Continuous Pressure Fluctuation Propagation In Pipeline And Its Application In Measurement-while-drilling And Hanger Pressure Test

Continuous fluctuation of pressure generally appears in pipes, which can sometimes be useful, and sometimes harmful. During MWD, the measurement information under the shaft is transmitted to the ground through the pressure fluctuation of drilling fluid inside the drilling stem, which can improve the accuracy of the drilling operation and reduce the cost of operation. However, in the process of transferring data, there often exists a problem that sometimes there are signals, sometimes there is no signal. Therefore, we need to find the law of the signal transmission in drilling fluid in order to ensure the stability and reliability of data transmission. The rapid increase of pressure in the process of hanger pressure measurement accompanied by severe fluctuations causes a very big deviation of the action pressure of the hanger. Facing the problem of how to reduce the pressure fluctuation in the pipeline and improve the accuracy of measurement,whether the fluctuation of pressure is utilized or controlled, it need to intensively research the transmitting law and characteristics of the fluctuation in order to explore the essence and influence factor of the problem.Based on the theory of pulse wave, the matrix transfer model of continuous pressure wave in pipes is established, and the law of continuous wave in the pipes is thoroughly study by transfer function in this paper. The model not only can explain the transmission of the continuous wave in drill string and solve the problem of selecting the carrier frequency of MWD, but also can be used to analyze the transmission of the continuous wave in the test pressure pipeline, The filter pipeline structure is designed, which provides theoretical basis for solving the problem of poor measurement accuracy of pressure measurement in the process of hanger pressure test. This paper mainly studies the following aspects:Firstly, as to the attenuation of continuous wave in pipes, which can not be accurately analyzed by means of the traditional fluctuation theory, the fluctuation model based on bidirectional coefficient of transmission is established by studying the transferring phenomenon of continuous waves. By way of this new model, the relations between the fluctuation transfer, the pipes’ dimensions, resistance and the characteristics of fluid can be accurately represented. The real part of the coefficient represents the propagation of wave amplitude due to the pipes and the imaginary part represents the influence of the pipes on the wave phase. To sharp-inclined pipes, the real part of the two coefficients is different, which shows that the fluctuation transfer along the direction of gravity and that against the direction of gravity is of some difference. The relations between long pipes and the transfer of continuous fluctuation is similar to the relation between the voltage and current in transmission line, so the formula of the impedance in pipes and the characteristic impedance can be defined and the continuous fluctuation in pipes can be analyzed through the analytic method for power transmission line.Secondly, with respect to solving the problem that it is difficult to choose the carrier frequency during MWD, after studying the fluctuation of pressure and the flow rate of the two ends of pipes, the transfer matrix model and transfer function that represent the transfer of pipe fluctuation is established. By means of analyzing the model, the distribution of the pressure fluctuation in pipes is obtained, that is during continuous fluctuation, the pressure fluctuation appears in standing wave. By analyzing the transfer function, the amplitude frequency characteristic of pipes is obtained which shows the pipes’ attenuation is different towards different frequency, the attenuation appears during the whole transfer, low frequency is in accordance with the low attenuation and high frequency is in accordance with the high attenuation, and the pipe serves as low pass filter for high-frequency fluctuation, which provides the reasons why the signal in the pit is sometimes strong and sometimes weak during MWD. Based on the mentioned research results, the dynamic choosing method for the carrier frequency in MWD is proposed, and the experiment of pipe amplitude frequency shows that pipes have an impact on the fluctuation transfer of different frequency.Thirdly, regarding the problem that the fluctuation transfer in pipes of different structure can not be effectively analyzed by way of the traditional method, improve the matrix analysis model for the fluctuation transfer in pipes based on the transfer model of continuous fluctuation in pipes in order to analyze the influence of different pipes on the continuous fluctuation. Since most parts of the above ground pipes are horizontal or small-angled, the simplified model can be applicable to the transfer model of wave in the above ground horizontal pipe. For the pipe networks with complex structure, the influence function is established to show the influence of branch pipes and the container on the main pipes, from which the calculation method of the transfer of continuous fluctuations is obtained. The author designs pipe construction with container and carries out amplitude frequency experiments, the experiments shows that the result of the propagation of the fluctuation with different frequencies is the same as the calculating result by the model.Finally, according to the dramatic pressure fluctuation in the process of hanger pressure measurement, the conclusion is drawn that the fluctuation can be restrained by the pipe structure. The pipeline structure, which is used to suppress the fluctuation of pump pressure in the process of test pressure of hanger, is designed based on the wave suppression characteristic, and the pressure test is conducted. The experiment result shows the conclusion is correct, which solves the problem that the dramatic fluctuation leading to big test deviation in pressure test.