The Research Of Seismic Inversion And Quantitative Interpretation Of Tight Gas Sandstone Reservoir Parameters Based On Rock Physics Model

Tight gas sandstone(TGS)is an essential unconventional oil and gas resource.In recent years,the exploration and development of tight sandstone reservoirs have gradually become one of the research hotspots in oil and gas resources.The Ordos Basin is a favorable area for TGS reservoirs in our country,with abundant natural gas reserves and many high-production gas fields.The tight gas sandstone reservoirs have productive exploration and development potential for Upper Paleozoic strata in the study area.Pore-microfracture structure and gas-bearing properties are critical physical parameters for TGS accumulation.However,the seismic response characteristics corresponding to the above physical parameters have not been fully defined.Therefore,it is necessary to carry out rock physics research on TGS reservoirs and build quantitative seismic interpretation and inversion methods on this basis to identify critical physical parameters,such as pore-microfracture structure and gas saturation,and improve the prediction accuracy of high-quality TGS reservoirs.Based on the clarifying the physical characteristics of TGS reservoirs in the study area,this article conducts the rock physics modeling research of TGS reservoirs and subsequent research in the quantitative seismic interpretation of reservoir physical parameters,seismic identification of pore-microfracture characteristics,and inversion of seismic wave dispersion attribute about gas bearing.The main research contents and results are as follows:Firstly,the analysis of geological and geophysical data in the study area shows that the pore-microfracture structure of the TGS reservoir is complex,and the physical parameters and corresponding elastic properties of reservoirs are affected by the poremicrofracture structure.At the same time,the seismic interpretation of the target layer shows that the structural fluctuation of the local region is relatively flat.The high porepermeability development area of TGS reservoirs is an essential condition for gas accumulation and effective development.The pore-microfracture structure parameter is an important indicator to evaluate the pore-permeability characteristics of TGS reservoirs.Therefore,based on microscopic pore-microfracture structure analysis,this article constructed rock physics models based on the equivalent medium theory.Moreover,the pore-microfracture structure parameters of different rock physics models were compared and analyzed,such as pore aspect ratio(single porosity model),soft pore ratio(double porosity model),and pore aspect ratio variance(multiple porosity model),etc.to characterize the effectiveness of tight sandstone pore-microfracture structure in the study area.Through forward analysis of rock physics,inversion of poremicrofracture structure parameters,and prediction of shear wave velocity using logging data,this article verifies the applicability of the double porosity model and the corresponding soft pore proportion parameter to the tight sandstone in the study area.which lays a rock physics foundation for the subsequent quantitative seismic interpretation of reservoir physical parameters and the seismic identification technology of pore-microfracture characteristics.Furthermore,a calculation method of skeleton elastic modulus of tight sandstone based on pore-microfracture structure parameters is proposed.Compared with the traditional empirical formula,the proposed method considers the effects of mineral composition,porosity,and pore-microfracture structure,which provides an effective approach for estimating elastic parameters of heterogeneous compact rock skeletons.Moreover,it can be further applied to calculate the Biot coefficient,fluid factor,and critical constraint parameters of seismic wave dispersion attribute inversion based on the constraint of rock skeleton parameters.Secondly,this article proposed a quantitative seismic interpretation method based on the rock physics framework applied to predict high-quality TGS reservoirs.Based on the rock physics analysis of logging data,the cumulative thickness of the TGS reservoir is calculated by setting the elastic wave velocity ratio thresholds,which provides an effective method for capturing the seismic elastic properties of the target TGS reservoir.Total porosity is estimated from P-wave impedance using the correlation obtained based on log data analysis to optimize the rock physics template.After that,the multi-parameter three-dimensional rock-physics template was calculated based on the double-porosity model,which characterizes the nonlinear quantitative relationship between elastic parameters and physical parameters.Thus the microfracture porosity and gas saturation were quantitatively interpreted.Then,this article defined the factors according to the above multi-parameter prediction results to evaluate reservoir quality for the TGS reservoir.The results show that gas production exhibits an apparent correlation with the factor considering microfracture porosity,which can effectively predict the spatial distribution of high-quality reservoirs.Moreover,the factor provides a basis for identifying high-quality TGS reservoirs.At the same time,the results show that microfractures have an important impact on the productivity of the TGS reservoir,so it is necessary to explore the Pore-microfracture characteristics identification of the TGS reservoir.Furthermore,this article developed a seismic identification method of poremicrofracture characteristics of TGS reservoirs based on rock physics inversion results.Based on the inversion results of the double-porosity model and pore-microfracture structural parameters,this article constructed the pore-microfracture characteristic parameter of the TGS reservoir to represent the comprehensive influence of high pores and microfractures on the TGS reservoir.Moreover,this article constructed the poremicrofracture characteristic parameter through the correlation analysis of the poremicrofracture characteristic parameter with the linear combination of elastic parameters.This article proposed a new seismic attribute with rock physics implications for identifying the pore-microfracture characteristics of the TGS reservoir in the research area.The calculated results show that the predicted pore-microfracture attribute agrees with the logging permeability,which provides effective information for seismic identification of the high pore-permeability developed area of the TGS reservoir.The method of constructing seismic attributes proposed in this article can provide a reference for developing new seismic attributes for identifying fluids and fractures,etc.Finally,this article proposed an optimized seismic dispersion attribute inversion method based on rock skeleton elastic parameters constraint.The seismic dispersion attribute is an important indicator of reservoir fluid,wherein the elastic parameters of the reservoir skeleton are an important parameter of the frequency-dependent AVO theoretical formula,which affects the stability and accuracy of the inversion results.With the predicted effects of skeleton elastic parameters from logging data based on the rock physics method,this article established the nonlinear mapping relationship between reservoir elastic parameters and skeleton elastic parameters based on the BP neural network method combined with a genetic algorithm.And the nonlinear mapping relationship is applied to predict the spatial distribution of skeleton elastic parameters from seismic data as the constraint parameter of seismic wave dispersion attribute inversion.Compared with the conventional method assuming the skeleton elastic parameter is constant,the proposed method considers the influence factors of the solid matrix and pore structure reflected by the rock skeleton elastic parameter.Therefore,this method can effectively improve the accuracy of fluid prediction,reduce the uncertainty of seismic wave dispersion attribute inversion in the TGS reservoir,and provide a reference for other seismic inversion methods that need to consider the rock skeleton elastic parameters.This paper studies the research of seismic inversion and quantitative interpretation of tight gas sandstone reservoir parameters based on rock physics model.Based on studying the rock physics model,this paper develops the quantitative seismic interpretation method of the TGS reservoir,the seismic identification method of poremicrofracture characteristics of the reservoir,and the inversion method of the seismic wave dispersion attribute based on the constraint of rock skeleton elastic parameters,which provides practical methods for identification of TGS reservoir with gas bearing,high porosity and permeability,and high-quality reservoir.