Page 41 - The Petroleum System From Source to Trap

2. Petroleum System Logic as an Exploration Tool 33

HYDROGEN CUTTINGS
% R o TOC wt.% KEROGEN* I N DEX GAS
0 2 0 6 1 2 4 0 1 0 5 1 2 5 10 TYPE HC (mg) WETNESS
0 • 0 roc g
% %
• 8 0 � � • 0 o .---,.-.....::,s..o_-__.:o o 0 0 so 100
•
100 200 3oo o
., o
2 •., 0 at
't;
•
3 .. �( lBO
� • 0 �� 2 0 c 0 C>'
••
4 a• � 3 � 0 0
0
0
5 .x> • <0., •C< AI: 4 �,8o
o"j
�
•
w 1- 6 0 � 0
z u.. 5 §Eo 0
w 7 'i* oO 0
(J �
o'
0 J: �I .. 0 ?, 0
I
CJ
::::i � 8 .?. 'i 8 q, ,. -�
0
0 w ca. r\ �0
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c 9 aO I 0 0 eo
el J. •
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10 •
0.\'
0
1 oil 0 0 p� �- ""
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5
• CORE LAB. o GEOCHEM LAB., 14
DATA FROM OCS REPORT MMS 86003 *SHELL DEVELOPMENT
*·----* CALCULATED BY SHELL DEVELOPMENT 1 5 �------�
[Z] AM. CJ VITR. GEOCHEM LABORATORIES
- EX. - INERT. OCS REPORT MMS 86003
Figure 2.12. Vitrinite reflectance (R0) and total organic
carbon (TOC) for the COST-1 well in the St. Lawrence Figure 2.13. Kerogen type by visual analysis, hydrogen
subbasin. See Figure 2.11 for well location. index by Rock-Eval pyrolysis, and cuttings gas wetness for
the COST-1 well, St. Lawrence subbasin. See Figure 2.11
for well location. Abbreviations: AM, amorphous; EX,
have followed the nomenclahrre used by Worrall (1991). exinite; VITR, vitrinite; INERT, inertinite.
The basement underlying the Norton basin consists of
Precambrian-Paleozoic metamorphics intruded by
Cretaceous granites. Worrall (1991) showed that there are include nonmarine coastal, deltaic, shallow marine, and
two distinct sedimentary rock packages above the possibly lacustrine. This sedimentary rock package forms
basement. The boundary between these two packages is an onlap sequence on paleobasement highs and basin
an unconformity that Worrall calls the "red event." Here margins. Traps include sedimentary rock drape over
we refer to the older of these two sedimentary rock basement highs, faults, pinchouts, and onlaps.
packages as the "pre-red sequence." At the time of the
sale, the age of the red event was poorly established but Part 1: Evaluation of Oil Charge
was thought to be Paleocene. The age of the red event is
now thought to be late middle Eocene (44-43 Ma) Initial Interpretation
(Worrall, 1991). We refer to the younger of the two sedi­ Geochemical data for the COST-1 and COST-2 wells
mentary rock packages as the "basin fill sequence." are shown in Figures 2.12-2.15. Most of these data were
Infolded remnants of the pre-red sequence are locally published by Turner et al. in 1986. The interval shallower
present at various spots in the Norton basin and were than 7000 ft can be ignored in both wells because it does
found in both COST wells. Coals are present in the pre­ not attain the thermal maturity level required for signifi­
red sequence in both COST wells. An abrupt increase in cant oil expulsion. Visual kerogen analysis by Shell
vitrinite reflectance to about 1.0% Ro was observed at the Development for COST-1 (Figure 2.13) and by Robertson
red event in both COST wells. We assumed that any Research (U.S.) for COST-2 (Figure 2.15), with which
potential for significant oil generation in the pre-red Shell concurred, suggested a large fraction of oil-prone
section was destroyed at the COST well locations prior to (lipid) kerogen from about 9000 ft to the unconformity at
deposition of the basin fill sediments. about 12,000 ft in both wells. The vitrinite reflectance is
Slow subsidence with some associated faulting started lower in this mixed lipid and humic system than would
in late Eocene and has continued to the present day. be observed in a pure humic coal. To avoid this source of
Depositional environments in the basin fill sequence error, the calculated trend of vitrinite reflectance versus