东营凹陷北部陡坡带丰1扇背斜的特征、成因及其与油气的关系

Sedimentary features,genesis and relation to hydrocarbon of fan-anticline in the North Slope of the Dongying Sag

东营凹陷北部陡坡带在沙河街组三-四段沉积时期堆积了很厚的砂砾质碎屑沉积物,发育扇背斜,成为油气聚集的重要场所,近期的油气勘探证明了这一点。扇背斜有别于一般意义上的构造背斜、滚动背斜和披覆背斜,它是一种由低位沉积扇体(包括坡积扇、洪积扇和冲积扇)形成的主体,尔后被高位体系域形成的细碎屑沉积物覆盖而形成的背斜;是砂砾岩体堆积后,其上又由盖层覆盖而成的背斜。虽同为沉积背斜,扇背斜与披覆背斜有很多不同之处。扇背斜油藏本质上是一种岩性油藏,其成藏条件受控于砂砾岩扇体的特性、距油源的距离、砂砾岩扇体和油源之间的连通性以及砂砾岩扇体上覆盖层的封堵能力。该类型的油气藏大多发育在断陷湖盆的陡坡带区域。

The Dongying Sag is one of the most conspicuous petroleum generative depressions in East China. Much clastic deposit of glutenite accumulated and became an important place of hydrocarbon accumulation in the 3rd and 4th Members, Shahejie Formation in the North Slope of the Dongying Sag. Many fan-anticlines composed of sediments of the 3rd and 4th Member developed along the steep slope of the North Slope. Fan-anticline, as a sedimentogenic one, was different from general structural anticline. When glutenite accumulated and was covered by seal,the fan-anticlines were built up. Although the drape anticline is also a sedimentary one,it is different from fan-anticline in many respects. There are 3 genetic types of fan-anticline mainly,including, overriding of turbidite fan, near bank subaquatic fan and fan formed by differential compaction of glutenite. In the Well Fengshen 1 ,the drape trap was based on bossy basement,which lies in the middle part of the North Slope of the Dongying Sag. The drilling revealed that the fan-anticline reservoir was a kind of lithologic reservoir, controlled by the distance and connectedness between glutenite and oil sources, and the shut off capacity of seals. Most of these fan-anticline reservoirs occurred in region of steep slope belt in downfaulted lacustrine basin.