Analysis Of Non-microseismic Signals During Hydraulic Fracturing Of Tight Oil/Gas Reservoirs

Hydraulic fracturing is a widely implemented industrial performance to enhance production of tight oil or gas. It is carried out by injecting high-pressure fluid with proppant through well into target reservoir layers. To monitor the process of hydraulic fracturing, seismometers are set up on the ground surface or in boreholes to record microseismic events associated with hydraulic fracturing. By locating these events, the stimulated reservoir volume by hydraulic fracturing could be estimated. Meanwhile, seismometers or geophones can not only record target microseismic events, but also record various signals caused by different sources. In this thesis, I mainly focus on signals with resonance frequencies among non-microseismic signals. We will also have a brief discussion of some repeating signals. Tary et al. (2014) discussed the phenomenon about resonance frequencies detected during hydraulic fracturing. They identified two possible causes within the source area, namely, eigenvibrations of fractures or non-Darcian flow within the hydraulic fractures. In the first situation,15-30 m long fluid-filled cracks could generate the observed resonances. An interconnected fracture network would then be required, corresponding to mesoscale deformation of the reservoir. Alternatively, systematic patterns in non-Darcian fluid flow within the hydraulic fractures could also be possible. In this thesis, we ftirther discuss about this phenomenon in a broader way. On one side, we explore the vibration condition on the ground of tracking machinery, including the possible cause of pressure perturbation by triplex pump and corresponding response of high pressure pipe system. On the other side, we also explored the explanation by Tary et al. (2014) and discussed about the discrepancies between their theory and the reality. We believe these relative stable resonance frequencies observed by surface or deep downhole geophones corresponding to slurry flow are related to vibration of high pressure pipe system caused by nonstable flow triggered by triplex pumps, rather than by crack waves or nonlaminar flow. In addition to signals with resonance frequencies, we also briefly analyzed about some repeating signals with unknown sources. Based on the analysis of non-microseismic events, we need to carry out the study of optimizing distribution of surface seismometers in order to record target microseismic events. In practice, seismic monitoring of resonance frequencies could provide us a way to monitor vibrations of high pressure pipe system.