Numerical Simulation Of Complex Resistivity Logging

Complex resistivity logging (CRL) is an application of complex resistivity (CR) method in the wells, which is based on dispersion property of rocks and minerals. It is a method to explorate ore beds or to find oil by observant the abnormal of different frequencies electromagnetic wave in wells. Through a number of applications, it is considered to be able to overcome the shortcoming in conventional resistivity logging, which is hard to evaluate the flooded reservoir and reservoir with low resistivity accurately, so it is a potential kind of well logging method. Chinese researchers have done much research on CRL, which has not related to foreign reports, the CRL machine producted by Xinjiang Petroleum company firstly, which was named the Capacitance Logging. Later, Shengli Oilfield Company and Daqing Oilfield Company had also developed a similar logging equipment, and named as CRL tool. At present, the statement "Complex resistivity logging," has been generally recognized.However, most research of complex resistivity logging are on the study of electrode instrument, and the development instrument remain on restructuring of dual laterolog and laterolog-3. The research of coil instrument, which was believed has more prospect, is little. Only Ke Shi-zheng who has done some kind of research of coil method in the laboratory. So targeted research is necessary to carry out.The numerical simulation of Complex resistivity logging, which of great significance for the development of CRL instrument. The numerical simulation of complex resistivity logging is so little, and most of it is about Schlumberger array and dual laterolog sonde. In order to make the influence of stratum in coil-type CRL more clearly, I use FDTD to simulate the CRL. Finite Difference Time Domain Method (FDTD), is a direct time-domain electromagnetic field numerical solution. This method directly make Maxwell's two curl equations discretization use central difference into a set of explicit equations of the electromagnetic field recurrence in space and time. As a numerical method for electromagnetic fields, in recent years it has been used more and more widely.In order to achieve numerical simulation of the coil-type complex resistivity logging, firstly analyze the principle of complex resistivity, and make the formation mechanism more clearly. Then push down the FDTD equation and two-dimensional TE mode FDTD equation. After that i studied the use of cylindrical coordinates FDTD stability condition, numerical dispersion conditions and excitation of the set methods. In addition, I derivation the dispersion boundary conditions on cylindrical coordinates, and the method to do with corner approach in the two-dimensional TE model , and verify its good in electromagnetic wave's absorption. Based on FDTD formula, I program procedure in VC++ 6.0 platform, realize the two-dimensional TE-mode FDTD method. This program achieve the following functions: two-dimensional simulation of the measured of TE mode, the resumption of the process of calculating the formation resistivity log response curve; two-dimensional TE mode amplitude and phase parameters and the relationship between stratigraphy; the log response impact of slice in TE mode two-dimensional.According to the results of programming it can be concluded that response of logging is very sensitive and change of logging curve is clear when use FDTD to make forward modeling of electromagnetic wave logging. On this basis, we can draw the following conclusions. (1), FDTD method in dispersion medium can be realized on the simulation of coil-type complex resistivity logging, and can achieve good results. (2), The amplitude and phase curves drawn by forward all show that it changes by the parameters of underground media as typical dispersion curve phenomenon. (3), In the high-frequency conditions, the shape of the phase difference curve is much better than the amplitude ratio curve, it reflects the true distribution of the formation parameters better, so analyses the impact of bed thickness primarily based on phase difference curve. When formation thickness is greater than or equal to the length of coil, logging response is obvious at the interface of the formation, it can distinguish the interface of the formation exactly; When formation thickness is less than the length of coil, there lacks obvious signs of logging response at the interface of formation so that it makes a certain impact on distinguishing formation; (4), The changes of wellbore diameter and permittivity of bore mud have a smaller impact on logging response of electromagnetic wave logging. When the frequency is low it do not need to correct the impact of wellbore. When the frequency is high, the decay of electromagnetic wave is big in the hole, the impact of wellbore increases, it need to correct the impact of wellbore. (5), The coil-type complex resistivity logging tool in the frequency range 104 ~ 107Hz can comprehensive reply to the electrical dispersion properties of rocks strata's electrical parameters.Through the numerical simulation of complex resistivity logging by FDTD method, it lays a good foundation for the future research of the logging response of complex resistivity logging in all cases.