Pressure data during and after hydraulic fracturing is routinely collected, yet typically it is not fully analysed. Fluctuations in treatment pressure may provide insights into the physical mechanisms at play during hydro-mechanically coupled movement of fluid in the subsurface. A time-frequency representation of surface pressure data from cases within the Western Canadian sedimentary basin reveals characteristic time-frequency patterns that may be causally linked with microseismicity and pressure transient observations. Integration of these distinct observations leads to various working models for observed time varying frequencies. Resonances within the fluid connected fracture network may develop and give an indication of the fluid connected length and mechanical aperture within the rock mass. Episodic slip or opening of the fracture mesh may create a valve-like behaviour, resulting in pressure spikes and low-frequency signals. Sources of noise and the limitations associated with typical treating pressure data are discussed and recommendations are presented to gain more value from this novel analysis technique.

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