Imaging Research On Reverse Time Migration Approach For VSP Data

With the increasing complexity of exploration targets,the search for remaining oil and gas resources needs to increase the exploration depth of target,while facing thin and subtle reservoirs.Therefore,it is urgent to apply the new technology of seismic exploration,carry out high-resolution seismic exploration,and realize the accurate imaging of complex underground structure.As an important component of reservoir geophysical technology,VSP(Vertical Seismic Profiling)technology plays an important role in the exploration and development of oilfield with its high resolution and high information volume.VSP can obtain the data volume around the well with the conventional ground source,effectively identify the well next to the fault,thereby improving the reservoir description accuracy.Compared with the traditional raybased Kirchhoff typed and one-way wave equation method,the reverse time migration method based on the two-way wave equation has more imaging accurate.For this reason,the reverse time migration of VSP seismic exploration data has great significance to the description of the surrounding layers and deep structure subface.In this thesis,we study the computation accuracy,computation efficiency,storage,noise and absorption attenuation boundary of VSP reverse time migration imaging algorithm.The main research progress is as follows:(1)Based on the optimization of finite difference wave field simulation and reverse time migration,we proposed a further one-step wave field simulation and reverse time migration imaging method.With this method,we could obtain wave field with high precision,no dispersion effect,strong stability.The reverse time migration based on one-step method could characterize the underground structure clearer;(2)The variable order finite difference method,the double-buffer storage strategy,the damped random boundary and the effective boundary with PML(Perfectly Matched Layer)are proposed,which could greatly reduce the wave field storage of reverse time migration;(3)The method of optimizing the non-local mean denoising method is proposed to effectively suppress the random noise and the arc noise of VSP reverse time migration.The proposed method could also improve the accuracy of the reverse time migration result based on random boundary condition;(4)The least squares reverse time migration method is proposed to improve the imaging resolution of the conventional exploration and VSP seismic data effectively;(5)The multi-thread and multi-GPU parallel acceleration technology is proposed to accelerate the least squares reverse time migration imaging method.The multi-GPU cooperative segmentation calculation of 3D wave field is completed,which improves the adaptability of GPU equipment to large-scale data,The implementation of data input and output operations with mult-thread processes,reducing the algorithm delay effect;(6)The reverse time migration imaging tests was carried out for the simulated seismic data of Walkaway VSP and 3D VSP and the actual data from one oil area.