Seismic modelling of fractured carbonate reservoirs
M.Y. Ali, M. Worthington (Oxford University)

Summary

 

The main objective of this work is to establish whether seismic anisotropy within the vicinity of a well (or wells) determined from surface reflection seismic or passive seismic data is consistent with data obtained from core and/or well logs. The work includes:

  1. Analysis of FMS and P and S wave sonic logs to obtain estimates of fracture density, orientation and aperture and P and S wave velocity and velocity anisotropy.
  2. Determination of fracture compliance from the results from 1.
  3. Determination of the most appropriate 2-D and 3-D statistical models of fracture distribution from existing published theory and from local outcrop and reservoir studies.
  4. Seismic modelling of a fractured reservoir based on the results from 1, 2 and 3.
  5. Interpretation of the modelled and observed seismic anisotropy to establish levels of confidence in the prediction of reservoir stress field distribution and fluid flow from regional seismic attributes.
  
     

 
Fig. 1. Cretaceous carbonates in Oman Mountains showing intense fracturing.

 

Fig. 2. Variation of P wave Vnmo with azimuth for three reservoir fracture models, (1) green: one fracture set with normal compliance of 1.0 ´ 10-12 Pa-1 (2)blue: two fracture sets striking at N040E and N070E and with normal compliance of 1.0 ´ 10-12 Pa-1(3) red: as blue but with maximum normal compliance of 6.0 ´ 10-12 Pa-1.Note that the maximum velocities are in the mean fracture strike direction, N040E for green and N055E for blue and red.