Hydrochemichal analysis thermal water Gross Schoenebeck, Germany

The main objective of the work package 2 of the REFLECT project is to characterise relevant fluid properties and their reactions for saline fluids (type C). One of the specific goals was to collect fluid samples from several saline fluids from geothermal sites across Europe, determine their properties, and thus contribute to the Fluid Atlas (WP3). Additionally, the REFLECT team will compare those field data with data from lab experiments performed at near natural conditions.

Samples of type C fluids were taken from several sites in Germany, Austria, Belgium and the Netherlands. The samples were analysed for major and minor ions, dissolved gases and isotopes.

In order to gain information about the increased methane content (about 65 vol-%) in the gas samples of the Groß Schönebeck production well (GrSk05/05) collected in February 2021 as compared to previous samples in 2010-2018 (10-14 vol-%), three gas samples were sampled by GFZ on 02 March 2021 at the valve at the wellhead when releasing the pressure from the wellhead. Main gas composition was measured by GFZ indicating again predominantly CH4 (63,9-64,2 Vol-%) followed by N2 (30,9 – 31,2 vol.-%) with minor amounts of H2 (3,4 vol-%) and CO2 (0,01-0,04 vol-%). Potential reasons for the increased methane content could be either microbial activity or contribution of fluid / gas from a different source within the reservoir. To determine the origin of methane, therefore, isotope analyses were performed. The samples arrived at Hydroisotop on March 13th 2021 for the analysis of higher hydrocarbons (C2-C5) and their isotopic composition (13C-CO2, 13C -CH4, 13C-CxHy and 2H-CH4). Together with the measured high amounts of higher hydrocarbons (ethane, propane etc.) they indicate a rather thermogenic source of the hydrocarbons. To better clarify the question of the source of methane, additionally, two downhole water samples from two different depths (1500 and 4000 m) were taken by GFZ on 09th and 10th of June 2021 and sent to Hydroisotop for analysis of main cations and anions, heavy metals, trace elements and isotopes (13C-CH4) in July 2021. The water sample composition resembles those of earlier measurements of samples collected in Groß Schönebeck (e.g. Regenspurg et al., 2010). However, since the well had not been in operation for a while a depth differentiation between the sample from 4000 m and the one from 1500 m is obvious. This was already visible by the black precipitate observed in the 4000 m sample, whereas the sample at 1500 m showed da reddish precipitate of presumably iron oxides. It should be noted that the nitrate content of the water samples is unusually high since reducing conditions are expected. This could have been caused by air contact of the sample and subsequent oxidation. Furthermore, a reduced silicon content shows in sample 365871 compared to sample 365870. Given the high temperature of the well, the higher silicon content is more plausible.

The dataset contains analysis results associated with the research project REFLECT. It is a comma separated file (csv) containing the following columns: Location,Country,Description,Laboratory (Lab.),Lab. No.,Sampling date,Sodium (mg/l),Potassium (mg/l),Calcium (mg/l),Magnesium (mg/l),Chloride (mg/l),Sulphate (mg/l),Nitrate (mg/l),Antimony (mg/l),Barium (mg/l),Bromide (mg/l),Fluoride (mg/l),Iodide (mg/l),Lithium (mg/l),Silicon (mg/l),Strontium (mg/l),Aluminium (mg/l),Arsenic (mg/l),Lead (mg/l),Copper (mg/l),Manganese total (mg/l),Nickel (mg/l),Uranium (mg/l),Zinc (mg/l),Ethane (vpm),Propane (vpm),i-Butane (vpm),n-Butane (vpm),i-Pentane (vpm),n-Pentane (vpm),Ethene (vpm),Propene (vpm),1-Butene (vpm),Carbon-13 d13C-CO2 (per mille VPDB),Carbon-13 d13C-CH4 (per mille VPDB),Deuterium d2H-CH4 (per mille VPDB),Carbon-13 d13C-C2H6 (per mille VPDB),Carbon-13 d13C-C3H8 (per mille VPDB),Carbon-13 d13C-i-C4H10 (per mille VPDB),Carbon-13 d13C-n-C4H10 (per mille VPDB)

Methods are described in the accompanying deliverable Fluid data of geothermal sites (type C).