Measuring changes in fracture properties from temporal variations in anisotropic attenuation of microseismic waveforms

Philip Usher, J. M. Kendall, C. M. Kelly, A. Rietbrock

Research output: Contribution to journalArticle (Academic Journal)

4 Citations (Scopus)
222 Downloads (Pure)

Abstract

We investigate fracture-induced attenuation anisotropy in a cluster of events from a microseismic dataset acquired during hydraulic fracture stimulation. The dataset contains 888 events of magnitude −3.0 to 0.0. We use a log-spectral-amplitude-ratio method to estimate change in over a half-hour time period where fluid is being injected and an increase in fracturing from S-wave splitting analysis has been previously inferred. A Pearson's correlation analysis is used to assess whether or not changes in attenuation with time are statistically significant. P-waves show no systematic change in during this time. In contrast, S-waves polarised perpendicular to the fractures show a clear and statistically significant increase with time, whereas S-waves polarised parallel to the fractures show a weak negative trend. We also compare between the two S-waves, finding an increase in with time. A poroelastic rock physics model of fracture-induced attenuation anisotropy is used to interpret the results. This model suggests that the observed changes in t* are related to an increase in fracture density of up to 0.04. This is much higher than previous estimates of 0.025 ± 0.002 based on S-wave velocity anisotropy, but there is considerably more scatter in the attenuation measurements. This could be due to the added sensitivity of attenuation measurement to non-aligned fractures, fracture shape, and fluid properties. Nevertheless, this pilot study shows that attenuation measurements are sensitive to fracture properties such as fracture density and aspect ratio.
Original languageEnglish
Pages (from-to)347-362
Number of pages16
JournalGeophysical Prospecting
Volume65
Issue numberS1
Early online date10 Oct 2017
DOIs
Publication statusPublished - Dec 2017

Keywords

  • Attenuation
  • Fractures
  • Microseismic monitoring

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