| Pipeline transportation is a very efficient and convenient transportation way, which plays an important role in the development of the economic. In China, the pipeline transportation has covered the transport of the water supply, gas supply and the oil supply, which has already been a significantly important portion related to people’s daily life and economic construction. As a newly arisen and economic transport way, the pipeline transportation has obvious characteristics such as stability and continuity, large amount of transport, more easily quality assurance. In recent years, the pipeline transportation’s obvious features have obtained long-term development. In the meantime, there are also risks of pipeline’s leakage for pipeline transportation. Moreover, in our country we still have the problem in lack of supervision and maintenance in pipeline transportation, once the pipeline leakage occurs, will not only cause economic losses but also trigger major security issues. At present, in our country, the average city supply water pipeline leakage rate has already been more than 20%, which has made a huge waste of resources. Therefore, how to monitor the pipeline leakage has certainly been a significant issue in ensuring the transport safety. Currently, most of the localization methods of the pipeline leakage are still in a 2-D pattern period and with limitation of various conditions. The methods, which are with more accurately localization characteristic, have more requirements on fields and equipment. What’s more, the methods, which can be taken more flexible, are always with low accuracy in localization. So, it has the theoretical and practical significance to establish a 3-D localization method based on setting detectors at any point on the ground for monitoring the pipeline leakage.In this paper, based on the formation of microseisms in pipeline leak, and by studying the formation theory of the leakage point, the micro-seismic wave spreading principles as well as the wave features, the 3-D localization of the leakage point method could be established, which can supply theoretical basis for the pipeline leakage acoustic observation system and the leakage 3-D localization. Further, the localization accuracy of the leakage point based on the micro-seismic monitoring technique would be improved, and the leakage point 3-D localization can be finally realized on the base of ground measurements.1) Using the relatively developed numerical modeling method of the 3-D acoustic wave equation of homogeneous isotropic medium, the finite difference pattern with accuracy of the time derivative’s second order difference and spatial derivative’s 2N order difference, as well as its stability condition, are all shown. In this work, the 3-D high-order staggered-grid finite difference method of the acoustic wave equation is also studied, the boundary condition selections are discussed and the wave equation’s staggered-grid finite difference pattern transferring in 3-D isotropic materials in non-divided CPML boundary condition is deduced. Meanwhile, the continuous seismic source’s construction process is analyzed.2) Considering the city water supply pipeline leakage feature and the characteristic of the continuous micro-seismic source, the micro-seismic function’s construction and analysis are conducted. Using the Ricker Wavelet based on the actual signals main frequency as the mother wavelet and random numbers generated by random functions as the amplitude factor of a time wavelet, the continuous leakage point’s micro-seismic source are constructed and are consistent with the actual seismic source, as well as for the simulated records feature and the actual wave feature. This work supplies seismic source mathematical model for the 3D theoretical simulation, which is matched with the actual seismic source.3) Considering the city water supply pipeline leakage feature and the special geology structure, the underground leakage 3D geological and geophysical model construction study are carried out. The models include horizontal single flat pipe in the homogeneous infinite half space, model with horizontal physical layer presented under the pipeline and model with fluctuate physical layers are constructed, which supply basis for the following study.4) Based on the built leakage continuous micro-seismic source mathematical model, the typical leakage 3D geological and geophysical model, and the 3D high order staggered-grid finite difference method, the leakage points micro-seismic wave field features of 3D numerical modeling and analysis are conducted, and get 3D micro-seismic wave field been consistent with the actual seismic source, which supply 3D micro-seismic simulated data for the following study.5) Considering the leakage 3D micro-seismic simulated data, the obtaining of the reference path time difference cross correlation and the generalized correlation processing method are used. The calculated method and feature analysis are conducted; the main factors that influent the time difference acquisition and the 3-D localization accuracy are studied; the veracity and the efficiency are then described. The results show: ① The mathematical model and the theoretical simulation results show that, the approximate plane localization can be realized on the basis of the vertex of the phase axis of the cross spectrum of two or more unparalleled survey lines. The approximate plane localization can provide basis for the reference path selection and the search range of the 3D localization inversion. ② the theoretical model simulation presents that no matter whether the reference path is a shortcut or far away path, the related time difference obtained can all be similar with the theoretical value, and the acquisition of the related time difference can be more efficient using the x component than the z component. Therefore, using the x component record and the nearby leakage path as the reference path can be better for the related time difference acquisition, which can improve the acquisition accuracy.③ when the value of the related time window is set, it will not heavily affect the related time difference acquisition accuracy of the related reference path, which means that, the related time difference acquisition accuracy has no relation with the related time window. When there is noise in the records, the effect on the related time difference acquisition accuracy is not obvious, and when the time window length is larger than 1000ms, the related time difference is matched with the accuracy requirement, which demonstrate that the method related to the reference path has a good feature of anti-noise.6) Directing at the 3D simulated micro-seismic data, using the simulated annealing for 3D localization inversion method, the effect on the localization accuracy and the data acquisition quality and reliability from different arrangements and arrangement parameters are detail discussed and analyzed, which can offer theoretical basis for the optimization selection, and demonstrated the correctness and effectiveness of the simulated annealing for 3D localization inversion method and the time difference acquisition relative to the reference path. The results show:① Singlet unilateral or bilateral of the vertical piping arrangement only effective access to the x-coordinate of the leakage and the parallel piping arrangement can only get the y-coordinate effectively, and now the skew wire arrangement survey line group cannot get any coordinates. This means that no matter singlet unilateral or bilateral cannot realize the 3D localization of the leakage.