Research And Application Of AVO Inversion Method Based On Petrophysical Analysis

With the advancement of oil and gas exploration technology,lithologic reservoirs have become one of the main targets of exploration.The Triassic Baiguowan Formation clastic reservoir and the Ordovician Dajing Formation carbonate reservoir in the Xichang Basin have a relatively intact sedimentary environment.But the conventional inversion method can not meet the requirements of exploration accuracy because of the fault system develops and the heterogeneity is strong.AVO technology predicts oil and gas according to the change of amplitude with offset or incident angle,which has strict theoretical basis,and can effectively identify highlights.Petrophysics is the link between reservoir physical parameters and elastic parameters.The rock physics analysis and AVO inversion method are effectively combined to establish a rock physics model,to perform shear wave estimation.And it can establish a model based on fluid replacement,to invert elastic parameters and analyze the characteristics of fluid and AVO.The intended purpose is to identifying rock properties and hydrocarbon-bearing characteristics by finding the elastic parameters of each reservoir segment which are sensitive to the characteristics of oil and gas.The shear wave velocity has a great influence on the accuracy of elastic parameter inversion and fluid detection.Based on the theory of petrophysics,the matrix modulus can obtained by Xu-White model,and could corrected by log reconstruction.The fine shear wave velocity suitable for AVO inversion and analysis can be obtained.The rock physics model is established by fluid replacement,and the shear wave estimation method is studied.The rock elastic parameters and AVO characteristics are combined to improve the oil layer identification ability.It's purpose is better use the seismic data to identify the hydrocarbon content of the reservoir.Based on the characteristics of the heterogeneity of the study area,this paper uses the adaptive grid ray tracing method to obtain the incident angle and travel time of the seismic wave.The Zoeppritz equation also be choosed to accurately obtain the amplitude to synthesize the angle gather.Combined with AVO forward modeling and fluid substitution model,the AVO effect of different fluid states has been analyzed.It was found that the Yimen Formation,Baiguowan Formation and Dagu Formation had three seismic anomalies.The Triassic Baiguowan Formation was determined by amplitude curve analysis.The AVO reflection characteristics of the rock reservoir show a third type of gas,and the carbonate reservoirs of the Ordovician Datun Formation exhibit the first type of gas-bearing characteristics.And we establish corresponding detection marks by the characteristic.By pre-processing of the pre-stack gathers,the data body which can reflect the amplitude variation with the incident angle could be obtained.And then the elastic impedance inversion is performed by combining the data body and the physics angle analysis.By analyzing the elastic parameter profiles such as longitudinal and transverse wave velocity,density,longitudinal and transverse wave velocity ratio and Poisson's ratio,the sensitive parameters was be found.Poisson's ratio and gradient property are the sensitive parameters of the clastic rock section,and the longitudinal and transverse wave impedance reflectivity of the carbonate rock segment.Then we can identify lithology and predict gas of reservoir by the analysis of sensitive parameters.