The Study On Adaptive Estimation Method Of Equivalent Elastic Modulus Based On Rock Physics

Rock physics is a science that studies the relationship between the rock physical properties and its seismic response,which bridges the reservoir parameters and the rock elastic properties to help us deduce the vertical and horizontal changes of the reservoir properties.Rock physical modeling is the process that using the reservoir parameters to quantify rock properties,then to estimate rock elastic properties.A variable dry rock equivalent model has been established based on the rock physical models in this article.Additionally,considering the properties of the sand-shale reservoir and carbonate reservoir to self-adaptively invert the equivalent elastic moduli and then estimate S-wave velocity through the modified simulated annealing algorithm.The tests using experimental data and well log data confirm that the models are robust and practical.Dry rock frame bulk moduli and shear moduli are important input parameters for S-wave velocity estimation.Based on analyzing of the existing dry rock frame models,equivalent moduli with variable parameters are induced to decouple the set of coupled differential equivalent medium equations to ordinary differential equations,then simplify these equations to get the variable dry rock equivalent model with special shape of inclusions(spheres,needles and coin shaped cracks)and ellipsoid inclusions with arbitral pore aspect ratio.Analysis and test of the VDEM show that the model is flexible and applicable and the dry rock moduli estimated by VDEM are with high accuracy.The VDEM can also be utilized to predict P-and S-wave velocity combined with Gassmann equation.The classical Xu-White model has been modified based on the VDEM by further considering the influence factors.The modified model improves the accuracy and applicability of S-wave velocity estimation through self-adaptively inverting the equivalent elastic moduli by the modified fast simulated annealing algorithm.The modified model is tested by the sand-shale experimental data and well log data.The results show that the modified model is with higher accuracy than the classical Xu-White model,and is more applicable.Carbonate reservoir is one of the important hydrocarbon reservoirs.However,the change of the deposition environment and digenetic process reformed the rock frame and pore space of carbonate reservoir,which produces the scatter in the relationship between velocity and porosity.The intense heterogeneity and complex micro structure of the carbonate reservoir make it more challenge to describe the carbonate reservoir than sand-shale reservoir.Adequate considering the heterogeneity and anisotropy of the carbonate reservoir and based on the previous research result to self-adaptively inverted the equivalent elastic moduli and then predict the S-wave velocity of the carbonate reservoir.The test of the carbonate experiment data and well log data verified the effectiveness of the carbonate model.