| On one hand, with the growing shortage of oil and gas resources, fracture typereservoirs are becoming the focus of the oil and gas exploration and developmentgradually. As a result, the study of fracture attributes of the reservoir stratum would bepaid more attention to; On the other hand, because the influence of fracture is crucialfor dams, bridges, highways and buildings, the detection and evaluation of fractureattributes is an important goal of geophysical prospecting.In every field of science and technology, simulations could be divided into twobroad categories: numerical simulation and physical simulation. Both of thesesimulations are a kind of basic research work in the field of seismic exploration.Numerical simulation has the characteristics of flexible, fast and economic, whilephysical simulation is another kind of intuitional and effective method. Therefore, welaunched simulations experiment in two kinds of wave field (electromagnetic waveand ultrasonic wave). Finally, the results of two kinds of simulation methods would becompared and conjoint analysis.The propagation of seismic waves in fractured medium may exhibit anisotropy,especially shear wave. Share wave splitting phenomenon would occur. We can usethis phenomenon to identify the azimuth and the density of fractures. First, weconducted two-dimensional three-component seismic wave numerical simulationsbased on the HTI medium model using numerical simulation. Second, we use twoforms, seismic recording and snapshot of the wave field, to simulate the regulations ofshear-wave splitting with the varied fracture densities and angles between measuringline and fracture orientation. Then we conducted numerical simulation as the anglebetween measuring line and fracture orientation is45°, fracture density is0.1 including x-component and y-component, and used the Pearson correlation coefficientmethod of predecessors to calculate the fracture azimuth angle and fracture density,the results we acquired is very accurate. At the same time，we designed an HTI mediamodel with magnetic and electrical conductivity differences, and conducted3D-FDTD numerical simulations. Then we acquired different component data ofpolarimetric ground penetrating radar (GPR), and calculated the changes of themaximum amplitude value ratio with the crack azimuth angle varied, and made atemplate. At last we conducted numerical simulation as the angle between measuringline and fracture orientation is45°, and the result of fracture azimuth angle weacquired is more accurate than the method of seismic wave.We also conducted physical simulations using the same HTI media model. Thefirst is the production of the physical model, according to the principle of geometricsimilarity ratio, we designed HTI media model as the ratio of1:10000to thegeological model and we used the plexiglass plate as the skeleton part of crack andusing paper as cracks section. During the seismic physical simulation, we used anultrasonic single transducer to transmit and receive ultrasonic waves for simulatingthe propagation of seismic waves in the subsurface media, and we also analyzed themeasured results using the Pearson correlation coefficient method and we found theresult is more desirable. GPR is now a well-accepted geophysical technique. Themethod uses radio waves to probe “the ground” which means any low loss dielectricmaterial. Use the way of rapid, continuous non-detection and have fast acquisitionspeed and high resolution. We conducted physical simulation using the same modeland inverse the fracture azimuth angle using the same method as numerical simulation,but the deviation is a little larger.Finally, a joint analysis of these two kinds of wave field simulation methods hasbeen given at the end of this article. It is proved by the result that joint inversion ofthese two methods is more accurate than single method inversion in getting fractureazimuth. Seismic wave and electromagnetic wave are both effective in detectingfracture and analysing fracture attributes. Each of these methods has its advantage.Seismic wave simulation could not only get the information of fracture azimuth, but also can obtain the information of fracture density. However, the information offracture azimuth which obtained by seismic wave simulation could hardly as accurateas the one obtained by ground penetrating radar. Therefore, joint detection could be aneffective method to enhance the accuracy of seismic exploration. The study of thesetwo kinds of wave field simulation could be a foundation of the future joint inversion. |
PDF Full Text Request