Research On Rock-physics Modeling And Inversion Methods Based On Pore Structure

Compared with the conventional sandstone rock physics model,the rock physics model of carbonate reservoir is more complex.The main reason is that carbonate rock has complex pore structure,which leads to more complex relationship between seismic response and reservoir physical parameters.Carbonate reservoir shows strong hetero-geneity,and its heterogeneity characteristics lead to a series of urgent problems to be solved in seismic reservoir prediction.Therefore,in the study of seismic reservoir de-scription methods of carbonate reservoirs,it is necessary to strengthen the consideration of the influence of rock pores to effectively improve the accuracy of carbonate reservoir prediction.Considering the carbonate reservoir with complex pore structure,this thesis aims to study rock physics modeling,elastic parameter prediction and prestack seismic inversion around the parameters characterizing pore structure.The pore structure modeling on micro-scale and seismic scale is studied.On the micro scale,two modeling methods for pore structure are introduced,one is the common method based on equivalent pore aspect ratio,and the other is the modeling method of pore aspect ratio distribution function based on velocity-pressure measurement data.This method can better explain the variation characteristics of soft and hard pores with pressure,in which soft pores are the main cause of squirt flow.On the micro scale,the finite element modeling method of the pore structure is also carried out.The forward results show that the parameters of pore structure,such as pore distribution,porosity and pore aspect ratio,are important factors affecting elastic wave propagation,in which the difference of pore distribution and porosity will cause obvious difference of scattering attenuation,while the difference of pore aspect ratio is mainly reflected in the absorption and attenuation of elastic wave.On the seismic scale,a reservoir model containing different pore types is established,and the influence of different pore types on seismic wave reflection amplitude response is analyzed by using the method of plane wave forward modeling,and the relationship between pore types and seismic anisotropy is discussed.The prediction of elastic parameters is carried out by using the method of rock physics modeling.Aiming at the prediction of shear wave velocity in areas with un-known mineral contents,an equivalent matrix modulus estimation method based on two-dimensional particle swarm optimization algorithm is proposed and applied to shear wave prediction to realize the prediction of shear wave velocity in areas with complex lithology.This method shows high computational efficiency and accuracy.The method of elastic parameter prediction based on elastic-electrical joint modeling is studied,and the acoustic properties of rock are estimated by using the chain rule.In the application of laboratory measurement data,the method based on joint modeling has high prediction accuracy,which is better than the prediction results of single elastic modeling.Because of the hard rock framework in carbonate reservoir,a high-precision sparse constrained seismic inversion method is proposed,which is sensitive to weak reflection coefficients.The goal of this method is to quickly minimize the regularization con-straints of_1-2norm.Model results show that the new algorithm is obviously better than traditional methods in sparsity,convergence speed and robustness.In addition,considering the importance of regularization parameter estimation to inversion,an adap-tive regularization parameter selection strategy based on generalized Stein unbiased risk estimation is proposed,and a hybrid strategy method based on this strategy can achieve high-precision seismic inversion.Moreover,according to the characteristics of pore structure in carbonate rocks,a rock physics-driven seismic inversion method for directly estimating pore structure parameters is proposed.By establishing a linearized petrophysical model,this method can directly calculate the reflectivity by using the pore structure parameters.The application results of synthetic data and actual data verify the feasibility of direct inversion.The new approximate equation has a good application prospect in the prediction of complex pore structure reservoirs such as carbonate rocks.