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.
Downhole pipe selection and arrangement for acoustic drillstring telemetry
Drillstring acoustic telemetry is an effective transmission method to retrieve downhole data. In this paper, finite-difference algorithm is used for acoustic wave propagation prediction along the drillstring. An impulse excitation signal of time duration 30.87 μs is transmitted from the downhole and the wave displacement at the receiver is found using finite-difference algorithm. The resultant impulse and frequency responses are plotted and compared for different segments. It is found that the selection and arrangement of downhole pipes plays a vital role in improving the transmission efficiency of extensional waves transmitted through the drillstring for acoustic telemetry, particularly in the high-frequency bands. In order to find the optimal pipe arrangement order, 4 segments of drillstring with lengths d11to d14 (in increasing length between 9.3434 m and 9.8185 m) are arranged in all 24possible permutations. The energy of the frequency response is found for each of the six pass bands for the twenty four arrangements. It is concluded from the findings that placing the shortest pipe at the downhole first, followed by the longest pipe, then the next longest pipe and so on, produces the best possible telemetry performance in terms of optimal acoustic energy transfer.
Finite Difference Modeling on the Temperature Field of Substrate in Friction Surfacing
Friction surfacing is an advanced process of great potential, especially in the field of repair and reclamation of worn and damaged components. As a kind of thermal processing technology, the temperature profile and changes of the substrate in friction surfacing are important factors to get coatings of high quality. In this paper, the temperature field of the substrate during the process is simulated by finite difference method. The results are consistent with experiments, reappearing the temperature change of the substrate during friction surfacing, allowing further study on figuration and quality of coatings.