| As the unconventional oil and gas resource,the demand for shale oil and gas exploration and development technology is gradually increasing,and geophysical exploration technology is the core of shale oil and gas resources evaluation.Shale reservoirs have complex microscopic physical characteristics and macroscopic anisotropy characteristics,which are of great significance for the study of geophysical methods of shale reservoirs.In this paper,the rock physics and seismic methods are studied and discussed for dense shale reservoirs with low porosity and low permeability characteristics,which provides a method for the development of geophysical logging and seismic evaluation,reservoir identification and description technology in shale reservoirs.Quantitative seismic interpretation based on seismic inversion method is one of the main development directions of shale reservoir description at present.Therefore,in the study of the exploration methods of shale oil and gas reservoirs,based on rock physics and using seismic forward and inversion methods as effective geophysical tools,the related qualitative seismic analysis and quantitative seismic interpretation research can provide abundant geophysical information and basis for the identification and description of shale oil and gas reservoirs.It is of great significance for the improvement and promotion of geophysical exploration methods.The shale reservoir includes shale gas reservoir and shale oil reservoir,the inherent anisotropy and horizontal layer development of shale reservoir make the reservoir present VTI(vertical transversely isotropy)anisotropy,and the difference of microstructure characteristics causes a variety of macroscopic anisotropy characteristics.Firstly,rock physics method and seismic method are studied for the microscopic physical characteristics of shale gas reservoirs with VTI anisotropy characteristics,in order to provide a basis for the description of shale dessert area by predicting the physical parameters of shale gas reservoirs.Taking the shale gas reservoir in Longma group as an example,this paper establishes the physical model of VTI Anisotropic rock,carries on the rock physical inversion in reservoir physical parameter well based on the model,and applies the inversion result to the quantitative interpretation of seismic elastic parameters under the framework of BP neural network,and gets the spatial distribution of reservoir physical parameters,It provides a method and technology for the identification of shale gas reservoir dessert area.Firstly,on the basis of the analysis of the microscopic physical properties of shale,the key physical parameters are abstracted,and the equivalent medium theory is used to model,and the quantitative relationship between the microscopic physical characteristics such as complex mineral components,the properties of the organic mixture of kerogen and fluid composition,the porosity of organic matter and the macroscopic VTI of shale is established.Then,based on the rock physical model design inversion method,the simulated annealing particle swarm algorithm is used to solve the objective function,and the normal logging curve inversion of the reservoir physical parameters such as the aspect ratio of organic matter mixture,the pore degree of organic matter and the anisotropic parameters of shale VTI.Finally,BP neural network method is used to establish the nonlinear mapping relationship between shale physical parameters and elastic parameters,on the basis of which the results of seismic elastic inversion are quantitatively explained,and the spatial distribution of shale physical parameters can be used to further analyze the physical characteristics of shale gas reservoir pore connectivity,shale brittleness,organic matter maturity and gas content,It provides the basis for seismic identification of shale dessert area.In this paper,the physical characteristics of shale oil reservoirs with horizontal seams are further studied,and the anisotropic characterization of shale reservoirs is based on rock physics.As the space of shale oil storage and migration,the horizontal seam in shale oil reservoir affects the VTI characteristics of shale oil reservoir,so the study of horizontal seam characteristics in shale oil reservoir can provide a method for the description of reservoir macroscopic anisotropy and the evaluation of oil production quantity.Based on the study of Anisotropic media in VTI,the AVO inversion algorithm of prestack VTI anisotropic parameters for calculating VTI anisotropy parameters and horizontal seam density is proposed on the basis of the theoretical formula of VTI dielectric reflection coefficient proposed by Rüger,and the inversion algorithm is applied to calculate the shale oil reservoir in Huraud home area.Firstly,by applying the Backus averaging method to the logging data of shale oil reservoirs in Luo family area,the data is coarsely from the logging data scale to the high-resolution seismic exploration data scale,and the anisotropic equivalent model of VTI is established.Then,the anisotropic propagation matrix is applied to the equivalent model for forward simulation,and the seismic AVO response of shale oil reservoirs is obtained,and the comprehensive logging data,synthetic seismic records and actual seismic data are used for well seismic calibration.In this paper,the fitting relationship between VTI anisotropic parameter epsilon and horizontal seam densityε_H is calculated by using the AVO inversion method of anisotropic parameters of Prestack VTI,combined with the results of rock physical inversion calculated by predecessors,in order to calculate the spatial distribution of horizontal seam in the study area and compare it with the actual oil and gas data,and prove the effectiveness of the inversion method.The spatial distribution of horizontal seam is calculated by using the AVO inversion method of Prestack VTI anisotropic parameter proposed in this paper,which provides a basis for the description of shale oil reservoir and the prediction of oil and gas yield.Considering the vertical cracks in the shale oil reservoir,an orthogonal anisotropic equivalent medium model is established,and the azimuth information is introduced to simulate the seismic response simulation of the whole wave field.The anisotropic reflectivity method is simplified by introducing the horizontal slowness,and the seismic AVAZ(amplitude versus azimuth)response of the orthogonal anisotropic equivalent medium model is calculated,and the characteristics of the vertical cracks and their influence on the azimuth anisotropy characteristics are analyzed in combination with the model.Firstly,two orthogonal anisotropic equivalent models with different anisotropy characteristics of the overlying layer are established,and the forward simulation is carried out by using the simplified anisotropic reflectivity method,and the influence of the anisotropy characteristics of the overlying layer on the anisotropic characteristics of the seismic response is discussed by analyzing the seismic AVAZ response and azimuth amplitude distribution of two models.Then,a rock physical model is established for the shale oil reservoir in the Luo family area of Jiyang depression.Because of the vertical cracks in the VTI background of shale reservoirs,the reservoir has equivalent orthogonal anisotropy characteristics,and the equivalent orthogonal anisotropic medium is used as the model.Using Backus average theory,the VTI anisotropy of logging data scale is coarse to the high resolution seismic exploration data scale,and the vertical crack is introduced by using Schoenberg theory,and the orthogonal anisotropic equivalent medium model is obtained.After that,the anisotropic reflectivity method is used to simulate the full wave field seismic inversion of the established model,the AVAZ response is calculated,and the reservoir cracks are described by the azimuth characteristics of the amplitude.By analyzing the variation characteristics of the azimuth amplitude response of PP wave,PSV wave and PSH wave and the fitting shape of azimuth amplitude distribution map,the development direction of the crack is judged,which provides the basis for the seismic method identification of cracks in shale oil reservoir. |
PDF Full Text Request