Seismic Wave Impedance Inversion And Its Application In Carbonate Reservoir Prediction

Carbonate reservoir is an important oil and gas producer which holds at least a half of total resource in the word. The main production layer of the most mid-large oil and gas fields is carbonate reservoir. In general, carbonate reservoir has a high heterogeneity and many types, which is controlled by the sedimentary environment and diagenesis. These features greatly increase the difficulty of reservoir prediction. The wave impedance inversion can calculate the wave impedance of target stratum using well logs and seismic data. Then the difference of wave impedance between the reservoir and surrounding rock can be used to identify the reservoir. So the wave impedance inversion is one of few methods which play an active role to carbonate reservoir prediction. The carbonate reservoir of Xiaoquan-Xinchang Trap, Western Sichuan is very thin and has a low resolution on seismic data. In this case, the conventional wave impedance inversion methods, such as constrained sparse spike Inversion, cannot accurately reveal the difference of difference of wave impedance between the reservoir and surrounding rock. Therefore, the stochastic inversion based on geostatistics is introduced into carbonate reservoir prediction in this paper.Stochastic inversion which based on geostatistics can get a group of equiprobable parameter model of reservoir by stochastic simulation on spatial distribution pattern, correlation and physical parameter justified by faulted framework, well logs and seismic data. This method uses the spatial distribution pattern(histogram) and correlation(variogram) from known data to obtain the parameter model of reservoir which meets the well logs and seismic data. The information of wave impedance and lithology which have higher resolution and are more suitable to geologic feature than conventional inversion methods can be obtained by quantitative analysis on indeterminacy.This paper mainly studies the practical applications of constrained sparse spike inversion and stochastic inversion. First of all, it introduces the present situation and development trend of seismic wave impedance inversion; it studies in detail the basic theory, classification and the limitations of different inversion technique in wave impedance inversion; Then, by the characteristics of carbonate reservoir in western Sichuan areas, chosen the constrained sparse pulse inversion and stochastic seismic inversion based on geostatistics, in-depth study and analysis the principle, the key technology of the two methods(including seismic and well data processing, wavelet extraction and synthetic seismogram, initial model establishment, the quality monitoring of inversion, etc.; and stochastic seismic inversion in geostatistics used in the probability density function and variation function) and the characteristics of their respective advantages; finally, with InverTrace-plus module of constrained sparse spike inversion and StatMod MC module to simulate of stochastic seismic and geostatistics stochastic inversion in Jason inversion software. In the process of inversion, the inversion parameters are very important. Through the inversion result, can be roughly range to the reservoir description and prediction.The results of two inversion methods are contrasted in practical applications by analyzing the main influencing factor. The result of stochastic inversion overcomes the modeling phenomenon,and have a higher resolution.