Study On Reverse Time Migration Methods In Complex Media Of Borehole Seismic

In order to solve the fine imaging problems of borehole seismic technology in complex reservoirs,unconventionality and marine oil and gas exploration,the wave equation method is used to study the full wavefield forward numerical simulation and reverse time migration imaging of borehole seismic.The borehole seismic exploration has the characteristics of detection close to the target,which is able to obtain the geophysical attributes that can directly reflect the geologic formation,oil reservoir or target body.Its accuracy and detection range are the spatial expansion and effective supplement of surface seismic and logging methods.In the forward modeling study of borehole seismic wave equation,considering the propagation characteristics of seismic wave in complex media,starting from the wave propagation theory,the specific expressions of acoustic wave,visco-acoustic wave,elastic wave equation of viscoelastic media are given,and the corresponding staggered-grid finite-difference scheme of first-order velocity-stress wave equation under different media are deduced.The forward modeling method of borehole seismic wave equation is discussed in detail in term of source loading,absorption boundary conditions,medium type and geometry system.The model simulation tests show that the finite-difference wave equation forward modeling method of borehole seismic studied in this paper can effectively simulate the full wavefield propagation characteristics for different complex media.At the same time,the elastic wavefield separation algorithm is considered in the forward modeling,which provides a theoretical basis for the complex medium wavefield separation processing and converted wave imaging.In the research of borehole seismic reverse time migration imaging,the influence of boundary conditions,imaging conditions and migration artifacts on imaging results is mainly discussed.The demonstration scheme design method of borehole seismic reverse time migration geometry system based on field acquisition requirements is mainly studied,and the following results are obtained:(1)based on the finite difference wave equation forward modeling method of the complex medium in borehole seismic,this paper proposes a reverse time migration algorithm in complex medium that is suitable for the borehole seismic geometry system;(2)combining ray forward modeling and reverse time migration imaging,a design method of the imaging target-driven is improved for borehole seismic field acquisition geometry;(3)according to the method of Open MP parallel programming,the parallel computation of borehole seismic wave equation reverse time migration in complex media is realized in the Linux environment,which greatly improves the computing efficiency.Theoretical model and actual data inversion show that the reverse time migration imaging technology of borehole seismic can accurately image the complex media and structures,and has high computational efficiency;(4)a complete design method of borehole seismic field acquisition scheme and borehole seismic data reverse time migration imaging technology are developed based on the actual needs of borehole seismic exploration.The borehole seismic reverse time migration method is used to demonstrate the field acquisition scheme in an actual offshore well area,which effectively makes up for the lack of seismic wave dynamics characteristics of the ray-based method in designing the geometry system,helps the final data acquisition to achieve better exploration results,and later the method is used in imaging the real data.Compared with the surface seismic imaging results,the reverse time migration not only solves the problem of insufficient resolution of offshore 3-D surface seismic,but also provides a new idea for fine imaging of small structures.The main innovative achievements in this work mainly included:(1)combining forward modeling(ray tracing)and reverse time migration imaging,a design method of the imaging target-driven is improved for borehole seismic field acquisition geometry;(2)based on the actual needs of borehole seismic exploration,a borehole seismic data reverse time migration imaging technology are developed.