摘要
利用天然气地化识别技术研究了莺歌海盆地浅层天然气生物降解及混源特征.研究结果表明,该区天然气遭受生物降解后,除正构烷烃浓度降低、被降解组分碳同位素变重外,在降解作用微弱的天然气中还检测出生物成因的烯烃.在莺歌海盆地中央泥底辟带,存在母质类型相似、但处于不同演化阶段的多套气源岩,具有生成不同成熟度天然气的物质基础.该区普遍存在由生物气(或低成熟气)与热成因气(有的已被生物降解)混合而成的混合天然气,泥拱活动产生的(微)裂隙为天然气运移及混合提供了主要通道.随气藏埋深变浅,生物气(或低成熟气)的比例增大,混合天然气的δ13C1变轻.由于生物降解作用将热成因气中的CO2转化为甲烷,混合作用补充了富烃的新烃气(生物气和低成熟气),从而改善了热成因气的品质,有利于该区富烃天然气的形成.
In Yinggehai basin, biodegradation and mixed sources of shallow gasfields can be studied by using the geochemical recognition technology. When natural gas is biodegraded by bacterial activity in this basin, its concentration of normal alkane components will reduce and the δ 13 C value of biodegraded components will become heavier. Meanwhile biogenetic alkene components can be detected in the biodegraded gas. In the central mud_diapir area of Yinggehai basin, there are several sets of gas source rocks with a similar type of kerogen and different maturity, providing a matter basis for generating gas with various maturity. The gas mixed by biogenic gas (immature gas) and thermogenic gas (sometimes biodegaraded) occurs widely, and the fractures and microfractures induced by mud_diapir have served as important conduits of gas migration and mixing. Furthermore, the content of biogenic gas will increase and the δ 13 C value of methane will lighten in the mixed gas as gasfields become shallower. Because CO 2 can be transformed into methane during biodegradation and new hydrocarbon gas (biogenic gas or immature gas) will join in the original thermogenic gas by mixing, the quality of gas in reservoir may be improved, which is favorable to accumulation of hydrocarbon_rich gas in the area.
出处
《中国海上油气（地质）》
2002年第3期189-195,共7页
China Offshore Oil and Gas(Geology)
