杭州湾地区浅层气成藏条件分析

Reservoir Formation Condition of Shallow Gas in the Area of Hangzhou Bay

杭州湾地区浅层天然气主要赋存于第四纪全新世和晚更新世地层中。气样组分分析表明 ,该区天然气属甲烷型生物成因气。有机地球化学分析表明 ,生物气气源层具强 较强的还原环境 ,同时具有较高的有机质丰度、较好的有机质类型等有利条件 ,而持续沉降、快速沉积作用和有利的沉积环境是生物气形成的重要地质条件。良好的储盖条件有利于浅层气的聚集和保存 ,结合钻井资料可知 ,该区储气层以细砂为主 ,由于埋藏浅、时代新、岩石疏松、未固结成岩 ,构成了良好的储集层。本区第四纪全新世主要生气层为近岸浅海相、受海侵影响的河漫滩相和河口湾相的灰、灰黑色淤泥质亚粘土、粉砂质粘土与亚粘土 ,系良好的区域盖层。

The shallow gas in the Area of Hangzhou Bay mainly exists in the Holocene and late Pleistocene of Quaternary. According to component analysis, it is methane type biogas . Organic geochemical shows that the biogas source bed has strong or relatively strong reducing environment and rich ,good-typed organic matter. The continuance sedimentation, speedy sediment and good sedimentary environment are the important geology factors to forming shallow gas. Favorable reservoir and seal conditions are conductive to its congregation and conservation. In the light of drilling data we can know that, the favorable reservoir rock layer in this area is mainly built up by fine sandstone, and it has the character of shallow concealed, new era, loose and unconcretion. On the other hand in this area there is good region seal-rock , the Holocene of Quaternary's sub-clay is the main seal-rock in this area.