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Recent publications

Workreport 2018-7



Matrix Porewater and Gases in Porewater in Olkiluoto Bedrock from Drilling OL-KR56


Eichinger, F., Rufer, D., Waber, H.N.



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Porewater from naturally saturated core samples taken between 700 and 1160 m b.s. from drillhole OL-KR56 were successfully characterised. Additionally to the porewater tracers Cl, Br, d37Cl, d18O and d2H, which were determined by indirect methods, reactive and noble gases in porewater were quantified and isotopically characterised. The data are interpreted in terms of the palaeohydrogeological history of the Olkiluoto investigation site. Therefore the new data sets are compared to porewater data from previous drillholes and to fracture groundwaters taken from previous drillholes and from drillhole OL-KR56.

Porewater Cl- and Br-concentrations show a significant increase between 750 and 770 m b.s. and subsequently vary slightly, except around water-conducting fractures, where lower porewater Cl- and Br-concentrations could be determined compared to samples more distant to those. Porewaters Cl- and Br-concentrations are lower than those of fracture groundwaters taken in drillhole OL-KR56 and previous drillholes, suggesting a transient state between both reservoirs. An exception from this trend could be observed in a depth of 770 m b.s., where porewater and fracture groundwater Cl- and Br-concentrations are similar. 

Porewater plot above the seawater dilution line on the Br vs Cl diagram suggesting a non-marine origin for dissolved Cl and Br.

Porewater d18O and d2H values become enriched mainly in 18O with depth and are generally more enriched in the heavy isotopes than porewaters from above and fracture groundwater from drillhole OL-KR56 and previous drillholes at similar depth.  They plot close or slightly to the right of the GMWL above those of porewater from shallower bedrock zones suggesting the presence of a meteoric water component formed under moderate to warm climatic conditions.


Volumes of reactive and noble gases in porewater vary with depth and with distance to the next water-conducting fractures. Porewater He volumes are generally higher than those dissolved in fracture groundwater, wheras porewater CH4 volumes are lower than those of fracture groundwaters from similar depth. Exceptions from this trend can be observed for porewater from samples taken at 747 and 1153 m b.s., which have CH4 volumes in the same range than fracture groundwaters taken at similar depths from previous drillholes.

Stable isotope signatures of hydrocarbons and hydrocarbon volume ratios indicate a thermogenic origin of the detected hydrocarbons, which probably originate from an external source.

Porewater 3He/4He ratios indicate a predominant crustal origin. The comparison with 3He/4He ratios in Olkiluoto bedrocks suggests an additional source besides the radiogenic crustal produced helium.


Porewater, stable isotopes, noble gases, reactive gases, porewater‒groundwater interaction, palaeo-hydrogeological evolution


WR 2018-07_web (pdf) (39.5 MB)


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