塔里木盆地塔中地区天然气成因及其差异

Origins of natural gas in Tazhong area,the Tarim Basin and their differences

通过对塔中天然气组分和碳同位素地球化学特征的系统分析，发现塔中天然气气态烃组分基本上呈正碳同位素系列，δ^13C1〈-30‰，为有机成因烷烃气。通过ln（C2／C3）-ln（C1／C2）关系及参数C2／iC4与C2／C3关系的研究，认为奥陶系天然气属原油裂解成因天然气；石炭系天然气既有干酪根裂解气，也有原油裂解气。塔中东、西部不同的烃源岩和成熟度导致塔中东、西部天然气组分和碳同位素存在显著差别，西部天然气主要来源于中一上奥陶统烃源岩，东部天然气可能主要来自高-过成熟的寒武系烃源岩。硫酸盐热化学还原作用在区域上存在强弱之分，偏东部井区较西部井区强。

A systematic analysis is conducted on compositions and geochemical characteristics of carbon isotopes of natural gas in the Tazhong area, Tarim Basin. It is found that the gaseous hydrocarbon compositions of the natural gas from the Tazhong area basically show a pattern of δ^13C1〈δ^13C2〈δ^13C3 〈δ^13C4 with their values of δ^13C1 all below -30%o,indicating their organic origin. According to the relationship between ln（ C2/C3 ） and In （C1/C2 ） and that between C2/iC4 and C2/C3 ,natural gas in the Ordovician is believed to originate from pyrolysis of crude oil. While natural gas in the Carboniferous is mixed gas originating from pyrolysis of both kerogen and crude oil. In the eastern and western parts of the Tazhong area, the source rocks are different in age and thermal history, leading to the significant differences of hydrocarbon compositions and carbon isotopes of natural gas in these areas. In the western part, natural gas mainly originates from the Middle-Upper Ordovieian source rocks. While in the eastern part, natural gas probably originates from the high-to over-mature Cambrian source rocks. Thermochemical sulfate reduction in the eastern wellblock is stronger than that in the western wellblock.