Carbon isotopes of Middle-Lower Jurassic coal-derived alkane gases from the major basins of northwestern China
Carbon isotopes of Middle-Lower Jurassic coal-derived alkane gases from the major basins of northwestern China
复制标题
DOI：
10.1016/j.coal.2009.08.007
复制
发表时间：
2009-11-01
影响因子：
5.6
通讯作者：
Hu, Anping
中科院分区：
文献类型：
--
作者：
Dai, Jinxing;Zou, Caineng;Hu, Anping
中国西北地区中下侏罗统含煤地层煤成烃主要分布在塔里木、准噶尔、柴达木和吐哈盆地。前三个盆地以煤成气田为主，分布于白垩系和第三系地层中。吐哈盆地是一个以煤成油气田为特征的盆地。通过对这些盆地的天然气组分和碳同位素组成的分析，本文得出了三个结论：1）含煤岩系的烷烃气不存在碳同位素反转，而含非煤岩系的烷烃气随着成熟度的增加，其碳同位素反转程度增加; 2）在塔里木盆地和柴达木盆地发现了高δ C-13值的煤成烷烃气（δ C-13（1）：-19.0~-29.9ppm; δ C-13（2）：-18.8~-27.1ppm），最低的δ C-13值出现在吐哈盆地和准噶尔盆地（δ C-13（1）：-40.1~-44.0ppm; δ C-13（2）：-24.7~-27.9ppm）; 3）煤成气中轻烃（C5-8）的个别碳同位素组成低于油伴生气。煤成气的碳同位素反转是由运移和次生蚀变过程中的同位素分馏作用引起的。中国煤成气的高、低碳同位素值对全球天然气研究具有一定意义，特别是甲烷的低碳同位素值可能为早期热成因气提供信息。煤成甲烷的δ C-13通常比油伴生甲烷的δ C-13重得多，这可用于气源岩对比。煤成乙烷的重碳同位素在中国是一个普遍现象，它对天然气成因的判别具有重要意义。大气田多为煤成气，开展煤成气与油成气的对比研究对今后世界天然气勘探具有重要意义。(C)2009 Elsevier B.V.保留所有权利。
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 delta C-13 values are found in the Tarim and Qaidam basins (delta C-13(1): -19.0 to -29.9 parts per thousand; delta C-13(2): -18.8 to -27.1 parts per thousand), and those with lowest delta C-13 values occur in the Turpan-Harmi and Junggar basins (delta C-13(1): -40.1 to -44.0 parts per thousand; delta C-13(2): -24.7 to -27.9 parts per thousand); 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 delta C-13 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. (C) 2009 Elsevier B.V. All rights reserved.