② Double parallel and orthogonal survey lines arranged group can effectively access to the 3D coordinate of the leakage. Relatively the positioning accuracy measured in terms of parallel line group is to be higher, skew wire arrangement survey line group can get a more accurate of x, y coordinates and the localization ability is similar with the two above. But it cannot localize z effectively. Generally, it is better to use double parallel survey lines arranged group to get the 3D coordinates of the leakage points. And it has higher localization accuracy, and it also matched with the actual requirements.③ Under certain circumstances the arrangement length, x, y and z inversion positioning accuracy is substantially independent of the track number; Under certain circumstance of knowing the number of tracks, x, y and z inversion positioning accuracy is related to the arrangement length (i.e., track pitch), which shows the largest errors in the cross section. So appropriate selection of the location and the length of the arrangement is conducive to effectively determine the leakage location.④ In the condition with noise, parallel group and the orthogonal survey line group have better accuracy of localization, relatively, z coordinates has larger relative error than that of coordinates x, y; the skew wire arrangement survey line group can just get the coordinates x, y and the accuracy of localization is higher than the two above, but it cannot localize the z effectively, which is caused by the reflection and refraction interference generated due to pipeline beneath the interface. This also demonstrates that the simulated annealing for 3D localization inversion method and the time difference acquisition relative to the reference path is anti-noise.⑤ when the depth of the leakage is known, any of the double lines arrangement survey lines can correctly get the plan coordinates of the leakage points, relatively, the accuracy of y is higher than that of x, and the skew wire arrangement survey line group has the best accuracy of localization and the orthogonal survey line group has less, the parallel group has the least.7) In order to demonstrate the effectiveness and adaptability of the simulated annealing for 3D localization inversion method and the time difference acquisition relative to the reference path, the data acquisition of the known pipeline leakage points are conducted and the tests of the simulated annealing for 3D localization inversion method are made and analyzed. This shows the 3D theoretical simulation is fitting with the actual leakage point’s micro-seismic wave feature and the of the simulated annealing for 3D localization inversion method and the time difference acquisition relative to the reference path can be used in the practice. The leakage localization is matched with the actual one and faces the requirement. However, the z (the depth of the leakage point) still has some bias, and relatively the errors of z are higher than that of the x and y. When the depth of the leakage is known, the x and y have higher localization accuracy.8) The theoretical and field tests illustrate that, the leakage 3-D localization theory and technique based on the ground observations records, as well as the processing flow line are formed, which can effectively realize the leakage point 3-D localization and supply a new way for the water supply pipeline leakage 3-D localization.In this study, the main problems solved are including: ① constructed the leakage point seismic function and the geophysical model; ② according to the water supply leakage environment and the seismic source feature effectively realized the micro-seismic simulation in 3-D acoustic wave high order staggered-grid finite difference;③ constructed the effective signal extraction method appropriate for the leakage seismic source feature, and using the forward simulation results to analyze the continuous random seismic source signal features to find the leakage signal identification method during the micro-seismic monitoring; ④ Constructed the seismic source localization method of the water supply pipeline leakage point and the monitoring system, and using the related techniques to calculate the time difference of the model without noise, and then compare the influence difference from different observations.The creative points in this study include: ① based on the formation features of the actual leakage and the actual leakage records wave field characteristics analysis, using the Ricker Wavelet based on the actual signals main frequency as the mother wavelet and random numbers generated by random functions as the amplitude factor of a time wavelet, the continuous leakage point’s micro-seismic source are constructed and are consistent with the actual seismic source, as well as for the simulated records feature and the actual wave feature; ② On the basis of the built leakage continuous micro-seismic source, by using the 3-D acoustic wave high order finite difference numerical simulation, the micro-seismic numerical simulation of the city water supply pipelines are realized effectively, and the simulated results match well with the actual records; ③ By the wave field characteristic of theoretical analysis and numerical simulation, time difference relative to the reference, the leakage point 3D localization and noise system analysis, the observation system of 3-D localization based on ground leakage records is determined. It is concluded that any single survey lines cannot realize the leakage point 3-D localization effectively, it is necessary to use the double survey lines arrangement to realize the localization and this can be with high anti-noise ability, also can match the practical requirement; ④ The leakage 3-D localization theory and technique based on the ground observations records, as well as the processing flow line are formed, which can effectively realize the leakage point 3-D localization and supply a new way for the water supply pipeline leakage 3-D localization. |
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