Applications of Seismic Interferometry in Microseismic Monitoring

• Author / Creator

  Vaezi, Yoones

• Microseismic monitoring involves the acquisition of continuous seismic data for the purpose of locating and characterizing microseismicity induced mainly by oilfield completion and production processes. Since its inception, microseismic monitoring has proved to be an invaluable tool for understanding underground processes and monitoring subsurface changes associated with hydraulic fracturing, steam stimulation, geothermal energy production, underground deep mines, and CO2 storage and sequestration. Different existing and emerging new techniques are progressively being employed by the microseismic monitoring industry to provide an even more detailed and comprehensive analysis of the available data. This thesis focuses on potential applications of seismic interferometry in microseismic monitoring, a rather new method which has shown extensive applications in exploration geophysics and global seismology. Seismic interferometry mainly refers to a technique used for recovering the Green's function between two receivers by crosscorrelating their passive seismic noise recordings, thereby emphasizing the coherent part of noise which is deeply buried under local seemingly incoherent noise. We have used this property to obtain body waves propagating along borehole geophones deployed in downhole microseismic experiments, and therefore, obtain the associated seismic velocities at the neighboring formations surrounding the wellbore at the intervals between the geophons. Whether or not the coherent body waves appear clearly on the crosscorrelation functions depends on the instrument self-noise and clamping quality of borehole geophones. By obscuring the coherent noise of interest, instrument self-noise levels that are comparable with or above background noise levels can challenge seismic interferometry which aims at analysis of coherent features in ambient noise wavefelds to reveal subsurface structure. Such high levels of instrument self-noise can also act as a major constraint for the detection of weak microseismic events, in particular for borehole deployments in quiet environments such as below 1.5-2 km depths. Estimates of the instrument self-noise are commonly approximated by power spectral densities at the quiet times. The power spectral densities can also themselves be used as a tool for microseismic event detection as such events typically represent stronger spectral content over a frequency band than that of the background noise. This technique outperforms the common event detection method of short-time average/long-time average by detecting a higher number of weak events while keeping the number of false alarms at a reasonable level. It also has the benefit of providing suitable bandpass filters for better picking and further analysis of the events. On the other hand, the characteristics of the retrieved crosscorrelation waveforms can give insights about the coupling quality of the geophones to the wellbore wall as better coupled arrays result in body waves reconstructed up to a higher frequency range when compared with poorly clamped geophone arrays. We also study the potential application of coda wave interferometry for monitoring purposes in a surface microseismic monitoring setting, specifically for a wastewater disposal well. Significant changes in the fluid injection pressure into the underground reservoir can have direct impacts on the seismic velocity variations. The relative velocity variations are estimated by a recently developed version of the coda wave interferometry, known as passive image interferometry, using the time shifts between consecutive correlation functions.

• Subjects / Keywords

  • Passive image interferometry
  • Microseismic event detection
  • Instrument self-noise
  • Coda wave interferometry
  • Seismic interferometry
  • Geophone clamping quality
  • Microseismic monitoring

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R39S1KQ9R

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.