柴达木盆地东部微体化石丰度与天然气源岩

Microfossil Abundance and Natural Gas Source rocks in the Eastern Qaidam Basin

柴达木盆地东部三湖坳陷上新统—第四系自生自储的天然气藏,已成为我国四大天然气产区之一。与柴达木盆地侏罗系、古近系—新近系原油伴生气与凝析气不一样,三湖坳陷生物成因气的气源岩母质主要是浅水湖泊动植物的有机质。在该区诸多门类的生物群落中,具有双壳易于保存为化石的微体动物介形类的丰度,与生物成因气源岩的分布密切相关,介形类化石丰度高低变化基本上反映了气源岩的好坏或有无。本文以三湖坳陷介形类化石丰度纵横向变化,提出了三湖坳陷进一步勘探天然气的方向向坳陷北、东和南部比向西部红三旱四号方向较有利,因为该坳陷西部湖水含盐量太高,介形类等水生生物能生存者不多,生烃母质量少。

The Pliocence-Quaternary System self-source and self-reservoir natural gas reservoir of the Sanhu Depression lie in the east Qaidam Basin that has become one of the biggest four natural gas producing districts. Different from those of petroleum-associated gas and condensate gas produced from Jurassic and Tertiary formations of the Qaidam Basin, most gas source rock of parent materials in biogenic gas from the Sanhu Depression are organic matters of animal and plant in shallow water lake. Among the biotic communities of this area, the microbody Ostracods with bivalve can be preserved easily so their abundances have close relationship with the distribution of biogenic gas source rock. The variation abundance of Ostracods fossils can reflect the quality of gas source rock. Based on the vertical and horizontal variation of Ostracods fossils＇ abundance in the Sanhu Depression, this article points the further exploration aspects： because of the high lake salinity in the west part of the depression, most of hydrobios such as Ostracods can not live, the amount of hydrocarbon parent material is small. For this reason, the north, east and south of the depression are considered more favorable for exploration than west towards Hongxinhan 4.