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

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.