The Study On The Prediction Methods Of Reservoir Parameters And Thin Layer Thickness For The Continental Shale In The Jianghan Basin

As a typical continental salt lake basin,Qianjiang Sag,a secondary tectonic unit in the middle of Jianghan Basin,is an important oil-rich sag.Among them,Qianjiang Formation in Qianjiang depression developed a set of salt series strata with huge thickness of salt rhythm sand-mudstone.The target strata of this paper are mudstone,dolomitic shale and calcareous mirmirite strata interbedded with salt rock.This set of stratigraphic units has high oil content and good mobility,which has good exploration and development prospects in continental shale oil field.However,seismic identification and description of intersalt shale oil reservoir still face challenges.Firstly,the microstructure of shale affects the enrichment,migration and hydraulic fracturing of shale oil.Therefore,it is necessary to study forward and inversion of rock physics on the basis of clarifying the rock physical mechanism to predict the microscopic structure of shale reservoir.Secondly,the prediction of oil and gas enrichment degree is an important problem in the prediction of shale oil reservoir "sweet spot".Due to the small difference in physical properties of oil and water in reservoir fluids,it is necessary to carry out oil-bearing prediction based on rock physical modeling of shale oil reservoir.In addition,it is necessary to predict the thin reservoir thickness under the background of intersalt shale oil rhythm to clarify the basic geological structure of thin shale oil reservoir.Therefore,this article between shale oil reservoirs in Jianghan Basin salt based on the study of the geological structure and rock physical mechanism,to carry out the shale oil rhythm reservoirs between salt rock physics modeling and seismic inversion,microcosmic physical parameters to predict shale oil reservoir,oil content,key reservoir parameters such as thin layer thickness,provides critical information for shale oil dessert zone.At first,this article for qianjiang formation of Jianghan Basin shale formation between the salt rock physics model was constructed,based on rock physical model inversion method to predict shale borehole micro physical parameters and the anisotropic parameters,and to develop salt based on rock physics model and neural network algorithm between shale oil reservoir physical property parameters of seismic inversion technique.The elastic and inelastic anisotropy characteristics of shale from micro to macro structure are quantitatively characterized by rock physical model,including the inherent anisotropy related to clay mixture and the additional anisotropy caused by horizontal fractures.Based on the illite/montmorillonite ratio and intergranular soft matter content,the clay mixture model was established to consider the anisotropy of the layered superimposed structure of illite/montmorillonite particles and intergranular soft matter.Petrophysical inversion shows that the microscopic physical properties and structural parameters of shale reservoir have obvious vertical heterogeneity,and the content and distribution of illite are the main controlling factors of the overall anisotropy of shale.Rock physics inversion can predict the anisotropy of shale solid matrix,which can reflect the development of horizontal bedding and contribute to the evaluation of reservoir mechanical properties.The calculated horizontal fracture parameters can provide a reference for reservoir evaluation and fracability evaluation.The predicted global anisotropy parameters of shale can provide more accurate velocity models for seismic forward,inversion and imaging techniques.Based on borehole rock physical inversion result,established by the neural network algorithm of petrophysical parameters and seismic attributes nonlinear quantitative relationship,for quantitative interpretation of the seismic elastic inversion results,get between salt laminated shale oil reservoir structure,physical property parameters,such as horizontal seam,and the spatial distribution of anisotropic parameters,provide favorable reservoir identification and description of the methods and techniques.Secondly,the seismic oil and gas identification method can be used to predict the potential oil reservoir in the shale in the study area.However,due to the similar elastic properties of oil-bearing shale and water-bearing shale,it is difficult to identify shale with high oil saturation.In addition,the elastic response of organic-rich shale is more complicated due to the complex mineral composition and organic matter properties,which further increases the difficulty of applying elastic properties to seismic characterization of shale oil reservoir.However,if the inelastic properties associated with enrichment of organic matter and hydrocarbons in shale are considered,the dispersion properties of seismic waves provide a new method for hydrocarbon identification.In this paper,a seismic inversion method is proposed to directly estimate oil saturation using fluid dispersion properties sensitive to oil and gas enrichment.This method extends the traditional seismic frequency-varying AVO inversion method by introducing the approximate formula of p-P wave reflection coefficient expressed by equivalent pore fluid volume modulus.Then,a petrophysical model of shale oil reservoir was developed to describe velocity dispersion and attenuation associated with organic matter and hydrocarbon enrichment.The rock physics simulation results show that the dispersion properties of fluid volume modulus related to frequency are more sensitive to oil saturation than the velocity dispersion properties of shale as a whole.Combined with the proposed shale physical model and the synthetic data of high-precision seismic forward modeling,the seismic dispersion inversion method proposed in this paper is verified by theoretical model.The analysis shows that compared with the traditional p-wave velocity dispersion attribute,the fluid volume modulus dispersion attribute proposed in this paper is more sensitive to oil saturation.The application of actual data of intersalt shale oil reservoir in Jianghan Basin verifies the practicability of this method in oil-bearing prediction of intersalt shale oil reservoir.Finally,the geological structure of intersalt shale oil reservoir in Jianghan Basin is rhythmically thin interbedded.Due to the limitation of seismic resolution,conventional seismic theory based on tuning effect is difficult to accurately predict the thin intersalt shale oil reservoir thickness.In this paper,a seismic method based on waveform is established to predict the thickness of rhythmic shale thin layer.Firstly,based on the selected logging data,the geological and geophysical model of the target layer is designed under the background of the actual rhythmic structure.For each well,consider the possibility of shale speed and thickness of thin layers,the changes of transmission matrix method is used to calculate the metrical structure by a thin layer of shale parameters such as velocity,thickness change of seismic response,to establish the prediction model of thin layer thickness of space,by looking for the actual seismic reflection wave and seismic wave form the best match in model space to predict shale thin layer thickness,The spatial distribution of shale thin reservoir thickness is obtained.There is a high consistency between the predicted thickness in well location and the logging interpretation results,which verifies the effectiveness of the method presented in this paper.Combining the thin shale thickness predicted by this method with the reservoir physical property parameters predicted by seismic petrophysics,it can provide a basis for comprehensive description of favorable shale oil reservoirs.