塔河油田油气成因和运移的氦同位素证据

HELIUM ISOTOPIC EVIDENCE FOR HYDROCARBON GENERATION AND MIGRATION IN TAHE OILFIELD

塔里木盆地塔河油田是目前我国在海相碳酸盐岩层系中发现的最大油田。为明确勘探方向和目标，通过测试该油田原油伴生气的氦同位素组成，探讨了该油田的油气成因和运移问题。研究结果表明，该油田原油伴生气的^3He／^4He比值分布在2．99×10^-8～8．27×10^-8之间，平均为4．89×10^-8；R／Rn比值为0．02～0．06，平均为0．035。这反映了壳源成因特征，说明该油田油气在形成和运移聚集过程中缺乏地幔流体的参与。该油田原油伴生气中氦同位素组成在区域分布上具有一定的规律性，研究认为这种分布特征起因于油气运移过程中伴生气的扩散作用和水、油溶解作用的氦同位素分馏，因而氦同位素组成及其分布特征可能是一种可以表征油气运移情况的新指标。据此指标揭示出该油田的油气由南向北运移，说明油气主要来自该油田南部满加尔坳陷及其邻近地区的烃源岩区。

Tahe oilfield in the Tarim Basin is the largest oilfield discovered in the marine carbonate sequences in China so far. In order to determine future exploration directions and targets, the hydrocarbon generation and migration of this oilfield are studied through testing the helium isotopic components of the associated gas. The 3He/4He ratio of the associated gas is in the range from 2. 99×10-8 to 8. 27×10-8, averaging at 4. 89*10-8. The R/Ra ratio ranges from 0. 02 to 0. 06, averaging at 0. 035. This reveals that the hydrocarbons are of crustal origin and no mantle fluids are involvement during hydrocarbon generation and migration in this oilfield. The helium isotopic components of the associated gas in this oilfield show certain regularity in their regional distribution, which may be resulted from diffusional effects of the associated gas in the process of hydrocarbon migration and helium isotopic fractionation caused by oil dissolution. Therefore, helium isotopic components and its distribution features may be new indicators of hydrocarbon migration. These indicators show that hydrocarbon migration is from south to north in this oilfield, indicating that the hydrocarbons are mainly sourced from Mangar Depression and its adjacent areas in the southern part of this oilfield.