Estimation of shear wave velocity (Vs) in seismic studies of hydrocarbon reservoirs is very important. In this study, Vs is estimated in one of the hydrocarbon carbonate reservoir in an oilfields at southwest of Iran.
For 32 core plugs bulk density, grain density, porosity, permeability, compressional and shear wave velocities were measured. Elastic wave velocity measurement conducted in both dry and saturated samples under reservoir condition. Detailed petrographical studies carried out for all samples. Petrophysical parameters such as volume of shale and porosity were determined from corrected gamma ray log (CGR) and neutron and density logs respectively.
Shear wave velocity has been estimated as a function of compressional wave velocity, obtained from sonic log, lithology, porosity, volume of shale and formation pressure.
By comparison between estimated Vs, calculated by different relationships for carbonate rocks, with laboratory results, it is concluded that equations of Castagna & Greenberg (1992) and Castagna (1993) give good results.
In this study, improved new equations are also presented for estimation of Vs from Vp as follow :
Vs= 0.5243 Vp + 0.0451 Linear model (R2=0.84)
Vs= -0.1068 Vp2 +1.5106 Vp – 2.2008 Square model (R2=0.85)
In order to improve the above relationships, we verified sensitivity of these velocities to some parameters including: lithofacies, porosity type, volume of shale, depositional environments and the amount of porosity.