基于压裂施工曲线小波变换的裂缝诊断及井筒完整性预测方法

Fracture Diagnosis and Wellbore Integrity Prediction Method Based on Wavelet Transform of Dynamic Fracturing Responses

  • 摘要: 四川盆地筇竹寺组页岩气井压裂过程中套管变形问题突出,严重破坏井筒完整性、影响单井产能,而现有裂缝诊断方法在实时性和动态性上存在明显局限。为解决这一问题,引入多尺度离散小波变换方法,以压裂施工压力曲线为研究对象,构建裂缝增长特征实时诊断模型,结合微地震监测数据判断人工裂缝与天然裂缝的沟通状态,实现压裂过程中套管变形的实时预警。通过对比不同Daubechies小波基及分解层级的特征提取效果,优选db4小波基作为最优诊断基函数,确定4~6级中低频带为核心特征频段,构建细节能量方差、最大绝对波动幅度为核心的量化预警判据。以JY5HF井为实例,将该方法与Nolte-Smith经典诊断方法对比,结合泵送桥塞、扫塞遇阻数据及微地震监测结果验证了模型有效性。结果表明,该方法与经典方法皮尔逊相关系数达0.86,可有效剔除工程噪声,精准识别即时套变与滞后套变的不同诱因,区分天然裂缝沟通与设备干扰信号。研究表明,该方法无需额外增加监测设备,成本低、实时性强,可实现“压前预测—压中诊断—压后验证”的井筒完整性一体化评估,为页岩气井压裂施工的安全高效开展提供技术支撑。

     

    Abstract: Targeting the frequent casing deformation issues during volume fracturing in unconventional reservoirs, it is urgent to establish an efficient real-time early warning mechanism to accurately reveal the dynamic communication between hydraulic and natural fractures, thereby preventing wellbore instability caused by excessive fracture aggregation near the wellbore. The multi-scale discrete wavelet transform (DWT) theory was introduced to denoise and analyze the high-frequency fracturing signals in the time-frequency domain. Combined with the Nolte-Smith diagnostic theory and downhole microseismic monitoring data, a dynamic fracturing analysis and fracture growth feature extraction model based on frequency-band energy characteristics was constructed. Field applications in typical gas wells show that the model can accurately capture and quantify the energy mutation signals of fractures in the time-frequency domain. It effectively extracts the abnormal growth features of complex fracture networks (e.g., fault activation and uncontrolled fracture height), thereby achieving real-time diagnosis and early warning of casing deformation risks. The research indicates that this diagnostic and prediction method not only overcomes the poor real-time performance of traditional approaches but also significantly improves the monitoring capability of wellbore integrity during fracturing. It provides reliable engineering support for the dynamic optimization of fracturing parameters and the prevention of casing damage in the field.

     

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