基于功率谱密度差异的煤层水力压裂微震信号识别及缝网演化特征

Microseismic signal recognition based on power spectral density differences and fracture network evolution in coal seam hydraulic fracturing

  • 摘要: 针对强噪声背景下水力压裂微震信号识别精度不足及缝网演化特征难以可靠刻画的问题,基于榆树田煤矿现场水力压裂微震监测数据,开展煤层水力压裂微震信号识别方法与缝网空间演化规律研究。通过揭示微震事件与典型噪声信号在主频能量集中特性、谱平坦度与谱振荡指数上的本质差异,构建了融合多尺度时频深度卷积特征与功率谱密度(PSD)统计特征的双分支信号识别新框架。测试结果显示,双分支联合特征模型在准确率、召回率和F1值上均显著优于单一PSD统计特征模型:平均准确率由0.83提升至0.93,召回率由0.79提升至0.92,F1值由0.80提升至0.92。在完成模型验证后,将该模型应用于榆树田现场全段压裂微震监测数据,最终从原始连续波形中有效识别出581个水力压裂微震事件,为后续破裂空间结构刻画提供了高可信数据基础。在震源定位方面,本研究采用快速地震关联定位方法(REAL),利用P/S波检波点数量与到时残差协同构建事件关联关系,并结合高精度相对定位法对结果进一步优化。REAL方法的引入显著提升了微震序列的定位效率,使得压裂事件的三维展布得以清晰约束。震源定位与缝网分布结果显示,不同压裂段间缝网规模与几何复杂度差异显著,裂缝网络整体呈NW-SE(约320°~340°)主方向展布,并伴随NE-SW(约40°~70°)次方向分支,反映了区域构造节理与地应力场的共同控制作用。在储层改造体积(SRV)量化方面,全部压裂段SRV值为318.1×104 m3。其中第8段SRV最大(45.2×104 m3),第6段与第7段亦形成较大的改造体积,而第1段与第9段SRV明显偏低,事件密度与SRV整体具有较强一致性。

     

    Abstract: To address the low accuracy of microseismic signal identification and the difficulty in reliably characterizing fracture network evolution under strong noise conditions, field microseismic monitoring data from hydraulic fracturing at the Yushutian coal mine were used to investigate signal identification methods and fracture network spatial evolution in coal seams. By revealing the intrinsic differences between microseismic events and typical noise signals in terms of dominant frequency energy concentration, spectral flatness, and spectral oscillation index, a dual-branch signal identification framework was developed by integrating multi-scale time–frequency deep convolutional features with power spectral density (PSD) statistical features. The results show that the dual-branch model outperforms the single PSD-based statistical feature model in terms of accuracy, recall, and F1-score, with the average accuracy increasing from 0.83 to 0.93, recall from 0.79 to 0.92, and F1-score from 0.80 to 0.92. After model validation, the framework was applied to the full-stage hydraulic fracturing microseismic dataset at the Yushutian site, and a total of 581 microseismic events were identified from continuous raw waveforms, providing a reliable dataset for subsequent characterization of fracture spatial structures. For hypocenter determination, the rapid earthquake association and location (REAL) method was employed, in which event associations were established using the number of P/S-wave picks and arrival-time residuals, and the results were further refined using a high-precision relative location method. The introduction of the REAL method improves the location efficiency of the microseismic sequence and constrains the three-dimensional distribution of fracturing events. The hypocenter locations and fracture network distribution indicate that the scale and geometric complexity of fracture networks vary among different fracturing stages; the fracture network is predominantly oriented in the NW–SE direction (approximately 320°–340°), with secondary branches in the NE–SW direction (approximately 40°–70°), reflecting the combined control of regional structural joints and the in-situ stress field. In terms of stimulated reservoir volume (SRV) quantification, the total SRV of all fracturing stages is 318.1×104 m3. Among them, Stage 8 exhibits the largest SRV (45.2×104 m3), followed by Stages 6 and 7, whereas Stages 1 and 9 show relatively low SRV values; the spatial density of microseismic events is generally consistent with the SRV distribution.

     

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