| Measurement/logging while drilling (M/LWD) is a kind of advanced logging technology which is used to realize the goal of real-time data acquisition and transmission in the process of bit drilling. Because the drilling fluid channel which is widely used in logging while drilling system is a kind of time-space-frequency change, long time delay, and very limited feedback deletion channel, current transmission strategies can not achieve efficient and reliable logging data transmission. So current transmission strategies are unable to meet the demand of logging data transmission which comes from new business.First of all, because of the harsh drilling fluid channel conditions, conventional logging data transmission strategies are unable to ensure the efficiency and reliability of data transmission at the same time. Second, with the development of the large amount of data imaging logging technology, to transmit a large number of well logging data to the ground control center in a timely and reliable way is an urgent problem. The existing transmission strategies cannot solve this problem. Third, the intelligent closed-loop control is the future development trend. But existing logging while drilling data transmission strategies don’t support variable code rate transmission, so cannot provides channel adaptive way of data transmission. Fourth, the existing source encoding for logging while drilling data is only suitable for a specific type of data. The limited applicability regulates logging while drilling in the transmission efficiency.This article has carried on comprehensive and thorough research for the above four key problems in logging data real-time transmission. Main innovation works are as follows:(1) We solve the effective data representation problem, measurement errors elimination problem and reconstruction matrix matching problem which are all caused by the compressive sensing on logging data transmission. Then we propose a conventional logging data transmission strategy based on the theory of the compressive sensing. The proposed strategy has the advantages of linear coding complexity, which implements information accumulation. It overcomes the shortcomings of traditional forward error correction coding and feedback retransmission technology, such as low channel transmission efficiency, a lot of feedback, and large amount of calculation. Experiments performed with real logging data show that our proposed strategy improves the coding efficiency and reduces the logging data loss compared with the existing transmission strategies. Besides, with our proposed strategy, the ground control center is allowed to adjust the sending rate according to the channel state for reliable data transmission in different channel conditions.(2) We puts forward a novle log data real-time transmission strategy on the basis of R10 codes for the M/LWD systems with large amount data to be delivered. We present an analysis framework to evaluate the information loss of the system by treated it as a integer splitting model under the condition of constraint. The proposed transmission strategy solves the logging data real-time transmission problem with the trend of increasing amount of logging data. Using the integer splitting theory and combinatorial mathematics, we analyse the transmission reliability and efficiency of the proposed strategy. Combining with the characteristics of logging while drilling, we also give the optimal parameters setting rules. The simulation results show that the proposed strategy improves the transmission efficiency and reduces the logging data loss. The biggest advantage of this strategy is in its good extensibility, so it is suitable for the future trend of increasing amount of logging data.(3) In view of the drilling technology development trend of intelligent closed-loop control, we put forward a kind of logging data real-time channel adaptive transmission strategy based on RaptorQ codes. The proposed strategy has the advantages of high efficiency, low complexity, low frequency feedback, small amount of feedback and feedback in advance. The ground control center tracks channel quality change in the process of drilling, and adaptively adjust underground transmission parameters to improve the log data transmission timeliness and reliability in the drilling process. This research work provides technical reference for fast stable log data transmission under the condition of closed loop communication.(4) By analyzing the information entropy, probability distributions and correlation coefficient of actual logging while drilling data, a logging data real-time compression coding method based on differential pulse code modulation algorithm is presented. This method has the advantages of constant order algorithm complexity, flexible adjustment of decoding quality, and wide applicability. Experimental results performed with real logging data show that the proposed method can compress the logging data to less than half of the amount of original data, under the premise of not interfering with the Engineers judge. |
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