Fracture characterization using frequency-dependent shear wave anisotropy analysis of microseismic data

O. H. Al-Harrasi*, J M Kendall, M. Chapman

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

34 Citations (Scopus)

Abstract

The presence of fractures in hydrocarbon reservoirs can enhance porosity and permeability, and consequently increase production. The use of seismic anisotropy to characterize fracture systems has gained much interest in the last two decades. However, estimating fracture sizes from observations of seismic anisotropy has not been possible. Recent work has shown that frequency-dependent anisotropy (FDA) is very sensitive to the length-scale of the causative mechanism for the anisotropy. In this study, we observe FDA in a microseismic data set acquired from a carbonate gas field in Oman. The frequency-dependent shear wave anisotropy observations are modelled using a poroelastic model, which considers fluid communication between grain size pore spaces and larger scale fractures. A grid search is performed over fracture parameters (radius, density and strike) to find the model that best fits the real data. The results show that fracture size varies from the microscale within the shale cap rocks, to the metre-scale within the gas reservoir, to the centimetre-scale within the non-producing part of the carbonate formation. The lateral variation in fracture density agrees with previous conclusions from ordinary shear wave splitting (SWS) analysis. Cumulatively, the results show the potential for characterizing fracture systems using observations of FDA.

Original languageEnglish
Pages (from-to)1059-1070
Number of pages12
JournalGeophysical Journal International
Volume185
Issue number2
DOIs
Publication statusPublished - 1 May 2011

Keywords

  • Downhole methods
  • Fracture and flow
  • Seismic anisotropy

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