Carbon isotopes of Middle–Lower Jurassic coal-derived alkane gases from the major basins of northwestern China |
| |
| Authors: | Jinxing Dai Caineng Zou Jian Li Yunyan Ni Guoyi Hu Xiaobao Zhang Quanyou Liu Chun Yang Anping Hu |
| |
| Institution: | aPetroChina Research Institute of Petroleum Exploration and Development, Beijing 100083, China;bDepartment of Earth Science, Zhejiang University, Hangzhou 310027, China;cFaculty of Natural Resources and Information Technology, University of Petroleum, Beijing, 102200, China;dPetroChina Research Institute of Petroleum Exploration and Development-Langfang Branch, Hebei 065007, China;eLanzhou Institute of Geology, CAS, Lanzhou 730000, China |
| |
| Abstract: | Coal-derived hydrocarbons from Middle–Lower Jurassic coal-bearing strata in northwestern China are distributed in the Tarim, Junggar, Qaidam, and Turpan-Harmi basins. The former three basins are dominated by coal-derived gas fields, distributed in Cretaceous and Tertiary strata. Turpan-Harmi basin is characterized by coal-derived oil fields which occur in the coal measures. Based on analysis of gas components and carbon isotopic compositions from these basins, three conclusions are drawn in this contribution: 1) Alkane gases with reservoirs of coal measures have no carbon isotopic reversal, whereas alkane gases with reservoirs not of coal measures the extent of carbon isotopic reversal increases with increasing maturity; 2) Coal-derived alkane gases with high δ13C values are found in the Tarim and Qaidam basins (δ13C1: − 19.0 to − 29.9‰; δ13C2: − 18.8 to − 27.1‰), and those with lowest δ13C values occur in the Turpan-Harmi and Junggar basins (δ13C1: − 40.1 to − 44.0‰; δ13C2: − 24.7 to − 27.9‰); and 3) Individual specific carbon isotopic compositions of light hydrocarbons (C5–8) in the coal-derived gases are lower than those in the oil-associated gases. The discovered carbon isotopic reversal of coal-derived gases is caused by isotopic fractionation during migration and secondary alteration. The high and low carbon isotopic values of coal-derived gases in China may have some significance on global natural gas research, especially the low carbon isotope value of methane may provide some information for early thermogenic gases. Coal-derived methane typically has much heavier δ13C than that of oil-associated methane, and this can be used for gas–source rock correlation. The heavy carbon isotope of coal-derived ethane is a common phenomenon in China and it shed lights on the discrimination of gas origin. Since most giant gas fields are of coal-derived origin, comparative studies on coal-derived and oil-associated gases have great significance on future natural gas exploration in the world. |
| |
| Keywords: | Coal-derived alkane gases Middle– Lower Jurassic coal-bearing strata Carbon isotopes Light hydrocarbons China |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
