Reflection characteristics of seismic waves of carbonate cave reservoirs and their significance to the oil and gas discovery

Due to the complex diagenesis of carbonate rocks and the long-term evolution of reservoir space, the carbonate cave reservoirs dominated by caves and fractures are of great heterogeneous laterally, which lowers the oil and gas exploration success ratio. Therefore, it is quite necessary to have a better understanding of seismic reflection curve characteristics of carbonate cave reservoirs thus to significantly mitigate the exploration risk. In view of this, elastic wave equations were applied to simulate the seismic reflection waves of different carbonate cave reservoir models. The relationship between the maximum peak amplitude and karst cave size on the forward migration section was also summarized and the related analysis was made of the seismic waveforms. The following findings were made. First, with the enlarging width of caves, the corresponding amplitude is increasing; however, when being larger than the Fresnel zone radius, the cave width has no effect on the amplitude. Second, on the section profile, caves are presented in beaded-like or lamp chops shapes; with the fixed width and height of caves, the larger the superficial area of caves, the higher the amplitude. In conclusion, the maximum peak amplitude of seismic curves contributes a lot to the identification of caves. The successful practice in the TH oil and gas field, northern Tarim Basin, validates that this method is reliable and provides a robust technical support for the discovery of those similar hydrocarbon reservoirs.