Optimal Energy Transfer Pipe Arrangement for Acoustic Drill String Telemetry
Drill string acoustic telemetry is an effective transmission method to retrieve downhole data. Finite-difference simulations produce the comb-filter-like channel response (patterns of pass bands and stop bands) due to the presence of coupling joints in the metallic drill string. Practical pipes used for drilling deep wells have slight variation in length. The selection and arrangement of downhole pipes is important for improving the transmission efficiency of extensional waves transmitted through the drill string. Downhole drill string channel is studied using the transmission coefficients calculated from the transmission matrix method, and the resultant transfer function produces identical results similar to the finite-difference simulations. Reciprocity of the drill string structure is proved by comparing the pass band responses using the ascend-only (AO) and descend-only pipe arrangements. Transferred energies calculated up to 180 pipes of random length at the end of the drill strings using transmission coefficients for the three different pipe arrangements, namely, AO, descend-then-ascend, and ascend-then-descend (ATD), are compared to find the optimal pipe arrangement for single measurement. For the situations when pipes are distributed in sets, multiple measurements are required. In this paper, two sets of AO and two sets of ATD arrangements are analyzed for multiple measurements. ATD and nxATD arrangements are proposed as optimal pipe arrangements to produce the best possible telemetry performance in terms of optimal acoustic energy transfer via one- and two-way acoustic communication for single and multiple measurements, respectively.
Design of acoustic transmission along drill strings for logging while drilling data based on adaptive NC-OFDM
Abstract This paper represents a new scheme using the drill strings as the medium to deliver logging information via a compressional acoustic wave. Considering the comb-type frequency characteristics of an acoustic channel, non-contiguous orthogonal frequency division multiplexing (NC-OFDM) has been selected as a promising technique for achieving high-rate transmission with high spectral efficiency and immunity to multipath channels. However, the irregular pilot design and high peak-to-average power ratio (PAPR) halted the widespread application of NC-OFDM. To overcome these two disadvantages, we propose an adaptive pilot design scheme in which the dynamic range of available frequency is pre-simulated and an improved discrete Fourier transformation based least square (PDFT-LS) channel estimation scheme to obtain the channel characteristics and an improved selected mapping (PSLM) scheme with low-complexity to reduce the PAPR of the transmitter are applied. Computer simulation and circuit test results are presented to demonstrate that the data transmission rate can be in excess of 500 bps along a 53.76 m experimental channel under the conditions of the simulated impulse noise and surface noise with a low bit error rate (BER), and the PAPR reduction performance can reach almost the same as that of a conventional SLM (CSLM) scheme.
Proposed beam diagnostics instrumentation for the LANSCE refurbishment project
Presently, the Los Alamos National Laboratory is in the process of planning a refurbishment of various subsystems within its Los Alamos Neutron Science Center accelerator facility. A part of this LANSCE facility refurbishment will include some replacement of and improvement to existing older beam-diagnostics instrumentation. While plans are still being discussed, some instrumentation that is under improvement or replacement consideration are beam phase and position measurements within the 805-MHz side-coupled cavity linac, slow wire profile measurements, typically known as wire scanners, and possibly additional installation of fast ionization-chamber loss monitors. This paper will briefly describe the requirements for these beam measurements, what we have done thus far to answer these requirements, and some of the technical issues related to the implementation of the instrumentation.