Abstract: Fluid dynamic monitoring is a key technology for the efficient development of oil and gas reservoirs. 4D seismic can directly image fluid changes and enable 3D spatial fluid dynamic monitoring, and is therefore widely used in the development of deepwater oil and gas fields, thermal recovery of heavy oil, carbon dioxide sequestration. However, mainstream 4D seismic interpretation methods suffer from high ambiguity and poor reliability when characterizing complex fluid changes. To overcome these technical challenges, this study, based on theoretical models and 4D seismic forward modeling and using phase transformation technology, establishes the relationship between 4D seismic response and different fluid changes, proposes 4D seismic fluid change indicators, and achieves dynamic interpretation of complex fluid change patterns and ranges. The new method proposed in this paper was used to interpret the fluid changes in the 4D seismic data of the deepwater P Oilfield in Angola, West Africa. The interpretation results are consistent with production dynamic information. The fluid change interpretation results show that the differences in seepage characteristics of oil, gas, and water, along with reservoir structural features, control the movement paths of gas and water. Effective monitoring of fluid dynamic changes provides a reliable basis for development plan adjustment.

Key words: 4D seismic, forward modeling, fluid change indicator, gas injection wavefront, water injection wavefront, Angola deepwater