Research And Application On High Gas Mine Oriented 3D Seismic Technology

China has a mass of high gas coal mines and there are various main control factors that determine the gas enrichment area and the distribution of highly coal and gas outburst zone. Therefore, it is important to study on the application of 3D seismic prospecting technology to the predication of gas enrichment degree based on specific main control factors.At present, there are many problems in applying 3D seismic prospecting technology to the exploration of high gas coal mines, such as lack of means in acquisition, processing and interpretation work, lack of a clear objective and poor skill level on the part of new technology application. Aiming at the above mentioned problems and based on a research project sponsored by Yang Quan Coal Industry( Group ) Co.,LTD, namely"the Study and Application of Seismic Inversion Technology to Gas Enrichment Area Prediction", the paper made a systematic study on the topic. It analyzed the main control factors (flexural structure) affecting the distribution of high gas enrichment area in the coal mine in question and adopted a 3D forward modeling method to figure out the appropriate 3D seismic observation pattern for the specific condition of the area; Through a contrastive analysis on the results of time-domain pre-stack versus post-stack migratation, the necessity and advantage about pre-stack migratation is cleared; employing the new technology of pre-stack Elastic impendence inversion and Spectral Decomposition, the paper also predicted the gas enrichment degree of the target coal seam as well as the distribution of highly dangerous zone. The following are the main conclusions:1. Based on analysis of many geologic factors, such as structure evolution history and development characteristics, coal seam formation depositional environment, and the distribution features such as coal thickness, rank, coal body, gas bearing, it is concluded in the paper that the flexural structure is the main control factor affecting the distribution of gas enrichment area, coal and gas outburst region in Shigang Coal Mine.2. Establishing the 3D model of complex undulating surface and underground flexural structures by ray tracing of 3D constant velocity gradient, it conducted forward modeling to study variation characteristics of several CRP bin attributes about the high frequency energy resulting from the wide and thin observation azimuthal systems with different observation direction. The necessity of adopting the wide-azimuthral observation method is pointed out in the paper.3. Comparing the actual processing results and the interpretation results from pre-stack and post-stack migratation respectively, it is proved in the paper that pre-stack migratation is more effective in qualitative and quantitative interpretation of complex structure as well as improving the recognition rate of small structure of collapse column.4. Using post-stack multi-well constrained inversion method, the thickness variation tendency of the No.15 coal seam was predicted. It is proposed for the first time to use the maximum positive and negative curvature attributes to analyze the planar distribution and deformation features of flexural zone. Combined with the predicted result of the tectonized coal body achieved through the resistivity pseudo-acoustic characteristic parameters inversion method, it is concluded in the paper that the distribution range of tectonized coal body is determined by the flexural structure.5. For the first time the 3D seismic prestack elastic impendence inversion (EI) technology is applied to predicting the gas enrichment range in high gas mine. Vp/Vs ratio shows clear negative linear correlation with gas bearing. In general, the predicted results is consistent with the measured gas bearing values and fits in with the gas enrichment ranges in high gas emission zone. Considering the lack of acoustic logging data, it is a good attempt to base the EI inversion method in this study on two angle-stack data.6. It is the first attempt to apply spectral decomposition technology with wavelet transform algorithm to study the coal and gas outburst region. The study not only found the relative high attenuation response feature about high frequency reflection energy in gas outburst coal body, it also completed a semi-quantitative analysis and determined the distribution of coal and gas outburst region. Since the predicted results on the whole accord with the gas geologic law, it may offer some useful guidance to underground mining work.