A new reliability optimization and predictive control algorithm for simulation of azimuthal electromagnetic wave LWD tool

It is difficult to collect the whole life-cycle degradation data of the azimuthal electromagnetic wave logging-while-drilling (LWD) tool because of the long degradation period of the antenna system. Thus, it is hard to accurately evaluate the reliability of the tool when it is in the process of geological guidance. Meanwhile, aiming to the problem of difficulty to accurately predicting the reliability of the tool under the condition of small sample reliability data, the reliability optimization modeling method to the tool’s antenna system based on Weibull failure distribution has been proposed. At first, by means of environmental stress reliability test the failure mode and the failure time of the antenna system can be fitted and counted. Then, the reliability failure distribution model of the antenna system can be built up. Secondly, different combination models of antenna system which contain different arrangement and combination model of key components and other components have been built up. And by using these models, the impact of the overall reliability of the tool can be calculated and analyzed when it under the condition of different arrangement and combination of the key components and others. After that, the optimal combination cascade model of the key components and others can be obtained. The last, by using reliability performance indicators and combined with the optimal combination cascade model of antenna system, the overall reliability of the tool can be computed. And the remaining service life (RSL) of the antenna system also can be predicted. Research results show that the combination and cascading of the key components and others in the antenna system can change the overall reliability of the antenna system. When the tool continuous working to 200 h, Model A cascade model shows the maximize overall reliability to the antenna system. And by using this model the RSAB1 can achieve to 0.79. By adopting the reliability optimization allocation method which proposed in this paper, the overall reliability of the antenna system can be effectively improved and the RSAB1 can reach to 0.85. When the RSAB1 drops to 0.80, the antenna sleeve has the biggest TRSL which is equal to 158.46 h. And the turbine generator has the lowest TRSL which is equal to 27.1 h. Meanwhile, by calculating the mean absolute percentage error (MAPE) between the real lifespan and predicted lifespan of each part, it shows that the maximum MAPE value is equal to 8.5% and the minimum value is equal to 4.7%. Therefore, the RSL prediction model of the antenna system proposed in this paper can effectively evaluate the reliability of the antenna system of the tool when it is in the failure state. And it can provide effective technical support for the reliability prediction and evaluation of the azimuthal electromagnetic wave LWD tool.