HR: 0800h
AN: V31A-1421    [Abstracts]
TI: Chemical Characterization of Brines from Selected Oil Fields, Tabasco, M‚xico
AU: * M‚ndez-Ortiz, B
EM: bmendez@geociencias.unam.mx
AF: Centro de Geociencias-UNAM, AP 15, Juriquiila, Queretaro, QRO 76230 Mexico
AU: Carrillo-Chavez, A
EM: ambiente@geoiencias.unam.mx
AF: Centro de Geociencias-UNAM, AP 15, Juriquiila, Queretaro, QRO 76230 Mexico
AU: Tritlla, J
EM: jordit@geociencias.unam.mx
AF: Centro de Geociencias-UNAM, AP 15, Juriquiila, Queretaro, QRO 76230 Mexico
AU: Levresse, G
EM: glevresse@geociencias.unam.mx
AF: Centro de Geociencias-UNAM, AP 15, Juriquiila, Queretaro, QRO 76230 Mexico
AU: Gonzalez-Partida, E
EM: egp@geociencias.unam.mx
AF: Centro de Geociencias-UNAM, AP 15, Juriquiila, Queretaro, QRO 76230 Mexico
AU: Oviedo-Perez, A
EM: aoviedop@pep.pemex.com
AF: PEMEX-PEP, Activo Reforma-Comalcalco, Villahermosa, TAB 86038 Mexico
AU: Martinez-Kepm, H
EM: hmartinezk@pep.pemex.com
AF: PEMEX-PEP, Activo Reforma-Comalcalco, Villahermosa, TAB 86038 Mexico
AU: Gonzalez-Posadas, F
EM: fgonzalezpo@pep.pemex.com
AF: PEMEX-PEP, Activo Reforma-Comalcalco, Villahermosa, TAB 86038 Mexico
AU: Clara-Valdes, L
EM: lrclarav@pep.pemex.com
AF: PEMEX-PEP, Activo Reforma-Comalcalco, Villahermosa, TAB 86038 Mexico
AB: Thirteen brine samples were recovered from nine oil-producing wells in the Agave (Cretaceous) and Saramako (Cretaceous and Tertiary) oil fields. These samples were analyzed for major and trace elements as well as O and D isotopic compositions. The goal of this study was to compare the possible links between oil-related brines enclosed within Cretaceous and Tertiary productive horizons that were thought to have similar origin oils. The salinity of the Saramako Cretaceous and Tertiary horizons is very constant, around 30000 ppm, one to six times lower than the salinities found in the Agave Cretaceous Field (from 45000 to 170000 ppm). Major ion chemistry suggests that brines are in equilibrium with the host rock. One of the main difference, besides Mg, resides in the S concentrations, were Agave samples present lower concentrations, probably related to the presence of abundant sulfides in the aquifer's rock. Halogen (Br, Cl) systematics indicates a different origin for the Saramako and Agave brines. The Saramako samples halogen composition plot near normal seawater both in the Na/Cl vs Cl/Br (molar ratios) and the Cl vs Br (ppm) plots. The Agave halogen data scatter near and underneath the seawater evaporation line in the Na/Cl vs Cl/Br (molar ratios), suggesting that these fluids could represent seawater evolved past the point of halite precipitation. The Cl vs Br (ppm) plot indicates that these fluids undergone some degree of mixing with low-salinity fluids, probably seawater. The presence of two different groups of data suggests the compartment of the aquifer. The \deltaD and \delta18O data show strong differences between the Saramako and Agave brines. The Saramako brine \delta18O and \deltaD isotopic compositions are +2.1% (VSMOW) and -13.8% respectively. The Agave samples have a \delta18O composition from +4.3% to +6.0% and \deltaD isotopic composition from -20.0% to -12.6%. Differences in \delta18O compositions between Saramako and Agave brines indicate that the latter fluids were in equilibrium with the host dolostones at certain temperature. Saramako brine composition indicates a near-pristine seawater origin. Agave brines chemical composition suggests an origin related with a bittern formed after evaporation of seawater past the point of halite precipitation, subsequently mixed with seawater. Oxygen isotopic compositions reflect both different host rock and water to rock interaction phenomena, whereas hydrogen isotopic composition can be modified by diagenetic reactions.
DE: 4825 Geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting