﻿PHTROLEUM 
  GEOLOGY 
  — 
  HEROY 
  173 
  

  

  Up 
  to 
  quite 
  recently 
  such 
  evidence 
  as 
  was 
  available 
  to 
  geologists 
  

   tended 
  to 
  show 
  that 
  petroleum 
  was 
  formed 
  at 
  the 
  time 
  of 
  deposition 
  

   and 
  buried 
  with 
  the 
  sediments 
  (McCoy, 
  1926, 
  p. 
  1022). 
  However, 
  

   extensive 
  chemical 
  examination 
  of 
  recent 
  marine 
  sediments 
  indi- 
  

   cates 
  that 
  petroleum 
  is 
  not 
  present 
  in 
  them 
  and 
  consequently 
  is 
  not 
  

   formed 
  at 
  the 
  time 
  of 
  deposition 
  or 
  shortly 
  thereafter 
  (Trask 
  and 
  

   Wu, 
  1930). 
  Recent 
  sediments, 
  therefore, 
  appear 
  to 
  have 
  reached 
  

   a 
  stage 
  in 
  their 
  history 
  at 
  which 
  the 
  bacterial 
  action 
  has 
  largely 
  run 
  

   its 
  course 
  but 
  at 
  which 
  petroleum 
  has 
  not 
  yet 
  been 
  formed. 
  The 
  

   organic 
  matter, 
  the 
  "mother 
  substance" 
  of 
  petroleum, 
  as 
  it 
  is 
  some- 
  

   times 
  called, 
  presumably 
  is 
  present 
  in 
  such 
  sediments 
  in 
  solid 
  form, 
  

   analogous 
  to 
  the 
  solid 
  bituminous 
  material, 
  called 
  "kerogen," 
  found 
  

   in 
  oil 
  shales 
  (McCoy 
  and 
  Keyte, 
  1934, 
  p. 
  271). 
  Berl 
  (1938, 
  p. 
  2) 
  

   considers 
  that, 
  after 
  bacterial 
  action 
  has 
  ceased, 
  carbohydrates, 
  

   humic 
  acids, 
  and 
  lignin 
  are 
  converted 
  into 
  intermediate 
  substances 
  

   which 
  he 
  calls 
  "protoproducts" 
  and 
  which 
  he 
  considers 
  the 
  parent 
  ma- 
  

   terials 
  for 
  petroleum. 
  Other 
  chemists, 
  notably 
  Hackford 
  (1932), 
  

   have 
  also 
  sought 
  to 
  trace 
  the 
  transformation 
  of 
  vegetable 
  matter 
  into 
  

   petroleum. 
  Most 
  chemists 
  consider 
  that 
  only 
  moderate 
  temperatures, 
  

   such 
  as 
  are 
  within 
  the 
  bounds 
  of 
  geologic 
  probability, 
  are 
  required 
  to 
  

   effect 
  such 
  changes. 
  Time, 
  of 
  which 
  the 
  geologist 
  sees 
  an 
  abundant 
  

   supply, 
  is 
  also 
  thought 
  to 
  be 
  an 
  important 
  factor 
  in 
  the 
  conversion. 
  

  

  Much 
  work 
  remains 
  to 
  be 
  done 
  before 
  the 
  various 
  steps 
  in 
  the 
  

   conversion 
  of 
  organic 
  matter 
  into 
  petroleum 
  can 
  be 
  accurately 
  traced. 
  

   At 
  some 
  stage 
  in 
  the 
  process 
  the 
  solid 
  organic 
  matter 
  laid 
  down 
  with 
  

   the 
  sediments 
  is 
  converted 
  into 
  fluids, 
  and 
  it 
  is 
  only 
  then 
  that 
  move- 
  

   ment 
  from 
  source 
  bed 
  to 
  reservoir 
  becomes 
  possible. 
  

  

  As 
  a 
  result 
  of 
  studies 
  of 
  crude 
  oils 
  in 
  the 
  Gulf 
  Coast, 
  Barton 
  (1934) 
  

   concluded 
  that 
  petroleum, 
  when 
  first 
  formed, 
  is 
  heavy 
  and 
  viscous 
  and 
  

   has, 
  as 
  the 
  result 
  of 
  the 
  operation 
  of 
  heat, 
  pressure, 
  and 
  perhaps 
  other 
  

   forces, 
  evolved 
  into 
  progressively 
  lighter 
  oils. 
  He 
  has, 
  however, 
  also 
  

   observed 
  that 
  deeper 
  oils 
  have 
  lower 
  specific 
  gravity 
  than 
  those 
  nearer 
  

   the 
  surface. 
  To 
  what 
  extent 
  this 
  relationship 
  may 
  be 
  explained 
  by 
  

   loss 
  of 
  volatile 
  constituents 
  through 
  escape 
  to 
  the 
  surface 
  is 
  unknown, 
  

   but 
  the 
  inference 
  of 
  recent 
  intensive 
  geochemical 
  studies 
  is 
  that 
  there 
  

   is 
  a 
  definite 
  upward 
  movement 
  of 
  hydrocarbons 
  from 
  the 
  reservoirs 
  

   to 
  the 
  surface, 
  even 
  though 
  the 
  cover 
  rocks 
  may 
  appear 
  highly 
  im- 
  

   pervious 
  to 
  such 
  migration. 
  

  

  GEOLOGIC 
  FORCES 
  OPERATING 
  TO 
  PRODUCE 
  PETROLEUM 
  

  

  The 
  chemical 
  reactions 
  required 
  to 
  produce 
  petroleum 
  from 
  the 
  

   "mother 
  substance" 
  have 
  presumably 
  not 
  occurred 
  spontaneously 
  but 
  

   have 
  been 
  brought 
  about 
  by 
  competent 
  physical 
  forces, 
  such 
  as 
  heat, 
  

   pressure, 
  and 
  movement. 
  All 
  these 
  forces 
  are 
  operative 
  in 
  deeply 
  

  

  