The Analysis and Research of Carbonate Rock Cave Imaging Elements

The main reservoir spaces of carbonate rock are fractures and karst caves. They are always present as “string beads” on seismic profile. In order to study the laws of cave imaging, this paper analyzes the imaging resolution of the karst cave, researches the quantitative relationship between karst cave imaging and overlying strata, SNR, fold, migration velocity and prestack depth migration method through a large number of forward modeling. The results show that:(1) Both vertical and lateral resolution of karst cave follow quarter-wavelength tuning law, we can use thin-bed mechanism to explain the resolution of karst cave;(2) The existence of the karst cave will drop down the overlying strata event, it makes the karst cave expressing as collapse and “non-string beads” feature on the seismic section;(3) High fold and small trace interval(bin size) can improve the energy of string beads, suppress the background noise produced by migration;(4) Prestack migration can improve the SNR of the data, increase the imaging accuracy, especially the low SNR data;(5) When migration velocity is small, the edge of string beads is dropping down, conversely is upturned, the deterioration of imaging quality caused by large velocity is more serious than small;(6) The different migration methods have different imaging results, for low SNR data, people should intend to select the frequency or frequency-wavenumber domain method for karst cave imaging.