Deep Cracked Reservoir Forward Modeling And Reflectivity Analysis

With the long-term exploration and development of middle and shallow fields,most of them are entering in late stage of development,while facing the growing demand for oil and gas resources,extending oil and gas exploration to the deep and ultra-deep field has become an inevitable trend.Deep reservoirs tend to have low porosity and permeability characteristics,and aligned fractures are migration channels for the low-permeability reservoir.Therefore,fractures are closely related to the improvement of these reservoirs,which makes the fractured reservoir become the focus of today's seismic exploration.Fracture detection by seismic is based on the seismic properties of fractured medium.Seismic responses of fractured reservoir show anisotropy,and medium with high-angle fractures can be equivalent to an HTI medium according to the anisotropic theory.Seismic forward modeling is to simulate seismic wave propagation in the Earth's medium,and to study the relationship between seismic wave propagation characteristics of the Earth's medium parameters.Numerical seismic forward modeling possesses great theoretical significance and practical value in correctly understanding seismic wave propagation,verifying the correctness of the earth model,geological interpretation and reservoir prediction etc.Firstly,the forward modeling method based on reflectivity theory with a case study in the acoustic wave equation is introduced.Then solutions for some problems in reflectivity forward modeling are provided,which achieve good results.Then reflectivity method for 2D elastic wave equation under the Cartesian coordinate system is introduced.3D seismic forward modeling of anisotropic medium is necessary to study the azimuthal anisotropic characteristics of fractured reservoir,thus 3D elastic wave reflectivity method under the Cartesian coordinate system is derived.Based on a 2D elastic wave reflectivity forward modeling theory,the reflected wave energy characteristics of the isotropic deep reservoir are studied,besides,the effect of the deep of the target zone and strong reflected interface on the AVO are analyzed.A fractured reservoir rock physics model is established,based on which a 3D reflectivity forward modeling is carried out,then azimuthal reflection characteristics of the fractured deep reservoir is analyzed and discussed.Finally,pre-stack seismic inversion of the deep reservoir is conducted using reflectivity forward modeling operator based on modified genetic algorithm.The tests result show that the modified genetic optimization algorithm has better global search capability,thus reaching better inversion results.