Seismic Data Dispersion Study Using Low-frequency Rock Physics

Dispersion is an important research content in seismic wave propagation theory.Many rock physics experimental data,numerical models and real seismic data indicate that fluid-saturated media or reservoirs will cause different degrees of dispersion and attenuation of seismic waves.Dispersion is a parameter that is more sensitive to fluids than seismic wave velocity and seismic amplitude.The dispersion characteristics of seismic data of reservoirs with different rock thickness,different fluid types and different geological structures will be significantly different,so the dispersion can be used as a sign of oil and gas.Therefore,by studying the dispersion characteristics of seismic data under different reservoir conditions can help us with fluid detection and reservoir identification.Seismic rock physics,as a bridge between reservoir characteristics and seismic response characteristics,can obtain the rock density,porosity,permeability,saturation,dispersion and attenuation characteristics when the rock is saturated with different fluids by directly measuring the reservoir rock.The proposed rock physics model also provides a theoretical basis for the existence of the dispersion effect.Based on the techniques of low-frequency rock physics,this paper introduces the dispersion and attenuation characteristics of rock physics into seismic data through forward modeling,and then uses time-frequency analysis techniques to study how the seismic response with this dispersion effect changes and how to directly extract and characterize the dispersion and attenuation from seismic data.Combined with real seismic data and logging data,we analyze the dispersion characteristics of seismic responses of different reservoir modes and find the relationship between dispersion characteristics and hydrocarbon-bearing properties.Provides a reliable basis for direct fluid detection and reservoir identification through the dispersion characteristics of seismic data.The main work and achievements of the thesis are as follows:(1)A simple seismic forward modeling method is proposed.Based on the results of rock physics modeling and experiments,the method can take into account the physical properties of the strata and the stratigraphic structure,so that the forward results are more in line with the actual reservoir conditions.(2)Through the theoretical model,the seismic data dispersion properties are studied in depth.Using the smooth pseudo Wigner-Ville distributed time-frequency analysis method,the relationship between the amplitude,phase and dispersion of the seismic response of the dispersion attenuation model is deeply explored.It is proposed to use the time-frequency spectrum,the amplitude maximum with the frequency curve,the amplitude change rate curve and the phase difference of the seismic data to characterize the dispersion properties.(3)Combined with the real seismic data and logging data of heavy oil reservoir in an oilfield in eastern China,we analyzed the dispersion characteristics of three typical reservoir modes.The models are consistent with the actual geological interpretation results and the development drilling results.Using these features can directly detect the presence of reservoirs of similar geological models through seismic data.