Seismic Field Numerical Simulation Of Complex Medium Based On Variable Grids

With the development of the oil seismic exploration, we must not lose sight of themany challenges facing the modern petroleum exploration and have to complete manytasks of geological exploration. In the traditional clastic rock exploration, the target ofexploration has been gradually transformed from simple and large structures tocomplicated and heterogeneous reservoirs, especially for the small fracture structures.Because the tranditional technology of wave field numerical simulation need to usefine grid to improve the accuracy of numerical simulation and suppress numericaldispersion in various heterogeneity reservoirs. It will increase the amount ofcalculation during the numerical simulation and reduce the efficiency of simulation.Therefore,it has not been able to meet the needs of the complex lithology and variousheterogeneity reservoirs. Based on the theory of heterogeneity the development ofseismic wave numerical simulation is very necessary.On the basis of the traditional and conventional staggering-grid numericalsimulation, this paper further improves numerical simulation methods and theadaptability of serious reservoir hererogeneity by using variable grid. The core ofvariable grid is using different grid scale for the different scale geologic body. Thenumerical simulation accuracy and efficiency have been further improved by usingvariable grid. Aimed at the common questions of numerical simulation in theory, thepaper analysed the flaw of the traditional numerical simulation, and the variable gridfinite difference algorithm is put forward. The research content mainly includes thefollowing aspects:1. On the basis of the traditional elastic theory, we deduced the conventionalstaggered grid high-order finite difference method, and analysed the numericaldispersion of the conventional staggered-grid finite difference algorithm. We areanalysis of the main factors influencing the finite difference numerical dispersionrespectively from two aspects of time and space. Their include spatial difference accuracy、seismic wave propagation direction (optimal incident angle)、thenumber of discrete points within a wavelength (cycle) and the vertical andhorizontal grid spacing.2. In the cartesian coordinate system, the traditional staggered grid finite differencealgorithm has the non-balanced problem between numerical dispersion andstability because of using fixed step. Therefore we introduced the variable gridnumerical simulation technology. And this chapter offers important discussion andanalysis for different types of grid discretization. Designing different mediummodels to prove the effectiveness of the variable grid numerical simulation.Furthermore, a staggered-grid high-order finite difference method with oddlyarbitrarily variable spatial grids is introduced. Meantime, we analyzed thesimulation efficiency and precision.3. Based on the theory of the variable grid in the elastic medium, the variable gridnumerical simulation technology is applied to the numerical simulationtechnology of viscoelastic medium. The simulation results of different grid typesis analyzed to study the propagation of seismic wave in viscoelastic medium andthe absorption attenuation of seismic wave. Take the hole viscoelastic mediummodel for example, the numerical results show that it is described precisely thespatial variation of physical properties underground media.4. The traditional elastic numerical simulation technology is usually based on ahomogeneous or layered medium. However, the actual medium is usually thedifferent scale heterogeneous body. According to the principle of statistics, thissection estabblished the random medium to describe the actual heterogeneitymedium, and analysis the propagation rules of seismic wave in different types ofrandom meidium. While the varible grid finite different algorithm is applied to thenumerical simulation of random medium.