煤矿区钻孔瞬变电磁人工智能反演关键技术

Key technologies for artificial intelligence-based inversion of the borehole transient electromagnetic method in coal mining areas

  • 摘要: 背景钻孔瞬变电磁法凭借定向钻孔实现孔内近场激发与三分量同步接收,能够有效避免巷道内铁磁性物质的干扰,从而显著提升探测精度与范围,被广泛应用于煤矿井下隐伏水害探测。目前钻孔瞬变电磁反演方法在精度与效率上存在矛盾,现有技术难以同时满足隐伏水害探测高效性与高精度的需求。方法针对这一问题,提出一种基于贝叶斯优化的自适应样本构建方法与长短时记忆神经网络(LSTM)人工智能反演框架。首先通过趋势面法对实测数据理论响应进行重构,以减少环境等因素对数据的影响,为与模拟数据进行分布一致性分析奠定基础;然后引入贝叶斯优化策略,利用最大均值差异(MMD)与曲线下面积(AUC)构建分布一致性目标函数,该函数能够定量评估模拟样本数据与实测数据的分布相似性,从而不断优化确定最优电阻率区间。并研发了基于GPU并行计算的瞬变电磁一维正演算法,利用该算法依据最优电阻率区间构建高质量训练样本库。反演模型基本单元采用LSTM构建的Seq2Seq架构,并融合注意力机制(Attention)充分捕捉电磁响应的时序动态特征。并在一维反演的基础上,利用K-means聚类算法对水平分量异常特征的象限位置进行分类,在推导出的深度系数与电阻率的关系和求得工具面角信息的基础上,实现钻孔瞬变电磁反演电阻率立体成像。结果和结论在数值模拟实验中,该反演方法的平均相对均方根误差可控制在5%以内,相较于OCCAM反演与RNN反演方法表现出更高的精度。同时,通过抗噪性实验验证表明,在一定强度噪声干扰条件下,该方法仍能保持较好的稳定性与鲁棒性。在水槽物理模拟实验验证中,通过铜板代替低阻异常体,利用构建的高质量样本库和ATT-LSTM反演框架能精准反演出地层模型,并刻画出异常体的位置。通过新疆某煤矿工程实践应用表明,该方法可有效识别煤矿井下低阻异常区,立体成像结果与已知地质资料高度吻合,研究结果可为煤矿区隐伏水害探测提供可靠技术支撑,有效保障巷道高效、快速掘进。

     

    Abstract: Background The borehole transient electromagnetic method, which utilizes directional drilling to achieve near-field excitation and three-component synchronous reception within the borehole, can effectively avoid interference from ferromagnetic materials in the roadway, thereby significantly improving detection accuracy and range. It is widely applied to detect concealed water hazards ahead of excavation faces. Traditional borehole transient electromagnetic inversion methods face a trade-off between accuracy and efficiency, making it difficult for existing technologies to meet the demands of high efficiency and high accuracy for concealed water hazard detection in rapid excavation faces. Abstract: Background Using directional boreholes, the borehole transient electromagnetic (TEM) method enables near-field excitation and the simultaneous reception of three components within a borehole. This method can effectively avoid interference from ferromagnetic materials in roadways, thereby significantly enhancing the detection accuracy and range. Therefore, this method is widely applied to the detection of underground concealed water hazards in coal mines. However, there is a conflict between the accuracy and efficiency of current inversion methods for borehole TEM data, and existing technologies are insufficient to simultaneously meet the demands for high efficiency and high precision in the detection of concealed water hazards. Objective and Methods To address these issues, this study developed an adaptive sample construction method based on Bayesian optimization and established an artificial intelligence-based inversion framework using a long short-term memory (LSTM). Specifically, the theoretical responses of measured data were reconstructed using the method of trend surface analysis first, aiming to reduce the impacts of factors such as environment on the data and lay the foundation for the analysis of the consistency between the distributions of measured and simulated data. Then, the Bayesian optimization strategy was introduced, and the objective function for data distribution consistency was constructed using maximum mean discrepancy (MMD) and area under the curve (AUC). This objective function allows for the quantitative evaluation of the similarity between the distributions of simulated sample data and measured data, thereby contributing to the determination of the optimal resistivity range through continuous optimization. Furthermore, an algorithm for the one-dimensional (1D) forward modeling of TEM data was developed based on graphics processing unit (GPU) parallel computing. This algorithm was employed to construct a high-quality training sample database based on the optimal resistivity range. The basic framework of the inversion model incorporated the Seq2Seq architecture established using a LSTM while also integrating the attention mechanism to fully capture the temporal dynamic characteristics of electromagnetic responses. Based on 1D inversion, the quadrants of the anomalous response characteristics of the horizontal components of borehole TEM data were determined using the K-means clustering algorithm. Based on both the derived relationship between the depth coefficient and resistivity and the acquired information on toolface angles, the 3D resistivity imaging of the inversion results of borehole TEM data was achieved. Results and Conclusions Numerical simulation experiments reveal that the ATT-LSTM inversion yielded average relative root mean square errors (RRMSEs) of 5% or less, exhibiting higher accuracy compared to the Occam's inversion and the recurrent neural network (RNN)-based inversion. Noise resistance experiments indicate that the ATT-LSTM inversion method maintained high stability and robustness under noise interference at certain levels. Physical simulation experiments were conducted using a water tank, with a copper plate utilized as a substitute for a low-resistivity anomaly. The experiment results indicate that the constructed high-quality sample database and the ATT-LSTM inversion framework jointly allow for the accurate inversion of the stratigraphic models and the characterization of the low-resistivity anomaly. The engineering practice in a coal mine in Xinjiang demonstrates that the ATT-LSTM inversion method can effectively identify underground low-resistivity anomaly zones, with the 3D imaging result highly consistent with known geological data. Overall, the results of this study will provide reliable technical support for the detection of concealed water hazards in coal mining areas, thereby effectively ensuring efficient and rapid roadway excavation.

     

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