Finite Element Simulation Analysis of Acoustic Transmission Characteristics for Periodic Pipe String Channels

Abstract

In the process of oil drilling, the acquisition and real-time transmission of downhole information is very important for the accurate evaluation of formation, reservoir description and development. The downhole acoustic transmission method is one of the important method of downhole information transmission. It uses the inherent pipe string channel in the well as the carrier of information transmission, and has the advantages of high transmission rate and good adaptability. Based on the finite element method (FEM), this paper firstly builds a two-dimensional axisymmetric pipe string model with the COMSOL software. An analysis about the acoustic transmission characteristics (time and frequency domain) of the periodic pipe string channel are then made. The effects of sudden change of acoustic impedance at the junction of casing and collar, viscous damping loss of drilling fluid and structural damping loss of pipe on acoustic transmission characteristics are studied. During the process, the spectral structure of the comb filter with alternating pass and stop bands is determined using the FEM. For the drilling fluid, it can be found that its viscous coupling with the pipe string would reduce the energy of the acoustic signal, whose amplitude attenuation in the pass band would become stronger as the frequency increases. Besides, the damping of pipe string channel structure would also reduce the energy in the passband as the traveling distance increases. Finally, the evaluation experiment of the acoustic transmission characteristic of the pipe string channels is carried out, which demonstrated the correctness of the simulation results. These research results would further lay a foundation for the design and development of the acoustic remote transmission system.

Keywords

• pipe string channel
• channel modeling
• finite element method
• drilling fluid viscous damping
• structural damping