浅埋煤层风氧化带噪声自相关法探测技术

    Detection technology for weathered and oxidized zones in shallow-buried coal seams using noise autocorrelation method

    • 摘要: 煤层风氧化带发育会对浅部煤层回采产生严重影响。针对浅部煤层风氧化带的经济、高效探测难题,以宁东矿区浅埋6煤风氧化带探测为例,分析了噪声自相关方法探测煤层风氧化带的可行性,提出了一种基于子台阵假设的噪声自相关风氧化带圈定方法。研究结果表明:通过子台阵内部互相关函数的叠加,能够明显压制被动源地震记录中的强面波干扰,增强目标层体波反射信号;被动源噪声信号重建的6煤反射波与研究区的地质构造、6煤风氧化带下界高度吻合,依据其波形变化可圈定煤层风氧化带范围;相较于低频段与高频段地震剖面,中频段(10~40 Hz)地震剖面中的风氧化带导致波形差异最大;研究区风氧化带下界位于1 240~1 260 m煤层等高线之间,东侧较浅、西侧较深,与研究区内2口钻孔的揭露情况一致;鸳鸯湖−冯记沟背斜对风氧化带发育有显著影响,背斜核部风氧化带边界在1 250 m等高线附近;相较于地质推断结果,实测风氧化带西侧略浅100 m,东侧略深30~50 m,距工区南侧边界的最小距离约160 m。基于子台阵假设的噪声自相关方法能够经济、高效地探测浅埋煤层的风氧化带,适合大范围推广应用。

       

      Abstract: The development of weathered and oxidized zones in coal seams seriously affects the mining of shallow coal seams. Aiming at the economical and efficient detection of weathered and oxidized zones in shallow coal seams, taking the detection of the weathered and oxidized zone of shallow-buried No. 6 coal in the Ningdong Mining Area as an example, this paper analyzes the feasibility of detecting coal seam weathered and oxidized zones by using the noise autocorrelation method, and proposes a delineation method for weathered and oxidized zones based on the subarray-assumed noise autocorrelation technique. The research results show that the superposition of cross-correlation functions within subarrays can significantly suppress strong surface wave interference in passive seismic records and enhance the body wave reflection signals of target strata. The reflected waves of No.6 coal reconstructed from passive noise signals are highly consistent with the geological structures and the lower boundary of the weathered and oxidized zone of No.6 coal in the study area, and the scope of the weathered and oxidized zone can be delineated according to waveform variations. Compared with seismic profiles in low-frequency and high-frequency bands, the waveform difference caused by the weathered and oxidized zone is the most significant in the medium-frequency band (10-40 Hz). The lower boundary of the weathered and oxidized zone in the study area is distributed between the coal seam contour lines of 1 240 m and 1 260 m, being shallower in the east and deeper in the west, which is consistent with the exposure data of two boreholes in the study area. The Yuanyanghu-Fengjigou anticline exerts a remarkable influence on the development of the weathered and oxidized zone, and the boundary of the weathered and oxidized zone in the anticline core is near the 1 250 m contour line. Compared with the geological inference results, the measured weathered and oxidized zone is approximately 100 m shallower on the west side and 30-50 m deeper on the east side, with a minimum distance of about 160 m from the southern boundary of the work area. The noise autocorrelation method based on the subarray assumption can economically and efficiently detect weathered and oxidized zones in shallow-buried coal seams, and is suitable for wide popularization and application.

       

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