和田河气田天然气东西部差异及原因

The difference in geochemical characteristics of natural gases between eastern and western parts in Hetianhe gas field of Tarim basin and its origin

塔里木盆地和田河气田天然气是成熟度较高的干气 ,二氧化碳和氮气含量高。天然气来自寒武系海相高—过成熟烃源岩 ,属油型气。气田呈近东西向展布 ,西部井区的埋深小于东部井区 ,西部井区天然气二氧化碳含量和干燥系数明显高于东部 ,西部井区甲烷碳同位素重于东部。导致东西部天然气的地球化学特征有明显差别的原因是 ,天然气自东向西运移造成了组分的东西部差异 ;西部井区的压力释放使水中溶解的CO2 大量释放 ,导致CO2 含量增加 ;扩散作用导致了甲烷碳同位素的西重东轻。

Based on the study of geochemical characteristics of natural gases of Hetianhe gas field in Tarim basin and in combination with the analysis of source rocks and geological conditions, it is concluded that the alkane gases in Hetianhe gas field is high maturing dry gases with high content of CO 2 and N 2. The gases are of oil type, which are generated from high over mature Cambrian source rock. Hetianhe gas field distributes mainly from east to west like a belt. The buried gas layer of the field's western part is shallower than that of eastern part. The geochemical characteristics of natural gases are different between the eastern and the western parts. Compared to the eastern part, the natural gases in the western part have more CO 2 content; and the dry coefficient is higher; Carbon isotope of methane is heavier. The reasons that cause the differences of geochemical characteristics of natural gases between the western and eastern parts in Hetianhe gas field are as follows: the gases migrated from east to west in the gas field and caused the different component of natural gas; the pressure became lower in western part of the field caused the dissolved CO 2 releasing from water, thus the CO 2 content became higher; methane could easily disperse through cap rocks in western part made the methane isotope became heavier.