Modeling And Application Of EM-MWD Signal Transmission

With the rapid development of the world economy,the demand for oil is also growing,the drilling technology research is particularly important.The key technology of the logging is the transmission of the drilling signal.At present,the electromagnetic wave transmission is attracting more and more attention.The electromagnetic wave transmission is simple to operate and implement.The transmission rate is high and is not limited by the mud.It can be applied to air,foam or mud underbalanced drilling.In this paper,finite element analysis(FEM)is used to model the MWD signal transmission.Based on the Maxwell equations,the functional equations of the electric field vector in the stratigraphic medium and the truncated boundary condition are used to express the functional expression.Based on the hexagonal partition under the cylindrical coordinate system,it is better to fit the drilling model.Using of the high-order laminated vector basis function,we can control the order of the basis function freely.In the model meticulous or source area increasing the mesh,using high-order basis function,while in the far range,the mesh is reduced and the lower order basis function is used.It’s not only can improve the calculation precision,but also speed up the calculation rate.Finally,the required reception voltage is obtained by the expansion of the global electric field.The finite element method is used to simulate the electromagnetic transmission in different situations,and the optimal length of the insulation section is 1m when the insulation gap is used.The excitation structure,the relay and the ground receiving antenna,the relay receiving distance and the frequency are optimized.Comparison of the influence of water-based mud and oil-based mud on the electromagnetic transmission.Find the optimal location of the ground receiving antenna for the sloping formation and analyze the effect of the stratified formation on the sloping formation.Analyze the effect of metal bushings,drill pipe sticks on metal bushings and blowout preventer for EM-MWD,Which laid the foundation for the further study of electromagnetic energy transmission.Finally,the maritime logging signal transmission system is introduced.It ues wired transmission and wireless transmission combined with the way.Communication cables are used to transmit the signal in the sea where the electromagnetic wave attenuation seriously,while the electromagnetic wave is used in the submarine strata.And compare two different receiving antennas.The results show that using the spiral coil is better than the linear antenna.