Abstract:

The reservoir space of the Ordovician carbonates in Tazhong area,Tarim Basin,is mainly composed of fractures and secondary dissolved pores and cavities,and its seismic responses are bead-like reflections.The fact that the reservoir is covered by surface dunes and buried in depth leads to a relatively low signal-to-noise ratio of seismic data and the poor imaging precision for the reservoir.The oil-water contact is complex in the reservoir,making it hard to effectively identify its features by using post-stack hydrocarbon detection method.These problems have seriously restricted the progress of exploration and development of carbonate reservoirs in this area.In order to address these problems,we conducted research based on high-density seismic data in Tazhong area.As the high-density seismic data have higher signal-to-noise ratio and reservoir imaging precision,they are beneficial to study pre-stack hydrocarbon detection method for fractured-vuggy reservoirs.Firstly,more accurate P and S wave velocity can be worked out by Rock Physics Model.Secondly,AVO forward modeling of oil/gas and water wells is conducted,showing discrepant responses from different wells as a result.Therefore,the AVO attributive analysis technique can be used to identify liquids in carbonate reservoirs.Finally,pre-stack simultaneous inversion technique is used to quantitatively identify fluid types in reservoirs in the research area; The predictions are in turn compared with the results of formation testing,revealing an accuracy of liquid predictionsof 83.3%,which manifests that this method provides effective technical support for improving the success rate of drilling and reducing risks of hydrocarbon exploration.

Key words: rock physics modeling, AVO forward modeling, pre-stack inversion, fractured-vuggy reservoir, carbonate rock, Tarim Basin