
  by 
  the 
  increasing 
  load 
  of 
  younger 
  beds 
  

   deposited 
  in 
  succession 
  is 
  accompanied 
  by 
  the 
  loss 
  of 
  a 
  large 
  part 
  of 
  the 
  

   interstitial 
  water 
  they 
  originally 
  contained 
  (Athy, 
  1930). 
  The 
  con- 
  

   nate 
  water 
  remaining 
  in 
  the 
  sediments 
  adheres 
  closely 
  to 
  the 
  individual 
  

   grains 
  and 
  fills 
  the 
  intervening 
  voids. 
  Because 
  of 
  the 
  presence 
  of 
  this 
  

   film 
  of 
  closely 
  adhering 
  water, 
  which 
  is 
  present 
  even 
  in 
  well-saturated 
  

   oil 
  reservoirs, 
  it 
  is 
  probable 
  that 
  petroleum 
  normally 
  does 
  not 
  wet 
  the 
  

   grains 
  but 
  remains 
  in 
  the 
  interstitial 
  passages 
  in 
  the 
  form 
  of 
  minute 
  

   globules 
  (Schilthuis, 
  1937, 
  p. 
  200). 
  The 
  movement 
  of 
  the 
  interstitial 
  

   water 
  is 
  regarded 
  as 
  the 
  principal 
  cause 
  of 
  the 
  migration 
  of 
  oil 
  from 
  

   the 
  source 
  beds. 
  The 
  outward 
  movement 
  of 
  water 
  from 
  such 
  sedi- 
  

   ments 
  will 
  be 
  in 
  the 
  direction 
  of 
  least 
  resistance, 
  from 
  the 
  clays 
  and 
  

   marls 
  into 
  the 
  more 
  permeable 
  strata. 
  If 
  at 
  the 
  time 
  this 
  outward 
  

   movement 
  is 
  in 
  progress 
  petroleum 
  has 
  already 
  formed 
  in 
  the 
  sedi- 
  

   ments, 
  it 
  may 
  be 
  expected 
  to 
  move 
  with 
  the 
  expressed 
  water 
  into 
  the 
  

   more 
  porous 
  beds 
  which 
  are 
  competent 
  to 
  act 
  as 
  carriers 
  (Illing, 
  1933). 
  

  

  With 
  the 
  passage 
  of 
  time 
  and 
  the 
  completion 
  of 
  the 
  cycle 
  of 
  deposi- 
  

   tion 
  the 
  sediments 
  gradually 
  become 
  lithified 
  and 
  a 
  condition 
  will 
  ulti- 
  

   mately 
  be 
  reached 
  in 
  which 
  the 
  compaction 
  of 
  the 
  deeper 
  beds 
  will 
  cease. 
  

   The 
  more 
  competent 
  members 
  of 
  the 
  series 
  will 
  acquire 
  strength 
  to 
  sus- 
  

   tain 
  the 
  load 
  of 
  the 
  overlying 
  sediments, 
  and 
  the 
  fluids 
  which 
  they 
  

   contain 
  will 
  reach 
  a 
  state 
  of 
  equilibrium. 
  

  

  Capillarity 
  has 
  also 
  been 
  thought 
  competent 
  to 
  cause 
  the 
  movement 
  

   of 
  petroleum 
  from 
  the 
  source 
  bed 
  to 
  the 
  carrier 
  bed. 
  McCoy 
  (1926, 
  p. 
  

   1027) 
  concluded, 
  on 
  the 
  basis 
  of 
  experimental 
  evidence, 
  that 
  there 
  is 
  

   an 
  interchange 
  of 
  fluids 
  between 
  the 
  source 
  bed 
  and 
  the 
  carrier 
  bed, 
  

   the 
  oil 
  in 
  the 
  source 
  bed 
  being 
  expelled 
  into 
  the 
  more 
  porous 
  bed 
  and 
  

   replaced 
  by 
  an 
  equal 
  amount 
  of 
  water. 
  This 
  interchange 
  was 
  thought 
  

   to 
  occur 
  in 
  the 
  capillary 
  spaces 
  of 
  the 
  source 
  rock 
  and 
  to 
  be 
  caused 
  

   by 
  the 
  superior 
  surface 
  tension 
  of 
  the 
  water 
  ; 
  the 
  water, 
  having 
  a 
  greater 
  

   adhesive 
  tension 
  for 
  the 
  wall 
  of 
  the 
  capillary 
  than 
  does 
  the 
  oil, 
  and 
  

   its 
  adhesive 
  tension 
  for 
  the 
  wall 
  of 
  the 
  capillary 
  being 
  greater 
  than 
  the 
  

   surface 
  tension 
  of 
  the 
  oil, 
  the 
  oil 
  column 
  in 
  the 
  capillary 
  would 
  be 
  

   broken, 
  and 
  minute 
  globules 
  of 
  oil 
  would 
  be 
  split 
  off 
  and 
  moved 
  through 
  

   the 
  capillary 
  in 
  the 
  direction 
  of 
  the 
  more 
  permeable 
  bed. 
  

  

  Other 
  forces 
  which 
  have 
  been 
  considered 
  as 
  contributing 
  to 
  the 
  move- 
  

   ment 
  of 
  oil 
  from 
  denser 
  to 
  more 
  porous 
  rocks 
  are 
  artesian 
  circulation 
  

   and 
  diastrophic 
  movements 
  in 
  the 
  sedimentary 
  basin. 
  The 
  effective- 
  

   ness 
  of 
  the 
  first-mentioned 
  is 
  questionable, 
  for 
  artesian 
  flow 
  is 
  likely 
  

   to 
  take 
  place 
  through 
  the 
  most 
  porous 
  beds 
  and 
  is 
  unlikely 
  to 
  be 
  effec- 
  

   tive 
  in 
  the 
  denser 
  sediments. 
  Diastrophism 
  may 
  have 
  been 
  effective 
  

   in 
  creating 
  compressive 
  forces 
  which 
  may, 
  in 
  turn, 
  have 
  acted 
  on 
  the 
  

  

  