Seismic Modeling And AVO(Amplitude Variation With Offset) Analysis Of Carbonate Cavernous Reservoirs

String of beads,called SBR,are typical seismic responses for carbonate cavernous reservoirs in Tarim Basin.Understanding the corresponding relationship between SBR and cavernous reservoirs and achieving fluid identification play important roles in local prospecting and exploration.They have been urgent demands for local geophysicists.To demonstrate the seismic responses of these reservoirs better,seismic physical and numerical modeling experiments are conducted.Based on the seismic data,the corresponding relationship between different types of cavernous reservoirs and SBRs is established and the SBRs and AVO responses for reservoir saturated with different fluids are analyzed.Seismic properties are obtained from seismic inversion and crossploting analysis is conducted to discriminate fluids.First,through seismic physical modeling,the corresponding relationship between six types of SBRs,short SBRs,long SBRs,chop-shaped SBRs,inclined SBRs,waved SBRs,and chaotic SBRs,and their potential cavernous reservoirs is established.It is indicated that SBR depends on two factors,reservoir scale and spatial distribution of multiple caves.Second,seismic physical and numerical modelings show reservoir scale is an important factor for AVO.AVO intercept,or amplitude at zero offset,increases first and then decreases with reservoir width and thickness.Crossploting analysis shows the reservoir change,both the width and thickness,gives a rise to a spiraling effect on AVO intercept-gradient crossplot.Samples move in an anticlockwise direction along with the reservoir scale increase.Third,the fluid impacts on SBRs and AVO are studied through seismic physical modeling.The estimated seismic velocity increases with the water saturation and is less than the velocity from ultrasonic measurements.Besides,transducer directivity correction is conducted to obtain accurate AVO.It is indicated reservoirs with different fluids exhibit different AVOs.Due to the impact of reservoir scale,there are clear discrepancies between the real AVO and the theoretical AVO from Zoeppritz equations of cavernous resevoirs.At last,based on the seismic data from physical modeling experiment,seismic inversion is conducted to obtain seismic properties.Crossploting analysis is applied to achieve fluid discrimination.The result shows it is viable to achieve fluid discrimination for cavernous reservoirs through seismic properties crossploting analysis.It is indicated that crossplotting of Zs-?,??-?,and ??-? shows the best identification result.