Geochemistry and occurrence of inorganic gas accumulations in Chinese sedimentary basins

Inorganic gases are commonly seen in eastern China and occasionally in southern China from the shallow water columns above hot and cold springs. The gases contain 68% to nearly 100% CO2, with delta C-13(CO2), and delta C-13(1) values in the range of -1.18 parts per thousand. to -6.00 parts per thousand and -19.487 parts per thousand to -24.94 parts per thousand, respectively. All of the 34 large inorganic CO2 and one inorganic methane accumulations discovered in China are distributed in eastern parts of the country, from both onshore and continental shelf basins. No commercial inorganic gas accumulation has been found in central and western China. This is a review of the occurrence and geochemical characteristics of inorganic gas accumulations in Chinese sedimentary basins. A detailed study of gas samples collected from four representative inorganic CO2 pools and one possible inorganic methane pool indicates that inorganic alkane gases typically show delta C-13(1) values greater than -10 parts per thousand. versus PDB (mostly >= -30 parts per thousand), with a positive stable carbon isotope sequence of delta C-13(1) < delta C-13(2) < delta C-13(3) < delta C-13(4). In contrast, the delta C-13(1) values of biogenic alkane gases are lighter than -30 parts per thousand, with a negative isotope sequence (i.e. delta C-13(1) > delta C-13(2) > delta C-13(3) > delta C-13(4)). Inorganic gases also tend to show less negative delta C-13(CO2), values (>= -10 parts per thousand) than biogenic gases (< -10 parts per thousand). (c) 2005 Elsevier Ltd. All rights reserved.