IWRA World Water Congress 2008 Montpellier France
4. Development of Water Resources and Infrastructure
Author(s): Moises Pirela
José Antonio García
José Rondón
Keyword(s): Orinoco Oil Belt, Carabobo area, formation water
Article: PDFPoster: PDFAbstractIn the oil industry, the formation water requires a detailed geochemical and
hydrologic characterization (Archer and Wall, 1994) since the establishment of type and origin of this bodies water
allow it to deduce the vertical and horizontal proximity of a certain hydrocarbons reservoir, as well as providing
esentail parameters such as salinity to calculate the oil reserves. In that sense, the main objective of the present study
was to characterize and to establish the origin of the formation water in the Carabobo’s area (formerly Cerro Negro)
located in the Orinoco Oil Belt (FPO) through classical system (Stiff, Sulin y Piper) looking for its integration with the
others fluids present in the reservoir.
32 samples of water formation of different depth were used for this study.
These samples were extracted during the perforation of 11 stratigraphic wells. It was determinated dissolved species
concentration (Na+, K+, Ca2+, Mg2+, Cl-, SO42-), alkalinity (HCO3- y CO32-), pH, conductivity and
temperature. The water samples for the analysis of dissolved species were stored in HDPE bottles, prefiltered with
0.45 μm filters, acidified with HNO3. Dissolved species determination followed established procedure in
ISO-11885 and ASTM D-4327 metodologic norm.
The analysis of Piper’s diagram allow to identify three types
of formation water: Na-HCO3, Ca-HCO3 (C well) y Na-Cl-HCO3 (D well). It can be seen that most of samples
present excess of Na+ (not compensated by Cl-) indicate an additional source besides halite dissolution (Kharaka
and Hanor, 2003). The Na+ excess can be compared with HCO3- it show good correlation with line that possibly
indicate excess of Na+ was generated by dissolution of sodium-rich mineral such as albite (NaAlSi3O8) (Cheng et
al., 2006):
2NaAlSi3O8 (s)+ 2H2CO3 (aq)+ 4H2O(l) 2Na+(aq) + 2HCO3-(aq)+ 4H4SiO4(aq) +
Al2Si2O5(OH)4(s)
Those samples, that deflect of this tendency, indicate another process must add Na+. On the
other hand, Stiff´s figures suggest an meteoric origin that match with other results. The C (shallower sample) and D
wells Stiff’s figure show the existence of connate water although Na/Cl relation suggest a meteoric origin for C well
sample and connate for D well sample. This indicate the presence of a mixture zone between connate water (Na-Cl)
and meteoric water (Na-HCO3) at southwest to area or communication of sands in the reservoir. Due to this fact, it
can be conclude that in the research area, exist predominance of formation water type Na-HCO3 with meteoric
origin and that the application of standard systems it allowed the characterization and the birth determination of the
formation water in the Carabobo’s area from Orinoco Oil Belt, in addition of determination a mixture zone at area‘s
southwest.