莺歌海盆地生物气成藏特征

对莺歌海盆地第四系-上新统生物气的地球化学特征、气源岩生烃潜力、成藏条件等进行综合分析，发现该区生物气以甲烷和氮气为主,干燥系数高达0.99，甲烷碳同位素轻（-74.7‰～-55.72‰）,但氢同位素偏重；认为该区第四纪-上新世快速沉积造就了甲烷形成的有利地质环境，该套气源岩平均有机碳含量约0.4%，平均产甲烷潜量达278 m³/t（有机碳），显示出较大的生气潜力；烃源岩内部不连续砂体比较发育；盖层厚度大、渗透性差且饱和高矿化度地层水,使得其排替压力明显小于下伏砂岩，对气层产生了有效的封盖作用。因此，该区上新统-第四系具有适合于生物气的生成、运聚成藏的地质-地化条件，勘探前景广阔。

CHARACTERISTICS OF BIOGAS RESERVOIR FORMATION IN YINGGEHAI BASIN

The geochemical characteristics, source rock hydrocarbon potential, reservoiring condition of the Quaternary System—Paleocene Series in Yinggehai Basin are comprehensively analyzed to clear the biogas reservoiring characteristics and exploration prospects. It is discovered that the biogas are mainly methane and nitrogen with a dry coefficient of 0.99, a lighter methane carbon isotopic values (－74.7%—－55.72%) and a heavy hydrogen isotopic composition. The analysis result shows that the rapid sedimentation of the Quaternary—Pliocene in the basin provided a favorable geological condition for the generation of biogenic gases, and the set of marine biogenetic gas source rock has an average total organic carbon value of 0.4% with a total methane yield of 278 m3/t TOC and displays a great biogas potential; there are well developed sand body traps within the marine biogas source rocks; the overlaid muddy rocks saturated with high salinity strata water have a large thickness and a low permeability, which leads to a large capillary pressure in contrast with the sandstone and is qualified to act as a good cap. Therefore, the sequence of Quaternary—Pliocene in Yinggehai basin has favorable condition for the generation, migration, accumulation and preservation of the biogases and is of good exploration prospects.