25th International Meeting on Organic Geochemistry IMOG 2011

P-346
Diamondoids, a tool in the geochemical studies to identify
compartmentalized reservoirs
Adriana Pérez 1 , Ingrid Alfonzo 1 , Federico Galarraga 2 , Carmen Rodríguez 1 , Ricardo
Harner 1 , Ysmarline Rincones 1
1 PDVSA-Intevep, S.A., Los Teques, Venezuela (Bolivarian Republic of), 2 Instituto de Ciencias de la Tierra.
Universidad Central de Venezuela, Caracas, Venezuela (Bolivarian Republic of) (corresponding
author:perezacy@pdvsa.com)
In this study were evaluated the distribution
specifically diamondoids group of adamantanes and
diamantanes, in condensate samples from two
producing fields (Santa Rosa and Pirital) in the area
of the Oriental Basin of Venezuela, in order to assess
geochemical parameters proposed based on the
abundance, distribution and relations of diamondoids
compounds to identify families and/or groups that
permit the inference reservoir communication.
These compounds were analyzed by CG-MS and
quantified by using certified standards (adamantane;
1-methyladamantane; 1,3-dimethyladamantane;
1,3,5-trimethyladamantane; 2-methyladamantane;
1,4-dimethyladamantane (cis); -1,4dimethyladamantane
(trans); 1,2-
dimethyladamantane; 1-ethyladamantane; 1-ethyl-3methyladamantane;
2-ethyladamantane, diamantane
and 1-methyldiamantane). The following ions were
monitored for diamondoids analysis: m/z 135, 136,
149, 163, 187 and 188.
In the Santa Rosa Field were evaluated the CW-1,
CW-2, CW-3 and CW-4 samples, which are come
from Interval B of San Juan Formation of Cretaceous
age (Maastrichtiense), Interval A of Vidoño Formation
of Cretaceous (Campanian) - Tertiary (Early Eocene)
age, and the sands of Oficina Formation of Early-
Middle Miocene age, interval K and I of Moreno
Member, respectively. In the Pirital Field, the samples
evaluated: CY-1, CY-2, CY-3 and CY-4,
corresponding from 4 wells producing from some
sandstones Naricual Formation of Late Oligocene
Early Miocene age, only the sample CY-2 was taken
from the sand KP corresponding to Cretaceous-
Paleocene (?) unit. The concentration of diamondoids
compounds in samples condensates were in a range
from 121.82 to 22563.63 ppm (mg/L), considering all
the compounds evaluated in two fields.
In the Santa Rosa Field, according to the previous
characterization of the samples, the condensed CW-1
and CW-2 are compositionally correlated, thus
suggesting that units have vertical communication.
For samples CW-3 and CW-4, they also reveal
vertical communication because the samples are
compositionally similar, but different to samples CW-1
and CW-2. In both cases, the abundance of
diamondoids compounds in terms of concentration
were similar (relatively similar orders of magnitude) in
addition to the parameters of maturity, level of
biodegradation and depositional environments as well
as type of organic matter were similar for each of the
families or groups of samples. These results support
the compartmentalization of these reservoirs.
In the Pirital field, samples CY-1 and CY-3 showed a
positive correlation in the parameters evaluated from
the concentration of diamondoids compounds
confirming the communication of fluids. It was
suggested to by other author through the analysis
conventional parameters. The CY-2 and CY-4
samples even previous studies suggest that they are
compositionally similar however, from the point of
view of diamondoids concentration there is differ
considerably by several orders of magnitude, so these
samples are not similar, and this which might suggest
that both reservoir (Cretaceous - Paleocene unit (?))
and sand 5 of Naricual Formation) are not connected.
Regarding the parameters evaluated as source,
maturity and alteration by biodegradation, only there
are differences in the EAI (Index Ethyl-Adamantane)
which assesses the relationship origin. It could
explain the high concentration of diamondoids in the
sample CY-4. It is possible that condensates might be
related to variation in organic facies of the source rock
presenting a mayor terrestrial input, which could
explain the high values obtained in the EAI. However,
it requires further study in determining the
concentration of diamondoids in the condensates
produced in that field, so to determine if the
characteristics of this sample are identify in other
condensates.
477