Hydrogen sulphide (H2S) occurs in groundwater in various lithostratigraphic units of the Zechstein Basin in the Legnica-Głogów Copper Basin (SW Poland). This region is located in the Fore-Sudetic Monocline within which, several tens of kilometres NE of the study area, at greater depths, natural gas fields with hydrogen sulphide (H2S) occur. The Main Dolomite (Ca2), in which H2S-containing natural gas has accumulated, is younger than the Zechstein Limestone (Ca1), which is actively mined. The Ca2 and Ca1 formations are separated by a thick anhydrite succession including a wedge-shaped salt body. Hydrochemical analyses of 18 groundwater samples taken from different horizons within the Zechstein strata showed spatial variability of H2S and chloride concentrations. A conceptual model of groundwater flow with dissolved H2S in the Zechstein formations was developed. H2S migration is associated with groundwater flow between the Ca2 and Ca1 aquifers through fissures in the anhydrite strata that separate them. Hydraulic contact through fissures in the anhydrite layers is the result of long-term exploitation of the underground copper deposit. Groundwater flow between the layers is influenced by a large change in the piezometric pressure of the groundwater in the depression cone caused by mining drainage.
In order to provide a better characterization of the origin and volume of thermogenic gas generation hydrous pyrolysis (HP) experiments were performed on coals and shales at 330 and 360oC for 72 hours. The maturity range of coals and shales used for HP varies from 0.57 to 0.92% Ro. The maturity increase caused by HP at 330 and 360oC ranges from 1.32 to 1.39% and from 1.71 to 1.83%, respectively. δ13C of CH4, 2H6, C3H6 and n-C4H10 in HP gases versus their reciprocal C-number have a concave relationship, and therefore do not follow a linear trend. δ2H of CH4, 2H6 and C3H6 in HP gases versus their reciprocal H-number show both linear and convex-concave relationships. The growth of CO2 yields during HP was higher for shales than for coals. H2S yields from shales are higher than from coals, which can be connected with catalytic and adsorbed influence of shale matrix. H2 was also generated in notable quantities from water and organic matter of coals and bigger amounts from shales. N2 yields grow with the increase of Ro after 3oC HP and it is more enriched in 15N isotope than after 330C.
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