Study On Shallow Goaf Microseismic Location Methods

Underground goaf has a very serious harm to coal production and surface operation. Nowdays, geophysic shallow coal mining goaf exploration method mainly includes shallow earthquake method, radar method and CSAMT. Based on the feature that borehole-to-surface CT method motivates in the borehole and when it go across goal, it will scattering, we can recard scattering point as secondary source, and study it’s waveshape feature, then combined with initial velocity model of crosswell first-break traveltime tomography and microseismic soure location theory, we can lacate goaf.To address the issues described above, this dissertation carried out in-depth studies as following:(1) learn the geology feature of goaf and study the seiscmic data of goaf, analyze it’s average velocity, amplitude of firstbreak and frequency of firstbreak;(2) Analyze sacterred wave’s character, summarize an efficient method to indentify goaf scaterred wave. Use numerical modeling method to sthdy scattered wave’s feature on seismic record, verifying effectiveness of location method.(3) Base on the forward theory, classic Geiger location method and grid search method are analyzed to compare their advantages and disadvantages, and the rectangular segmentation inversion algorithm is put forward, which converges more fast and stably and avoids the problem of local convergence.(4) The influence rule of first break picking and velocity model on location results has been studied, and the seismic tomography theory is applied to the velocity model optimization.Based on the above research contents, this dissertation has made some important achievements as follows:(1)On account of the feature that sesmic wave will emerage scattering, we dudeced scattered wave’s feature of one point underground, and use this feature to find scattered wave from seismic data accurately.(2)As the shortcomings of conventional inversion algorithm, such as local convergence, initial value depence and slow operation speed, the rectangular segmentation inversion algorithm is introduced, which is global optimization based on variable grid ideas;(3)As for CT seismic record, the first arrival tomography theory is used to correct the velocity model, and the corrected velocity model is accurate.Finally, the research results above are used to process the borehole-to-surface CT data of a certain area. The feature of scattered wave generated by goaf underground is used to pick up the firstbreak time, and combining velocity model been corrected with classic Geiger location method, goaf locatinon exploration task is been completed.