Application Of Finite Difference Time Domain Method In High Frequency Electromagnetic Wave Logging

Being an important method of electrical logging, electromagnetic wave logging is widely used in Petroleum exploration. On the basis of different frequences, three electromagnetic wave logging methods widely used are Electromagnetic Propagated Resistivity Logging with several mega-hertz operation frequency, Ultrahigh-frequency Electromagnetic Wave Logging with above 200 mega-hertz operation frequency and High-frequency Electromagnetic Wave Logging with some dozens of megaherz operation frequency. Each method has its own advantages and disadvantages. Reservoir bed is distinguished by providing the information about resistivity of formations using Electromagnetic Propagated Resistivity Logging method with several mega-hertz operation frequency. The information of dielectric constant of invaded zone is provided using Ultrahigh-frequency Electromagnetic Wave Logging method with above 200 mega-hertz operation frequency, which has no enough radial investigation depth but has a good vertical resolution. In this paper, 10MHz to 100MHz are used, called High-frequency Electromagnetic Wave Logging method, by which vertical resolution and radial investigation depth are improved.Thus, in this paper, which is aiming at the difficult problem, which needs to be resolved urgently in the china'eastern oil fields such as Daqing, Shengli and Liaohe oil field, using Finite difference time domain method, tightly revolving the core of dielectric constant logging, discusses on improving of algorithm, building of mathematical model and logging responses. And the achievements are obtained as following:1. Based on time domain Maxwell equations, the basic theory of Finite Difference Time Domain of the cartesian coordinates is introduced in detail. The propagation of the electromagnetic wave and the effect of absorbing boundary condition are investigated systematically. And then Finite Difference Time Domain equations and absorbing boundary condition of the cylindrical coordinates are developped. The setting of excitation source is introduced. Numerical stability is discussed. By calculating logging responses in homogeneous medium formation and twolayer jump formation, Numerical solutions are consistent with analytic solutions, which shows that the Finite Difference Time Domain method is an effective tool to compute responses of high frequency electromagnetic wave logging.2. By using representative formation models, it is obtained under a given operation frequency and a given spacing that the effect of borehole radius is small, which we can ignore generally speaking; the more the thickness of target zone is, the less the effect of shoulder beds is; phase shift curves compared with amplitude ratio curves have a bad radial investigation depth, with a good vertical resolution; phase shift curves can distinguish the thin sand-shale interbeded formation. As a result, it supports a lot on processing and inversion of logging data. 3. With the Electromagnetic Propagated Resistivity Logging with several mega-hertz operation frequency widely used, by a representative formation model, the effect of operation frequency and spacing on logging responses is investigated systematically. These results are useful on designing of logging tools.