Natural sources of methane and carbon dioxide on Sakhalin Island and their role in the formation of ecological gas-geochemical zones

Abstract

Two major groups of the lithosphere sources of methane are distinguished, i.e., the lithosphere sources proper (metamorphism, and serpentinization and spreading zones) and organic fuel deposits in the Earth’s crust. Hydrocarbon deposits, mud volcanoes, geothermal systems, and mineral sources are located on Sakhalin Island. All investigated objects are associated with large tectonic faults: the Yuzhno-Sakhalinsky and Main Pugachiovsky mud volcanoes are controlled by the Central Sakhalin fault; the Shakhterskoe coal deposit is confined to the West Sakhalin fault, while the Daginskaya geothermal system and the studied oil- and-gas fields are associated with the Hokkaido-Sakhalin fault. The authors’ studies of natural gases allow allocating two basic zones on the Sakhalin island with different types of hydrocarbon-carbon dioxide sources: Oil-and-gas (mostly methane; north-east) area and Coal-Gas area (carbon-dioxide-methane; west, south-west). Those areas differ in both chemical and isotope composition of natural gases. Some gashazardous areas have also been identified along tectonic faults, where they are due to gas release on the land surface. The populated localities on Sakhalin are shown to be situated near fault zones; therefore, the problem of gas hazard control is of critical importance.