南海北部白云凹陷深水油气区的重-震数据处理与分析

白云凹陷位于南海北部陆缘深水地带,是我国深水油气资源勘探的重要地区。开展重-震成像研究,是分析该区烃源岩分布特征、大型构造圈闭、成藏层系与储层条件的重要方法。本文通过重力异常、地震Vs波速结构模型及地震勘探剖面分析,获得研究区自由空间重力异常、布格重力异常、水平和垂向梯度、密度反演图像、Vs波速度结构图像以及高分辨率地震勘探剖面图像。重力图像揭示:白云凹陷中心的强负值异常图像与较厚沉积和基底起伏有关;凹陷东侧相对高正值局部重力圈闭与中生代残余地层有关;凹陷北侧条带状正异常则与陆坡向洋盆过渡时基底下凹有关。白云凹陷的主凹陷和南凹陷存在明显的层状负剩余密度或相对低密度区,是有利的含油气层位。地震图像揭示:白云凹陷由北向南存在明显的细颈化带、外缘隆起带、洋陆过渡带等结构。在陆缘地壳强烈伸展薄化期间,白云凹陷形成大型三角洲-湖相烃源岩沉积环境的凹陷结构,沉积物源主体来自北侧。随着地壳强烈减薄的细颈化,凹陷出现明显的台阶式沉陷,导致陆架坡折带由南向北迁移,形成陆架边缘三角洲、深水重力流水道和深水扇等有利的储层。高分辨率地震资料获取的地震勘探剖面图像上,可以识别出许多浅层气运移通道,表明白云凹陷丰富的中、浅层气大多来源于深部地层。 

The Analysis and Gravity-Seismic Imaging in the Baiyun Sag Deep-water Hydrocarbon Area in the Northern South China Sea

Baiyun sag, located in the marginal deepwater area of northern south China sea, is an important area for deepwater oil and gas exploration in China. The gravity-seismic imaging is the important methods to analyze the characteristics of the hydrocarbon source rock distribution, large structural trap, oil and gas accumulation and reservoir formation conditions. In this paper, through the calculation of gravity and gravity gradient inversion, and the analysis of the structure model of the seismic wave velocity Vs and seismic section, the free space gravity anomaly, bouguer gravity anomaly, horizontal, vertical gradient and density inversion images, the structure image of v wave velocity, high resolution seismic exploration profile image of the study area were achieved. The image of gravity data reveals that the strong negative abnormal in the center of Baiyun sag is associated with thicker deposition, basal ups and downs; the east of the sag is relatively high, related to Mesozoic residual strata; the north of the sag is abnormal as bandings, related to the of the concave-down basement where the slope extends to the oceanic basin. The sag and the south sag exist obviously layered negative residual density or relatively low density area, being the most reservoirs to holding oil and gas. The image of seismic data reveals: thin neck belt, outer edge uplift belt, ocean-land transition zone, and so on from north to south of Baiyun sag. During the epicontinental strong stretching thinning crust, there formed the sag structure of large delta-lacustrine source rocks sedimentary environment, and sediment source mainly comes from the north. As the strong thinning crust thin neck, there was obvious in Baiyun sag, resulting that the shelf slope break belt migrated from south to north to form the reservoirs:shelf edge of delta, deep-water gravity current channel and deep-water fan, and so on. Based on the analysis of high resolution seismic data for seismic section, we can identify many gas migration pathways, showing that shallow gas in Baiyun sag originate from deep strata.