Page 158 - Geochemical Remote Sensing of The Sub-Surface

Light hydrocarbons for petroleum and gas prospecting 13 5

Sapropellc Humic
Source Source
.
.
.
.
20- ~/..... #41 - 68
Diagenesls
50 - -- 122
100 - - 212
Catagenesis

150-- - 302

200 - 392
Metamorphism Or
Relative Yield of Gas from
Organic Matter in Fine-Grained Sediments
Fig. 5-1. Generation of gases with depth: C2+ represents hydrocarbons heavier than CH4; N2 is
generated initially as NH3.

C2+[%1--~
I
10 20 30 50
Ro (%) I----hydrocarbons generated ---~l I I I I I l',*r-Q
]
/
-70 ~-70

- Imr,,.)~ "60
ol.5 ~-60 --e--~iZI I,

1.2 -40 -40 ~ . 9
2.0 t:~,/f/,,
3.0 xe
20
3~0 -20 I 9 , ?,V-r
100 90 80 70 50
Fig. 5-2. Genetic characterisation of natural gases by compositional and isotopic variation: (a)
formation of natural gas and petroleum in relation to maturity of organic matter; (b) relative
concentration of C2+ hydrocarbons in relation to ~3C in CH4, with arrows indicating compositional
changes due to shallow migration (Ms) and deep migration (Md) (reproduced with permission of
the American Association of Petroleum Geologists, whose permission is required for future use,
from Schoell, 1983, AAPG Bull., vol. 67, no. 12, Fig. l, pp. 2226-2227, AAPG 9