Erdgas in Westsibirien -Ergebnisse transdisziplinärer Forschung in deutsch-russischer Kooperation

The greatest known natural gas accumulations, about one third of the global reserves, are located in the northern part of the West-Siberian Basin which is the largest continental sedimentary basin on Earth. The major portion of the gas is found in Cretaceous (Cenomanian to Aptian) reservoir sands of the Pokur Formation. In the past, various theories and hypotheses - often contradictory - have been developed to explain the origin of the huge gas accumulations. The present study resulted in a model that can explain both timing and development of the gas accumulations in the study area. For this purpose, organic geochemical and isotopic data of a large suite of rock and gas samples were evaluated in the framework of the geology, including the particular hydrogeology of the basin. Based on gas solubility calculations it could be shown that methane-saturated groundwater flowing from north to south in the basin-wide, Cretaceous aquifer could release large volumes of methane upon pressure release caused by the Neogene uplift in the northern part of the basin. Therefore, the compositional and isotopic signatures of the gas result from mixing processes in a large drainage area, including »early-thermogenic« and possibly bacterial gas. In addition to this geological aspect of the research programme, the field-work in the West-Siberian Basin was focused also on the study of environmental aspects, such as the bacteriogenic methane generated in swamps, and the release of methane due to anthropogenic activities in the area. It was shown that the emissions of swamp gas significantly exceed the methane emissions caused by production processes.