Abstract
The casing string is a very good down-hole signal transmission channel due to its rigidity which means it can reduce attenuation in vibration wave propagation. Based on elastic mechanics theory, we obtain the wave equations of vibration propagating in the free casing, analyze the transmitting law of the vibration wave in the well fluid-casing-cement system and found that the attenuation of the vibration wave is mainly caused by the energy absorbed including the well fluid, the casing and the cement ring. Based on the attenuation factors which affect the wave propagation, we get the vibration wave attenuation coefficient model and calculate the relative attenuation coefficients in different casing strings. By detecting and analyzing the drilling plug signal in the second spud, the field test results prove the feasibility of long-distance transmission and the low attenuation of vibration wave in the casing string, and get the attenuation coefficient of casing size 9 5/8, which is similar to the simulation result.
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