Research on Downhole Electromagnetic Repeater Transmission Characteristics in Ultra High Resistivity Gypsum-Salt Layers

In order to solve the problem that electromagnetic telemetry signal easily interrupts transmission in ultra high resistivity gypsum-salt layer due to fast attenuation,an adaptive HP finite element method (FEM),which could automatically select space or order thinning,was used to simulate the electromagnetic relay in ultra high resistivity gypsum-salt layers.The falling velocity and transmission distance of electromagnetic signals in ultra-high resistivity gypsum-salt layer under different carrier frequencies were obtained.A prediction method of relay installation position was formed,and compared with conventional finite element calculation.It had advantages in convergence rate and calculation accuracy.The the algorithm was verified correct in Well AJ214 of AGHA JARI Block,Iran.The calculation result of signal attenuation rate tallied well with the practical application,and the prediction accuracy of repeaters’ installation position was over 90%.The research showed that the transmission model could accurately predict the installation position of repeaters,and ensure the continuous transmission of electromagnetic signals across the ultra high resistivity gypsum-salt layer.The model can serve as a theoretical reference and foundation for EM-MWD applications.