Analysis Of Seismic Response For Heterogeneous Carbonate Reservoir

Carbonate reservoirs in my country are characterized by diverse types,complex spatial distribution,and strong heterogeneity.Strong heterogeneity causes complex seismic wavefield changes,making it difficult to establish seismic identification models and have poor quantitative prediction accuracy.Seismic physical simulation can more realistically reflect the wave propagation characteristics in the forward simulation of complex reservoirs,and is often used to study the seismic wave characteristics of reservoirs.Therefore,for the high-velocity body heterogeneity that may appear in the strata,as well as the thin interbedded dolomite reservoirs,platform margin shoal facies reservoirs and fault-karst reservoirs in Sichuan and Xinjiang.The petrophysical research of high-velocity heterogeneous bodies,and the seismic wavefield and attribute analysis of three types of carbonate reservoirs related to the actual area are carried out using the seismic physical model technology.The heterogeneous scale and velocity have a greater impact on the characteristics of seismic wave propagation in heterogeneous reservoirs.In this study,the pulse transmission method was used to record measurements at the ultrasonic frequencies of2.25,1,and 0.5 MHz through a set of low-content(10%)variable-scale high-velocity heterogeneous samples.The relationship between P-wave field features and heterogeneity scale,P-wave velocity,and the multiple of the wavenumber and heterogeneous scale ka was observed in the laboratory.Experiments have found that when a pulse wave propagates in a three-dimensional high-velocity heterogeneous medium,its propagation characteristics are different from that of low-velocity heterogeneous medium,and its wave field changes are more complicated.The waveform,amplitude,and velocity of recorded P-waves correlate with the heterogeneous scale.For the forward scattering while large-scale heterogeneities,noticeable direct and diffracted waves are observed in the laboratory,which indicates that the influence of direct and diffracted waves cannot be ignored for large-scale heterogeneities.There is no velocity inflection point when large angle scatter is converted to forward to scatter.The relationship between velocity and ka shows frequency dependence;the reason is that the magnitude of change in velocity caused by wavenumber is different from that caused by heterogeneous scale.According to the change in the recorded waveform,amplitude variation,or the relationship between the velocity measured at different frequencies and the heterogeneous scale,the identified turning points of the ray approximation are all around ka =10.When ka is less than 1,the velocity changes slowly and gradually approaches the effective medium velocity.The ray velocity measured for heterogeneous media with large velocity perturbations in the laboratory is significantly smaller than the velocity predicted by the perturbation theory.For the thin interbedded dolomite reservoirs,laboratory comparative analysis of high-frequency seismic data and conventional seismic data was carried out.Studies have shown that conventional seismic data can only identify thin interbedded reservoirs with specific structures;for high-frequency seismic data with a seismic wavelet frequency of60 Hz,thin interbedded reservoirs can be identified by amplitude and waveform.At the same time,the ability of seismic coda to predict and monitor thin dolomite reservoirs is analyzed.The study shows that the coda time migration has nothing to do with the frequency change of the wave,and the change of the reservoir causes the obvious coda time migration.For the reservoir prediction,it can be seen that the coda change of the high frequency data can reflect the thin reservoir of changes in position and velocity.The coda waveforms recorded by conventional data are basically the same,and the energy difference is small,making it difficult to use for reservoir prediction.For platform margin shoal facies reservoirs controlled by sedimentary structure,the research results show that the seismic attribute analysis technology based on large time windows for platform margin shoal reservoirs cannot accurately describe the changes of sedimentary microfacies.According to geological models,accurate stratum interpretation of focused reservoirs can accurately describe seismic facies zones;reservoir parameters affect amplitude.Reservoirs with large sedimentary thickness and good physical properties have stronger positive amplitudes;amplitude attributes can intuitively identify the physical properties of reef-shoal reservoirs,while frequency attributes have a strong ability to identify reservoir boundaries.Based on the data of the fault-karst reservoir physical model,the seismic response characteristics of the main strike-slip fault and the secondary fault are summarized.The tensional segment of strike-slip fault has a negative flower-like structure with weak internal reflection energy and obvious dislocations.The compressional segment of strikeslip fault has an obvious positive flower-like structure,with chaotic strong reflection inside.The translational segment of strike-slip fault appears as a linear anomaly.When the heterogeneity of the secondary inner fault is strong,a beaded reflection will be formed at the top and bottom interfaces of the fracture,and the beaded reflection at the top interface is stronger than that at the bottom interface.The seismic response characteristics of caves and fractured reservoirs controlled by strike-slip faults are mainly characterized by three types: “fault + beaded reflection”,“fault + linear weak reflection”,and “fault +plate strong reflection”.The ability of coherence and maximum likelihood attribute to identify faults is compared and analyzed.The results show that the maximum likelihood attribute has a clearer fault combination relationship on the plane and has a better effect on fault identification.