渤海湾盆地板桥凹陷烃源灶与油气生成

 板桥凹陷在中国东部中新生代湖相盆地独具特色，现今油气藏气油比（GOR）变化范围为300～3000m3/t，大部分属于天然气饱和－超饱和油气藏。 本文首先基于大量岩石热解数据和测井、录井等资料，精细刻划了板桥凹陷烃源灶特征，有效源岩主要位于沙一段和沙三段，主体为II2－III型，有机质丰度为1%～2%的源岩对应的氢指数（HI，干酪根热解烃与总有机碳的比值）在100～300mg/g之间，源岩成熟深度范围约为3600～3800m。在此基础上，计算了沙一段和沙三段源岩的生排烃特征和组分，结果表明，板桥凹陷湖相源岩只有在生烃转化率达到30%左右、镜质体反射率（Ro）达0.8%以上才能实现排烃，沙三段排出烃类GOR超过600m3/t，沙一段排出烃类GOR相对较低，大约为222m3/t，与现今油气藏性质较为一致。中国东部更多的实例剖析表明，源岩的HI0和初始有机质丰度是控制油气藏GOR的关键性因素，板桥凹陷天然气大量聚集成藏归因于腐殖型源岩的存在。

Characteristics of Source Kitchen and Hydrocarbon Generation in Banqiao Sag, Bohaiwan Basin

Banqiao sag is the most exceptional feature of the Mesozoic and Cenozoic lacustrine basins in eastern China. Gas to Oil Ratio(GOR) of the present reservoirs ranges from 300m3/t to 3000m3/t, with most of reservoirs saturated or supersaturated with gas. Based on rock-Eval data and logging data, source kitchen characteristics were evaluated. Effective source rocks chiefly lie in the first and the third members of Shahejie formation, which are of types II2－III. Total organic carbonranges from 1% to 2%, which corresponds to Hydrocarbon Index(HI) of from 200mg/g to 350 mg/g. The mature depth of the source rock is below 3600~3800m. Consequently, characteristics and components of the hydrocarbon generation and expulsion can be calculated. Significant hydrocarbon expulsion begins when the transformation rate is about 30% and vitrinite reflectance is more than 0.8%. GORs of the hydrocarbon expulsion from the first and the third members of Shahejie formation are over 600m3/t and 222m3/t, respectively, which is highly consistent with the property of the present reservoirs. The analyses of more regions in eastern China show that the initial hydrogen index(HIo) and the initial total organic carbon are key factors to control GOR of reservoirs. Most of gases trapped in Banqiao sag are attributed to the humic source rock.