Geoquímica do Petróleo – Oil Geochemistry
1rst Evaluation Test, 28-04-2015, IST
Question 1
Understanding the generative system is central to assessing the petroleum system(s). The search of
generative of oil, gas or condensate discovered is therefore at the heart of the geochemistry project. The
figure bellow presents a typical depth plot for TOC/Rock Eval and maturity data, also often called
geochemical log, from South Griffin J-13.
Figure 1
Taking into account the data of geochemical logging (Figure 1), comment the possibility of existing
contamination of results by drilling muds which have in their composition organic compounds (lignite,
lignosulfonate). Justify the answer based on table data.
Question 2
Portugal has very rich source rock from Jurassic epochs, as the case of Peniche basin (part of Lusitanian basin), as
is the case of Mcnb formation (20 m thick, average TOC value 3,8 - up to 14%, %).
Figure 2/Table 1 - Diagram of Hidrogen Index vs. Oxigen Index for samples of Peniche Basin - Portugal
(Pliensbachian Basin 189,6(?) Ma – 183,0 Ma)
CC – Cabo Carvoeiro, Mcnb – bituminous marls and limestones, Mcg – lumpy marls and limestones
a) Taking into account the data from the Van Krevelen modified diagram identify a source rock from Peniche Basin
that can have a major biological marine origin and another of terrestrial origin. Justify.
b) The Mcnb Formation (open squares) presents a very broad spectrum of data in the Van Krevelen diagram. Indicate
possible reasons that can explain that fact by using the data from the table 2.
Table 2- Mncb Formation – TOC /Rock Eval results
Depth TOC
HI
OI
S1
S2
S3 TMax