南海神狐海域试采区天然气水合物精细速度建模方法

RESEARCH AND APPLICATION OF FINE VELOCITY MODELING TO GAS HYDRATE TESTING DEVELOPMENT IN THE SHENHU AREA OF SOUTH CHINA SEA

底辟、高角度的断裂、滑塌等构造在南海神狐海域广泛发育,它们为天然气水合物的形成提供了良好的流体运移通道。为了提高试采区内天然气水合物地震数据的成像精度,尤其是断层及断裂结构的成像精度,开展了一套专门针对天然气水合物的精细速度模型构建方法,初始速度模型建立以CVI约束速度反演为基础,通过时间偏移域内剩余速度分析与拾取方法进行初始速度模型优化,采用基于层速度的弯曲射线叠前时间偏移来提高信噪比,在初始速度模型优化的基础之上,以剩余曲率法为基础的层析速度反演来完成深度域层速度的迭代与更新,最后通过叠前深度偏移实现试采区天然气水合物精细地震成像。通过对南海神狐海域试采区的实际应用结果表明:BSR的连续性更好;波组特征更加明显,同相轴连续性增强,利于解释人员进行层序划分;复杂构造成像清晰,有明显的强反射特征,底辟构造成像清晰;浅层小断层更加清楚,层间反射清晰,大断面归位合理,细节更清楚;能为新的成藏模式及现场钻井风险提示提供必要的数据依据。

In the Shenhu area of the South China Sea,widely developed are diapirs,high angle fractures and slumping structures,which have provided channels for gas hydrate migration.In order to improve the imaging precision of natural gas hydrate in the area,especially the image accuracy of faults and fractures,a set of technology for precise construction of a velocity model is developed.The initial velocity model is established on CVI constrained velocity inversion.Then it is optimized by residual velocity analysis and pick-up method in time migration domain.Bending ray pre-stack time migration based on interval velocity is used to improve the signal-to-noise ratio.After optimization of the initial velocity model,high precision grid tomography velocity inversion on the basis of residual curvature method is adopted to complete internal velocity iteration and updating in the depth domain.Finally,fine seismic imaging of gas hydrate is realized by pre-stack depth migration.The practical application of the method to the Shenhu trial mining area in South China Sea suggests that the imaging accuracy in the fault zone is much improved,the description of fault system becomes clearer,the wave group characteristics are obviously improved,and the signal-to-noise ratio and resolution of seismic data are improved greatly.From the data,it is not difficult to find out that BSR is getting better in continuity;wave group characteristics become much clear,seismic event continuity is enhanced and good for sequence stratigraphic division;the imaging precision of the fault zone is obviously improved,fracture structure becomes more clearly,and the signal-to-noise ratio and resolution are improve.The dataset is more qualified to provide a solid basis for new reservoir modeling and field drilling risk evaluation.