--> ABSTRACT: Characterization of Fluids and Their Products in a Recent, Fault-Related Hydrothermal System, Case Study from the Buda Thermal Karst, Hungary, by Erőss, Anita; Madl-Szőnyi, Judit; Csoma, Anita; #90135 (2011)

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Characterization of Fluids and Their Products in a Recent, Fault-Related Hydrothermal System, Case Study from the Buda Thermal Karst, Hungary
Erőss

, Anita 1; Madl-Szőnyi1, Judit 1; Csoma, Anita .2
(1)Physical and Applied Geology, Eötvös Loránd University, Budapest, Hungary. (2) Subsurface Technology Basin and Sedimentary Systems, ConocoPhillips, Houston, TX.


Carbonate rocks are important reservoirs of water and hydrocarbon. The attention of the petroleum industry in the last years has turned to the research of fault-related hydrothermal karst reservoirs. These are hypogenic karsts according to the recent classification of such systems. The pitfalls, challenges and associated uncertainties of reservoir diagenetic studies is that the diagenetic fluids that were responsible for porosity enhancement or destruction in the reservoirs cannot be directly sampled. One way to overcome these challenges is to study analogue modern karst systems, where the fluids, their dynamics and effects can be investigated. The most appropriate place to sample these fluids and products is the regional discharge zone of a hypogenic karst.

The Buda Thermal Karst system (Budapest, Hungary) is one of the few sites, where fault-related hydrothermal and mixed hydrothermal-meteoric fluids can be studied in situ, and their effects on carbonates can be evaluated. As the result of the interaction of discharging waters and carbonates, extensive cave systems has developed and still developing today.

A comprehensive hydrogeological study was initiated and carried out for the characterization of processes and products at the discharge zone of the Buda Thermal Karst. Methods included hydrogeochemical, mineralogical and microbiological investigations.

Among the results of the study, it was found that the morphology of the caves rather controlled by the composition of fluids and their discharge distribution, than by the lithology of the host rock. In addition, several processes were identified which can be responsible for cave development and formation of minerals and which can act even simultaneously. Among them mixing corrosion and microbially mediated sulphuric acid speleogenesis have crucial role. However, based on the differences in fluids and their discharge distribution, different cave forming processes dominate in the studied areas.

During the analyses of cave minerals it was demonstrated that common occurrence of iron-hydroxide precipitates (characterized by high trace element content) with calcite rafts is conclusive for cave formation, thus this paragenesis can be used as cave level marker in palaeo systems.

The study is provided hydrogeological workflow and quantitative data set for fluid compositions and cave dimensions for a hypogenic karst system, which can be used as input data for modelling purposes.

 

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.