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Geochemical characterization and origin of Carabobo’s area formation water, Orinoco Oil Belt, Venezuela

Congress: 2008
Author(s): Moises Pirela, José Antonio García, José Rondón

Keyword(s): Orinoco Oil Belt, Carabobo area, formation water
Article: Poster:
AbstractIn 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.
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