Page 103 - The Petroleum System From Source to Trap

5. Applied Source Rock Geochemistry 97

Maceral
•• �.:tryococcus Groups
o.� %R0

\ Resinite
- -
..,. .- - - - .... . . Tasmanites w
,. ... ·. . ....
z
- - - - - - ':" i=
Cl..
- - - ::::;
I I . Sporinite %TYPE X H / C = � H / C
---
�
�
�
�
-- --
--
1.3 � � � � � � � � -- � � � - - - - - .:., Cutinite � -- -- �--- 0.20 X 1 . 3 = 0.26
\ Desmocollinite
w
....
z
ii
....
>
0.60 X 0.85 = 0.51
! Semi-fusinite

0.20 X 0.50 = 0.10
ESTIMATED H / C � 0.90

lsorank

�:2 Zone of Oil Generation

o �-----------------------------------------
0 0.05 0.1 0.15 0.20
Atomic 0 / C
Figure 5.2. Combined use of organic petrography, elemntal analysis, and Rock-Eval pyrolysis and TOC improves confi­
dence in assessment of the quality and maturity of kerog in rock samples. A sample analyzed by Rock-Eval pyrolysis was
charactzed as being marginally mature (T max = 435•c) and gas prone (HI = 150 mg HC/g TOC). Organic petrography shows
a T AI of 2.5, an R0 of 0.5% (supporting the maturity assessment from pyrolysis), and the following maceral composition:
type II 20%, type Ill 60o/ o , and type IV 20%. The calculated atomic KIC (0.90) corresponds with that determined by elemental
analysis, supportng a dominanUy gas-prone character. (Concept for figure courtesy of T. A. Edison.)

carbon. During catagenesis and metagenesis, all is the structureless constituent of vitrinite, whereas
kerogens approach graphite in composition (nearly pure telinite is the remains of cell walls of land plants. Figure
carbon) near the lower left portion of both diagrams 5.2 shows two types of collinite: telocollinite contains no
(Figure 5.1). inclusions and is the maceral recommended for vitrinite
reflectance measurements, whereas desmocollinite shows
Maceral Groups submicroscopic inclusions of liptinite and other
materials. Because of the inclusions, desmocollinite
The three principal maceral groups in coal and sedi­
shows a higher atomic H/C, has a lower reflectance
mentary rocks are liptinite (exinite), vitrinite, and inertinite (Figure 5.3), and commonly fluoresces under ultraviolet
(Stach et al., 1982). Liptinite macerals, such as alginite, light, unlike telocollinite. Inertinitic macerals, such as
sporinite, cutinite, and resinite, generally mature along semi-fusinite and fusinite, mature along the type IV
the type I or II kerogen pathways on the van Krevelen kerogen pathway. Because of the combined effects of
diagram (Figure 5.2). Preserved remains of the algae diagenesis, thermal maturity, and differing organic
Botryococcus and T a smanites are examples of structured matter input, a kerogen can plot anywhere on the van
alginite. Vitrinite macerals originate from land plants Krevelen diagram and need not fall on any of the
and mature along the type IIl kerogen pathway. Collinite indicated maturation curves.