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The natural history of petroleum

a schematic cartoon

Railsback's Petroleum Geoscience andSubsurface Geology faccbook.com/Amazing6cologist

Photosynthesis

Seeps

Erosional exhumation

Seeps

20°C Sea level

Sedimentary organie matter

Deposition Diagenetic \

......microbial

degradationflf \

..-^rrzrr^7Ke,^L_n

OilShale

Methane

Trapping

Gas chimney

Gas chimney

Late bacterial degradation

Heavy Oil / Tar

(e.g . Aihabasca or Orinoco)

40 C

Burial

^^Heąvy Ojl..

'"(eilher tor lac* of thermal crackng or bccauso ot :fObiai dogradationi^-^'^

Oil

window

Kerogen    ^x

\\

%■

Catagenesis

............... <9/0

Leakage of ~~ traps & sealś" ■"'"Non-Pasteurized reservoirs Pasteurized reservoirs^-^---

Late bacterial ,dęg_rądatip_n

Heavy Oil / Tar

.    60°C

Thermal limit of

petroleum-degrading rmerobes

(undegraded) Oil

Up-dip flushing of oil by gas

----Thermal breakdown

of oil to gas

y / Migration X Trapping Spili points / .

Trapping

100°C

120°C

140°C

160°C

Gas

window

Migration

180 C

Gas

200°C

220 C

Metagenesis

240’C

260 C

280 C

Substance

Transformative process Change ofposition in Earth

Oil Gas

Generation of hydrocarbons

This document attempts to synthesize some ideas about the origin and fate of mobile hydrocarbons in the subsurface. Its sources rangę in age at least from Gussow (1954. Buli. AAPG) to Head et al. (2003, Naturę) and beyond.

The many pathways of migration and leakage shown are best envisioned in three or morę dimensions, rather than in the two possible here. The closer spacing of isotherms at depth is only a means to conserve space and is not an indica-tion of inereasing geothermal gradient with depth.

LBR NaturaIHistoryofPetroleumCG odg 9/2011 revised 11/2011