Isotopic composition of natural waters of Kuzbass in coalbed methane production areas

Abstract

Relevance. In Kuzbass, a coalbed methane production project is being implemented for the first time in Russia. Formation water extracted together with coalbed methane plays an important role, since it has been in contact with the coal-bearing rocks for a long time, therefore it contains rich geochemical information. Over the period 2002–2022, new isotopic data were accumulated both on the waters of the region coal deposits and on overlying waters, including surface waters. Aim. Based on the material accumulated on the isotopic composition (δD, δ18O, δ13C, 34S, 3H, 14C) of natural waters in coal-bearing areas, create an evolutionary scheme for the formation of waters within the framework of the developed hypothesis on the interaction of water-rock-coal-methane. Objects. River, underground waters of the zone of active water exchange, upper and lower parts of the zone of slow water exchange (extracted together with coalbed methane). Methods. Studies of the isotopic composition of waters were carried out in several laboratories: in the Multielement and Isotope Research Center of the SB RAS, the Technical Branch of the Federal State Unitary Enterprise “SNIIGGIMS”, in the radiocarbon AMS laboratory based on the Center for Collective Use “Cenozoic Geochronology” and in the Pacific Oceanological Institute Far Eastern Branch Russian Academy of Sciences (POI) FEB RAS. Results and conclusions. The paper introduces the data on δD, δ18О, δ13С и δ34S for surface and groundwater in Kuzbass in coalbed methane production areas. It is shown that all the waters under consideration are infiltration based on their isotopic composition (δD and δ18О). The waters of the lower part of the slow water exchange, produced together with coalbed methane, are characterized by a positive oxygen shift and very light hydrogen. A diagram of the evolution of the isotopic composition of water-dissolved carbon in the region has been compiled according to the data obtained. It is noted that the atmospheric source of CO2 is characteristic only of river waters, and only biogenic carbon dioxide is present in groundwater. The wide range of δ13СDIC values of the latter is explained by the varying degrees of participation of light soil carbon dioxide and heavy biochemical carbon dioxide formed during methane formation in the coal seam. The heaviest values are typical for waters produced together with coalbed methane, which is associated with long-term interaction with coal and methane. The time of such interaction was determined using the radiocarbon method: 17–30 thousand years. In areas where coalbed methane is produced, an increase in δ13СDIC values for all natural waters is observed, which requires further study.

Keywords

• surface and ground waters
• coal methane
• stable isotopes of hydrogen
• oxygen
• carbon
• genesis