一种新的速度模型及其在深水区低幅构造区域地震数据处理中的应用--以南海某勘探区为例

Exponential Asymptotically Bounded Velocity Model Applied in the Seismic Data Processing in the Low Amplitude and Deep-water Area——Seta target in the southeast of Hainan as an example

介绍了一种新的用于描述在压实砂岩地层中速度随深度逐步增加的速度趋势方法。该方法建立的速度模型受地质条件约束且很稳定;一般海底地形,高孔隙压力突变等不连续区域都能适应;且该方法需要比经典的线性速度模型更少的地层数来描述速度剖面,故能更好的控制横向的连续性。其参数变量少且简单易行,可以用于多种速度分析或反演方法中;比如地震速度层析成像或者约束反演。对该方法的各个参数影响进行了分析评估,模型计算拟合良好。此法用于南海低幅构造地区实际资料表明:拟合得到的速度曲线与测井得到的VSP曲线相近,建立的速度场层位划分清楚,符合地质规律,适用于深水少井区。落实了低幅构造局部构造,清晰地描绘构造细节,为储层预测做出贡献。

A new compacted-sediment, vertical-velocity model that represents the effect of gradually increasing velocities with depth is proposed, it~ also a new representation for the velocity distribution in thick,subsurface-sedi- ment basins normally found below the sea bottom, such as the Gulf of Mexico and south sea of China. In these are- as the velocity gradually increases with depth because of the effect of compaction, and the rate of change is faster in the upper layer and gradually decreases with depth. For a given layer, the asymptotically bounded, exponential ve- locity model is defined by three intuitive parameters as： 1 st, the velocity, 2 nd, its vertical gradient at the top in- terface and 3 rd, an upper-limited velocity value. Time-depth relations, velocity transformations, hyperbolic, and no hyperbolic movements are derived. The entire vertical velocity profile is composed of a set of layers, where the velocity function for each layer is defined by the proposed model. This method provides a basis for describing the subsurface using a smaller number of thick layers rather than using the classical, linear velocity model. The asymp- totically bounded nature of the proposed function allows us to obtain stable and geologically, it can adapt to the common basin and the local anomalies such as high pore pressure. The EAB model enables better control of the lat- eral velocity continuity because of the smaller number of parameters required to describe vertical velocity profiles. Above all, it can be used in many velocity analysis or inversion, such as tomography or constrained velocity inver- sion. The sensitivity of the parameter is analysed and the numerical example is good. The 3D velocity inversion based on EAB velocity model can be distinguished in three types of velocity inversion： 1 st, no velocity discontinui- ties occur at interfaces, 2nd, velocity discontinuities occur at interfaces, 3rd, the discontinuity at the sea bottom and discontinuities along velocity anomaly points. This 3D velocity inversion in the low amplitude structural seismic data in the South Sea of China is applred, it tell that the fitting curve fit in with the VSP curve, and the layers in the velocity field can be see clearly. After all, the geologically and stable EAB model are got. The low amplitude structure can be known, describe the detail of this, and attribute to the reservoir prediction.