柴达木盆地三湖坳陷浅层生物气成藏模式分析

柴达木盆地三湖地区第四系浅层生物气一直被认为完全是由第四系腐殖型有机质生成的.最新研究结果表明:(1)第四系生物气藏探明储量与源岩条件之间不匹配;(2)高分辨率地震剖面特征表明三湖坳陷气田区域第四系发育了大量的气烟囱;(3)生物气组分特征表明有热成因气混入的可能性;(4)乙烷等重烃气碳同位素特征表明三湖坳陷第四系气藏有腐泥型生物气混入;(5)三湖坳陷上第三系狮子沟组发育偏腐泥型有机质.笔者认为第四系浅层生物气藏的形成机理比较复杂,包括“下生上储”和“自生自储”两种模式,第四系的浅生物气由上第三系狮子沟组生物气与第四系生物气混合而成.

Analysis of the accumulation patterns of the shallow biogenic gas pools in Sanhu Depression, Caidamu Basin

The biogenic gas in Sanhu region has been considered being generated by the Quaternary humic type source rock. But the last research results show that, (1) the proved reserves of Quaternary biogenic gas pools does not match with Quaternary source rock condition; (2) some gas chimneys are found on the high-resolution seismic sections of Sanhu region; (3) the component characteristics of the biogenic gas show that thermo-genic gas is possibly mixed in the Quaternary biogenic gas; (4) the characteristics of the carbon isotope of heavyhydrocarbon gases such as ethane show that sapropelic-type biogenic gas is probabily is mixed in the Quaternary biogenic gas; (5) the sapropelic-type organic matter exists in Neogene Shizigou Formation of Sanhu Depression. Based on the research results above, the authors think that the accumulation mechanism of the Quaternary shallow biogenic gas pools is relatively complicated, there are two accumulation patterns: "down-generation and up-storage" of the biogenic gas of Neogene Shizigou Formation and "self-generation and self-storage" of Quaternary biogenic gas. That is, the shallow biogenic gas in Sanhu area is composed of the biogenic gas of Neogene Shizigou Formation and Quaternary biogenic gas.