Discussion on Commonly Methods for Analysis of Drill String Acoustic Spectral Characteristics

Abstract

Finite difference method and transfer matrix method were used to get spectrum response curve of unit impulse function signal to research the spectrum characteristics of acoustic traveling though the drill string. Similarities and differences of the two methods were discussed through analysis of spectrum curve get from the two approaches. The results show that: The distribution of band-pass and band-stop get by the two calculating methods is basically the same, some transmission coefficient of finite difference method is less than 1, is not completely transmission phenomenon. Analysis of the reason for this is that the transfer matrix method is an analytic method, finite difference method is a numerical algorithm. From the calculation precision of speaking, analytic algorithm is higher than that of numerical algorithm. But to verify the reliability of two methods needs based on laboratory experiment or field test.

Optimal Energy Transfer Pipe Arrangement for Acoustic Drill String Telemetry

“…4, both methods have provided the combfilter response and match well with each other. However, the spectrum obtained from the transmission matrix method is smooth and gives maximum gain (complete transmission) [20], as shown in Fig. 4 (subplot 2), at the peaks at around 935.5 and 946.5 Hz.…”

“…If these variable pipe lengths are assembled for a drill string, the energy in the pass bands, particularly higher pass bands, is totally lost. To study the frequency responses of the variable length long drill strings, the transmission matrix method, which gives more precise and accurate results [20], [21], is included next.…”

“…FDTD's frequency resolution is limited to the sampling time, compared with the transmission matrix method. Moreover, the transmission matrix method is simple and produces more precise response [20], [21]. Therefore, it is used for further analysis to find the optimal pipe arrangement using more pipes; random pipe lengths with mean, i.e., μ, of 9.45 m and standard deviation, i.e., σ, of 0.16 m are considered to match with practical drill pipe lengths [15], [24]; tool joint length is fixed as 0.5 m.…”