在水力压裂过程中,通过使用井中或者地表地震检波器来监测压裂诱发的微地震来确定裂缝的分布,并进一步评估压裂储层的改造体积.在四川德阳的一次水力压裂微地震监测实验中,通过对记录的波形进行时频分析,确定了不同频率共振信号的变化情况.对于~13 Hz共振信号来说,根据它的强度变化可以推断信号产生于地表井场.进一步对井场处机械噪声的激励和响应进行分析,认为信号的来源是高压管线的强烈振动,激振源为三缸泵的周期性冲程造成的流体中的压力脉动.因此利用微震监测得到的共振信号,可以用来分析监测高压管线的振动情况.%During hydraulic fracturing, induced microseismic events are generally monitored by surface or downhole geophones to determine their locations from which the stimulated reservoir volume can be estimated. In a surface microseismic monitoring experiment carried out in Deyang of Sichuan province, microseismic events are not detected due to strong near surface attenuation and background noise. Instead, we detected continuous signals with stable resonance frequencies, which are well correlated with slurry flow. This kind of signals have been detected in other hydraulic fracturing monitoring cases and are interpreted as the Stonley waves by the interaction of high-pressure fluids with the surrounding fractures (Tary et al., 2014). In our case, through the time-frequency analysis we can obtain how frequency and amplitude of these resonant signals change with time at different stations. For the ~13 Hz resonant signal, its amplitude generally decreases at stations farther away from the well site, indicating that the signal is most likely originated from the surface well site. As a result, by using these stable resonant signals, it could provide us a way to monitor the vibration condition of high-pressure pipes used for hydraulic fracturing. Based on these facts, we propose that these resonant signals are caused by vibrations of high-pressure pipes triggered by periodic pressure pulses of triplex pumps. We further suggest that the interpretation of these resonant signals due to Stonely waves or nonlaminar flows by Tary et al. (2014) may be wrong based on several contradictive points with observations. They are also likely caused by vibrations of high-pressure pipes, similar to what we derived from our experiments.
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