| The demand for data transmission speed of logging equipment in oil exploration and digital acquisition technology field is higher and higher.In the research of borehole high-speed data transmission system,it is the prerequisite to analyze the transmission characteristics of the transmission medium and design communication schemes for implementing the function of the system.It is also a time-consuming and money-consuming test work to obtain a variety of cable's transmission characteristics with different specifications in the early stage of instrument design,because the 1000-meter seven-core armored logging cable weighs in tons.Therefore,it is necessary to study the modeling simulation method to obtain seven-core armored logging cable's transmission characteristics of any length.First,this paper has explained that the 1000-meter seven-core armored logging cable needs to be treated as a distributed parameter circuit element in the frequency band(k Hz or higher)that may be used in this article.The large number of distribution parameters not only represent the complex changes in the transmission of electromagnetic waves in the seven-core armored logging cable,but also is the main factor that makes it difficult to express the transmission characteristics by a specific formula.With simplifying the change of the electromagnetic field on the cable,the multiconductor transmission line model of the seven-core armored logging cable is established under the premise that the seven-core armored logging cable belongs to the quasi-transverse electromagnetic field.The simulation study on the transmission characteristics of the seven-core armored logging cable is divided into two steps: calculating the distribution parameters and solving the transmission line equation.Then,this paper has used the finite element analysis method to calculate the unit length distribution parameters of cable.Which shows that the unit length distribution resistance and the unit length distribution inductance vary with frequency,which is the main factor to characterize the cable's transmission characteristic.Finally,the frequency domain analysis method which can easily handle the frequency change parameters is used to solve the multiconductor transmission line equation,and get the cable core's voltage and current value,then get the transmission characteristics of seven-core armored logging cable.The transmission characteristics of a seven-core armored logging cable's external and intermediate core which is 3km long are simulated,and the results are compared with the measured results.It is shown that the calculated results reflect the change of the measurement results well and the average relative error is 10%.Then the method of improving the precision is put forward by analyzing the causes of the error.This paper has also used the simulation data of a 3km cable's intermediate and external core to produce the solid simulation model and test,of which the results show that the simulation model can show the change of cable output signal varies with time accurately,except for the amplitude difference caused by the simulation calculation error. |
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