MWD Mud Pulse Signal Identification And Ground Adaptation Technology Research

Presently, in the process of drilling the oil-wells, wireless MWD (measurementwhile drilling) technology has been widely used with purposes of measuring theborehole parameters accurately, improving the control to well trajectory, and guidingthe drill head to the target oil layer precisely. Wireless MWD is an abbreviation forthe measurement and transmission of the real-time underground information duringthe drilling process, with such characteristics: to obtain geological information nearthe drill head without interrupting its normal drilling process, and turn the informationinto wireless signals to transmit them up to the ground; next, these signals will beanalyzed and treated within ground system, by which the signals can be decoded in anencoding way that matches the underground apparatus, to get the orientation data,stratum features, drilling parameters and other information that are required in drillingprocess.The objective of this thesis is to improve the transmission speed and decodingaccuracy of MWD mud pulse signals. Signal transmission in drill string will beaffected by various site conditions. Consequently, pressure wave of mud pulse signal,detected by pressure sensor which is placed at the mouth of the well, contains a greatnumber of noise signals, which are generated due largely to the rotations or vibrationsof the underground machines. Such noise signals would dominate the original pulsesignals. Even that the mud pulse signals have not been disturbed by noises, theywould be attenuated sharply after a long way of transmission, or, due to the quality ofmud itself. Therefore, for the technology of transmitting the mud pulse signals, it is aprimary problem to detect the weak mud pulse signals out of those strong noiseswhich have unfixed frequencies. This paper was arranged with following mainchapters and content, as:Chapter I, introduction. This part summarized the importance of wireless MWDground system for oil-well drilling, analyzed and compared the working principlesand performances of many types of wireless transmission technologies, introducedlatest developments of China’s as well as foreign literatures which made researcheson the wireless MWD that takes the mud pulse signals as its transmission media, andpresented methods of extracting and identifying mud pulse signals with highresolution, for the accurate extraction and identification of mud pulse signals. In chapter II, characteristics of mud pulse signal transmission were analyzed;factors, which have impacts on the sticky speed of mud pulse signals as well as on thetransmission speed of drilling liquid under ideal conditions, were studied; attenuationand its influencing factors of the mud pulse signals when they run through the drillstring were researched, and a mathematical simulation model to attenuation’sinfluencing factors was built, to provide basis for the design of ground signals’hardware circuit.In chapter III, the Manchester Encoding and PLM Encoding for undergrounddata were described, Transmittal formats of these two encoding methods and theprovisions to special signals in transmission were taken into consideration, to offer atheoretical basis for wireless MWD data’s encoding mode and decoding order.In chapter IV, treatment to noises that mixed in mud pulse signals was studied.The mud pulse signals are disturbed by various noises, so, this part firstly researchedthe spectral characteristics of original mud pulse signals, figured out differentcharacteristics between noises and useful signals, analyzed the types of noise signals,and set up a relatively complete denoising algorithm and process which caneffectively extract the mud pulse signals, to lay a foundation for next accurateidentification.In chapter V, a model for identifying mud pulse signals was established topropose the theoretical basis of recognition algorithm for mud pulse signals. For thoseencoded by Manchester, the recognition algorithm ban be conducted within single-bitperiod, such as local feature recognition algorithm, phase recognition algorithm,correlation recognition algorithm, and within multi-bits period, such as clusteringrecognition algorithm, fuzzy clustering recognition algorithm; for those encoded byPLM, the rising edge feature recognition algorithm and waveform similarity featurerecognition algorithm were presented.In chapter VI, ground signal collection box and decoding software were designed.Based on knowing the transmission characteristics of mud pulse signals, this partdesigned for ground signals a set of preprocessing circuit and hardware filter circuit,by which the signals can be initially preprocessed and the signals of differentfrequencies can be filtered to eliminate the disturbance on useful signals. The grounddecoding software which was developed by using VC++6.0, includes a USB interfacewas employed to collect data. In the process of designing the software, differentdigital filters and relevant parameters were chosen in real time according to different needs. In the identification of mud pulse signals, the real time data were decoded bythose identification algorithms, realizing the multi-thread dynamic data storage. Thesoftware has friendly interface with good maneuverability. Finally, the experimentalresults showed that the ground system can reach the expected functions and thedesigned objectives had been achieved basically.The last part of this thesis is about the conclusions and prospects in futureresearches.