渤海湾盆地渤南洼陷沙河街组三段剩余压力梯度与油气分布关系

Relationship between excess pressure gradient and hydrocarbon distribution in the 3rd member of Shahejie Formation in Bonan Sag, Bohai Bay Basin

刘华 李君 冯月琳 郝雪峰 林红梅 袁飞飞

Hua Liu Jun Li Yuelin Feng Xuefeng Hao Hongmei Lin Feifei Yuan

为了量化表征超压对油气运聚和分布的关系，综合利用录井、测井和分析测试等资料，在渤海湾盆地渤南洼陷地层流体压力预测的基础上，计算了沙河街组三段（沙三段）剩余压力梯度，并分析了剩余压力梯度变化规律及其对油气分布的影响。研究发现，渤南洼陷沙三段富含油气且超压普遍发育，深洼带剩余压力较大，剩余压力梯度最高，其次为陡坡带和断阶带，缓坡带剩余压力较小，梯度最低。受超压中心分布的影响，各地区油气运移动力条件及其油气富集空间存在较大差异：超压中心区油气运移动力较强，高剩余压力梯度主要分布于断层附近，油气多富集在渤深4断层附近；近超压中心区砂体侧向输导阻力不同，高剩余压力梯度主要出现在非均质性较强的地层中，剩余压力梯度较低的地区是油气运聚的指向区；而远离超压中心的地区剩余压力较小，油气运移浮力作用明显占主导，剩余压力梯度与油气分布关系不明显。

In order to quantify and characterize the relationship of overpressure with hydrocarbon migration, accumulation and distribution, we took the 3rd member of the Shahejie Formation in the Bonan Sag of the Bohai Bay Basin as an example to study the excess pressure gradient and its variation patterns as well as its influence on hydrocarbon distribution based on fluid pressure prediction and through analyses of logging, geophysical and testing data.The results show that the hydrocarbon-bearing third member is generally over pressurized with the deep sag zone having greater excess pressure and the highest gradient, the steep slope and step-fault zones having moderate excess pressure and gradient, and the gentle slope zone having smaller excess pressure and the lowest gradient.The hydrocarbon migration dynamics and reservoiring capacity of a location in the member are determined by its distance to the overpressure center.For locations right in the overpressure center, the hydrocarbon migration is under strong driving forces, high excess pressure gradients are mainly distributed near faults, and oil and gas mainly accumulate near the Boshen 4 fault; for locations adjacent to the overpressure center where high excess pressure gradient mainly appears in highly heterogeneous formations, oil and gas migrate to areas with low excess pressure gradient through sandbodies with various lateral transport capacities; and for locations far away from the overpressure center, the excess pressure is relatively low and buoyancy stands out as the main driving force for oil and gas migration, and the relationship between the excess pressure gradient and the oil and gas distribution is no longer obvious.

10.11743/ogg20200518