Multi-scale high order finite different reverse time migration imaging

Xiaodan Zhang,Lei Zhu,Hua Guo

doi:10.1186/s13640-018-0290-x

Abstract

At present, the main difficulties in oil and gas exploration are focused on the exploration of the deep region. How to improve the efficiency of imaging on the same accuracy of migration is an urgent problem. The paper puts forward the concept of multi-scale grid for the underground medium based on finite difference time domain (FDTD) of reverse time migration (RTM), which can avoid the oversampling to high speed and hold the sampling density to low-speed layer. The method can shorten the time of RTM with the same accuracy of the traditional RTM imaging. Firstly, devise the multi-scale grid model according to the velocity model; it uses the small-scale grid for the low-speed area and large-scale grid for high-speed area; secondly, calculate the value of each point of the wave field on multi-scale model, especially the points of transition zone; finally, image the underground media according to the RTM imaging condition. The experimental results show that under the condition of the same simulation order, the multi-scale RTM imaging computational efficiency can be promoted by 25.05% average within this paper.

Highlights

In recent years, along with the oil and gas, reservoirs of traditional and simple structure have been mined gradually; the discovery of mineral resources becomes more difficulty and it makes the resources which can be protected and properly used without any way
The two scales of the grid are employed for this model, and the design idea is that the dx = 5m and dz = 2.5m are used to the first layer which is the small step in Z direction, and the dx = 5m and dz = 5m are used to the second layer which is the bigger step than the first layer in Z direction; the step of the X direction stays the same
The wave field forward modeling is performed on the model, and the shot’s coordinates are 50 m and 75 m, the time interval is 0.5 ms, the snapshot of wave field when t = 30 ms used multi-scale method is shown in Fig. 5, and in Fig. 6 is the result of traditional method

Summary

Introduction

Along with the oil and gas, reservoirs of traditional and simple structure have been mined gradually; the discovery of mineral resources becomes more difficulty and it makes the resources which can be protected and properly used without any way. The RTM algorithm is studied in order to achieve a balance between the improving computing efficiency and the imaging precision.

Results

Conclusion