A Method of Surface Electromagnetic Wave Transmission Across Discontinuous Structures in Wellbore Environment

Downhole signal wireless transmission based on surface electromagnetic wave is an important research field of modern fast drilling and production well intelligence. In the channel of the surface electromagnetic wave transmission based on the metal pipe and surrounding medium in borehole, the discontinuity caused by the collar of the metal pipe leads to the change of the boundary conditions for surface electromagnetic wave transmission, resulting in a mismatch of electromagnetic momentum and change in transmission mode from the surface wave mode to the radiation wave mode. This in turn causes severe attenuation of signal strength, which seriously affects the transmission distance of surface electromagnetic waves. For this, a low-attenuation obstacle-crossing device based on a multi-layer composite medium structure is proposed, which converts the radiation of electromagnetic waves excited by the discontinuous structure into surface electromagnetic wave transmission, thereby reducing the degree of signal attenuation. Through simulation and emulation of the structure via electric field integral equation based on the algorithm of adaptive cross approximation inverse, experimental results show that the device can effectively reduce the degree of signal attenuation when surface electromagnetic waves pass through obstacles, thereby improving communication reliability. The signal improvement can reach about 10 dB in the frequency band of 5 MHz to 2.4 GHz in our experimental tests.