Abstract: The evaluation of temporary plugging effectiveness in horizontal well fracturing is a crucial method for enhancing the balance of unconventional oil and gas fracturing stimulation. Currently, downhole distributed optical fiber monitoring serves as a reliable technique for evaluating the effectiveness of temporary plugging. However, its widespread application across all wells is hindered by the high costs and operational complexity. This paper presents a method for identifying fracture propagation modes and evaluating the effectiveness of temporary plugging based on the time-frequency characteristics of pump pressures recorded at one-second intervals. Continuous wavelet transform is used to perform multi-resolution analysis of the pressure signals, extracting wavelet energy across various time and frequency domains to characterize the pressure fluctuations. The evaluation of temporary plugging effectiveness is achieved by identifying multi-fracture propagation modes before and after temporary plugging, which is based on the cumulative variation of wavelet energy. The results indicate that:(1)Continuous wavelet transform effectively amplifies subtle pressure fluctuations, successfully capturing the physical process in which pump pressure fluctuates frequently due to the fractures competition among multiple clusters, ultimately stabilizing when the primary fractures form. (2)Biorthogonal wavelet basis demonstrates strong frequency band division and main frequency identification capabilities, making it an optimal choice for continuous wavelet transform. The intensity of signal fluctuations varies with frequency. When the variation trends of pressure and slurry rate fluctuations diverge, the pressure fluctuations at the corresponding frequency can effectively distinguish between two fracture propagation modes, i.e., the fractures competition among multiple clusters and the formation of primary fractures. This frequency band can thus be selected as the basis for time-frequency analysis. (3)The transition of the wavelet energy accumulation trend from an upward to a stable state serves as a key criterion for identifying the process where multi-cluster fractures compete until primary fractures form. A moving average algorithm is employed to extract the cumulative wavelet energy trend. By applying a 60-second window and a 25 % quantile threshold for the rate of change, this method effectively distinguishes trend variations. (4)The occurrence of new fractures after temporary plugging can be classified based on the duration of multi-cluster fractures competition. Statistical analysis reveals that the classification threshold corresponds to the first 4.94 % of the total fracturing time after temporary plugging. This method was validated using data from 27 stages of distributed optical fiber monitoring, yielding a match rate of 96.30 %. Optimizing temporary plugging during the early stage of primary fractures formation can effectively enhance the plugging effectiveness for fracturing.

Key words: unconventional oil and gas, temporary plugging fracturing, balanced stimulation, evaluation of temporary plugging effectiveness, time-frequency analysis, continuous wavelet transform

摘要： 水平井压裂暂堵有效性评价是提升非常规油气压裂改造均衡性的重要途径之一。目前井下分布式光纤监测是评价暂堵有效性的可靠手段,但由于成本和操作复杂性,很难普及至每口井。为此,建立了基于泵注压力时频特征的压裂裂缝扩展状态及其暂堵有效性的判识方法,即采用连续小波变换对压力秒点数据进行多分辨率分析,提取不同时间与频率下的小波能量,刻画压力信号波动特征,通过小波能量累积变化判识暂堵前后多裂缝扩展状态,实现压裂暂堵有效性评价。研究结果表明:①连续小波变换能够有效放大压力微小波动,成功捕捉到泵注压力在多簇裂缝竞争下波动频繁,直至优势裂缝形成时趋于稳定的物理过程。②Biorthogonal小波基频带划分和主频识别能力强,可作为最优小波基;不同频率下的信号波动强度将发生变化,当压力与排量波动强度的变化趋势出现差异时,对应频率的压力波动能够有效表征多簇裂缝竞争与优势裂缝形成2类裂缝扩展状态的差异性,可作为时频分析频段。③小波能量累积趋势由上升转为平稳是多簇裂缝竞争到优势裂缝形成过程的重要判据,采用移动平均算法提取小波能量累积趋势,结合60 s窗口与变化率25 % 分位阈值能够有效区分趋势变化。④暂堵后是否出现新裂缝可通过多簇裂缝竞争持续时间分类表征。统计表明,分类阈值为暂堵后压裂总时长的前4.94 %,经27段分布式光纤监测数据验证,匹配度达96.30 % 。通过优选优势裂缝形成初期暂堵,可有效提升压裂暂堵有效性。

关键词: 非常规油气, 暂堵压裂, 均衡改造, 暂堵有效性评价, 时频分析, 连续小波变换