| Shale reservoir is one of the hottest research fields of geophysical exploration.Seismic rock physics analysis is an important tool to analyze reservoir parameters.As the connecting bridge of seismic elastic information and shale reservoir parameters,seismic rock physics can be divided into forward problems and inverse problems.The forward problem aims to the construction for rock physics model.The inverse problem is for inversion of reservoir parameters.Firstly,in this paper we build the anisotropic rock physics model for shale reservoir,and secondly optimize the inversion algorithm by introducing grid analysis for the inverse problem.Finally,we discuss the anisotropy characteristics of shale reservoir based on inversion results.At the same time,we analyze the hot properties of shale reservoirs: brittleness and select the preferred brittle index equation for shale reservoir by combining with the well and seismic data and achieve the shale reservoir brittleness analysis.The main results of this dissertation can be summarized as follows:(1)The construction of anisotropic rock physics model for shale reservoir.The model focuses on simulation the anisotropy of the shale reservoirs which caused by(1)organic matter enrichment;(2)clay lamination;and(3)the penny pore shape.Model uses SCA+DEM effective theory to simulate kerogen in shale,and introduces a factor(CL)representing the extent of clay lamination,and use the pore aspect ratio to control the non-spherical pore shape in shale.The fine simulation of shale is achieved with different anisotropic causes.(2)Based on shale model we constructed,we introduce the mineral content as the third dimension parameters to build the template of the pore aspect ratio inversion,which is more satisfied with the real situation of the three-dimensional pore aspect ratio compared with the two-dimensional inversion,and the inversion of the pore parameters and give us a better prediction of both P-wave and S-wave velocities by using the inverted aspect ratio.(3)In order to obtain more reservoir physical parameters,this paper constructs the double scanning inversion process and get the pore aspect ratio(?)and lamination factor(CL)indicating pore shape and the extend of clay lamination,respectively.We also predict the anisotropy parameters of reservoir,and discuss the relationship between anisotropy anisotropy parameters and reservoir physical parameters.(4)For inverse problem.In this paper,we introduce the grid analysis method to improve the inversion algorithm for reservoir parameters.The grid analysis method extends the measured logging data as normal distribution and logging error is considered into the inversion algorithm,finally we can obtain the probability density distribution maps of inversion parameters.It can reduced prediction error caused by inaccurate measured values,and improve the credibility of prediction results.Moreover,the pore shape and pore types of shale reservoir is predicted by using our method.(5)We select the existed brittleness index formula and find that prediction accuracy of the brittleness index formula built by the elastic parameters is higher than that based on mineral components.The brittleness index formula based on the Young's modulus and Poisson's ratio is more sensitive for lithological variation;however the formula based on the Lame coefficient is more sensitive to pore fluid.Based on the model,we construct the template of rock physical brittleness and can choose the sensitive parameters.The research shows that shales with low Poisson's ratio,middle or high Young's modulus corresponds to shales with high porosity and high brittleness,which represents the "sweet point" area for shale gas exploitation.Finally,according to the evaluation of brittle shale reservoirs for Longmaxi-Wufeng group in Sichuan basin Southwest China,pre-stack inversion results is well coincide with brittleness analysis results based on logging,which verifies the stability and reliability of our brittleness analysis. |
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