Research On Key Technology Of The Digital High-density 3D Seismic Exploration In Coal Mine

The accuracy of conventional 3D seismic exploration in coal mine is becoming difficult to meet the requirement of coal mine’s safe and efficient mining. Digital high-density 3D seismic exploration technology has been applied in petroleum and natural gas exploration successfully. Can this technology be used to coal mine? We need to carry out some theoretical analysis and method research to validate that this technology can achieve the goal of fine seismic exploration in coal mine or not.First, we designed the typical geological model which simulated high-density sampling technology by 2D and 3D forward modeling software. The simulation result shows the intrinsic relationship between sample interval and seismic resolution, and we analyzed this relationship qualitatively and quantitatively. Secondly, we compared the difference between digital geophone and analog geophone in mechanical structure, working principle and performance parameters by laboratory test and field data analysis. Then, according to the characteristics of single point high-density seismic data, we focused on the study of the methods of indoor combination, denoising, weak signal recognition and improving resolution. The effectiveness of the above methods is verified by theoretical and practical data. Finally, we compared the application effect of digital high-density 3D seismic exploration with conventional 3D seismic in a Coal Mine.The main results are as follows:1) The relationship between seismic sampling interval and seismic vertical and lateral resolution is revealed in this paper. Horizontal resolution is based on continuous sampling of spatial wave field. Therefore, the smaller the space sampling interval, the higher the horizontal resolution limit reached; the vertical resolution in theory is based on the zero offset, but the vertical resolution in stacked section and migrated section actually is the integral of resolution in single channel with different offsets. The expression of vertical resolution has concave function property. This property determines that higher vertical resolution will always be reached by small spatial sampling interval.2) Digital detector has many advantage in theory, but it is not the case in actual test results. The laboratory test found that the deviation existed in amplitude frequency response and theoretical response for digital geophone. Because of the high sensitivity of digital geophone, it can receive all kinds of noise and signal which cause low signal-to-noise ratio in digital seismic data. In addition, field data also show that the dynamic range of digital geophone is not up to expectations.3) We introduced and improved the vector median filtering method. Vector is estimated by gradient structure tensor, which avoids the damage to dipping and buckled event by conventional median filter. Finally, we removed random noise with high fidelity. The adaptability of the 3D conical filtering method in the cross-spread is extended, and the surface wave is well suppressed in the processing of the actual data.4) Adaptive threshold function in curvelet domain is presented in this paper. It can significantly enhance the identification of weak signal by suppressing background noise.The research of digital high-density 3D seismic exploration technology need to be strengthened in optimization of observation system design, complex structure imaging, full 3D interpretation method, and so on. These will prompt the application of digital high-density 3D seismic exploration technology in coal mining area.