Evaluation of coal seam roof water-bearing risk area via anisotropic high-resolution seismic processing

Abstract

With the increasing importance of mine water prevention and control in coal mining, higher requirements have been put forward for precise seismic exploration methods. Conventional seismic exploration based on isotropy is increasingly unable to meet the high-precision exploration requirements for coal seams and their roof and floor under complex conditions. Based on the orthogonal anisotropy characteristics of coal bearing strata, the periodic thin interlayer anisotropy and fracture induced anisotropy are comprehensively considered. A wide-angle imaging method based on high-order motion correction is proposed to flatten the in-phase axis and improve the accuracy of far and near offset motion correction for the characteristics of the transverse isoropy medium with vertical symmetry axis(VTI). Applying the Offset Vector Tile(OVT) domain processing to eliminate anisotropy in different directions under structural fractures in coal bearing strata, in response to the characteristics of the transverse isoropy with horizontal axis ofs symmetry medium(HTI). Improve imaging accuracy and resolution during seismic data processing. Improve imaging accuracy and resolution during the seismic data processing phase. On the basis of wide azimuth and high fidelity imaging, lithology interpretation is based on the pseudo acoustic method of rock physical characteristics. By reconstructing the acoustic time difference logging curve and incorporating formation lithology information into the velocity curve, the spatial distribution characteristics of formation lithology can be analyzed through inversion iteration. Fracture interpretation is based on ellipse fitting of azimuth offset information contained in OVT gathers to obtain attenuation gradient of seismic wave in different azimuth, and fracture density and azimuth are fitted to obtain distribution characteristics of formation fracture density. To achieve precise exploration of the two key parameters affecting mine flooding, the coal seam roof aquifer and the water conducting fracture zone. On this basis, a comprehensive evaluation is conducted on the water production risk zone of the coal seam roof. The actual water content risk assessment of the data is in good agreement with the production well situation. The method was applied to the research area, and the actual data of water content risk assessment matched well with the production well situation. The results verified the feasibility and applicability of the proposed risk assessment method, providing useful reference for predicting mine flood risk areas in coal mining.

Keywords

• orthotropic medium
• ovt processing
• roof and floor rock
• fissure system
• water content evaluation