Research On Rock Physical Characterization And Quantitative Seismic Interpretation Of Sweet Spots Of Shale Gas Reservoir

The ‘sweet spot' parameters of conventional reservoirs mainly refer to porosity and permeability.The parameters of unconventional reservoirs are relatively complex,including brittleness,organic matter content,maturity,pore pressure,porosity and permeability characteristics,reservoir thickness,in-situ stress,etc.Corresponding seismic resrvoir prediction of shale reservoirs is an important task for shale exploration.However,due to the strong heterogeneity and anisotropy of shale,the current rock physical properties of shale sweet spots are not clear enough.There are large uncertainties and multiple solutions in quantitative seismic prediction.In response to this problem,we have carried out research on shale rock physical analysis and modeling methods,focusing on the development of new seismic reservoir prediction methods for shale brittleness and organic matter content.The shale reservoir has been applied and achieved obvious results in Wufeng-Longmaxi shale reservoir.The main research results can be summarized as follows:(1)The quantitative relationship between the clay content,pore type,organic matter distribution characteristics and anisotropic strength of marine organic-rich shale in southern China was clarified.The study found that: anisotropic strength is positively correlated with clay content;anisotropic strength and organic matter content is negatively correlated,which is completely opposite to the research conclusion of Anisotropic Strength Increases with organic matter contentrepresented by American Bakken Shale;Different pore types contribute differently to anisotropic strength,and the bound water porosity can increase significantly anisotropy while free gas/water pores will reduce the anisotropy.Based on this study,a rock physics modeling workflow suitable for southern organic-rich shale was established.(2)Through rock physical analysis,the differences and uncertainties of the mineral composition brittleness index and elastic parameter brittleness index when evaluating unconventional reservoirs with complex lithology and microstructure are quantitatively described.On this basis,a brittleness evaluation criterion that comprehensively considers rock mineral composition and elastic parameters is proposed,which can better indicate high-quality brittle rock than conventional methods and improve the reliability of brittleness prediction.(3)A statistical rock physics classification method based on geological constraints has been developed.This method introduces Markov random fields into Bayesian classification as a geological spatial constraint on the basis of conventional statistical rock physics technology to improve the accuracy and spatial continuity of seismic interpretation results.The method can be further combined with seismic inversion results to achieve quantitative seismic prediction of shale brittleness.(4)Considering the inherent strong anisotropy of shale,the seismic prediction accuracy of brittleness and organic matter content is improved by introducing anisotropic seismic attributes.This work includes three parts: verification of the improvement of anisotropic characteristics on the sweet spots interpretation ability of isotropic seismic attribute,the accurate inversion of anisotropic seismic attributes,and application of improved statistical petrophysical techniques in(3)to carry out seismic attribute interpretation of brittleness and organic matter content by anisotropic attributes.The comparison of the well-side track and the slice analysis along the horizon verify the accuracy and practicability of the method.