Modifying Greenberg-Castagna Empirical Relationships to Predict Shear Wave Velocity in an Oil Bearing Reservoir of South-West Iran

Shear wave velocity provides petroleum engineers with the valuable information to manage efficient processes in the development of hydrocarbon reservoirs. Shear wave velocity (Vs) plays a prominent role in characterizing some important reservoir properties such as lithology, pore fluid type, productive zone, etc. Since using well logging is too expensive, Vs is not available in all wells. In this case, a wide variety of empirical relationships have been published for different lithologies in which Castagna and Greenberg are of the first rank. Greenberg and Castagna (1993) have given empirical relationships in multiminerslic, brine-saturated rocks based on representative polynomial regression coefficients for pure lithologies represented by Castagna. In addition, Gassman relationships should be applied to fulfill assumption of brine saturation. The present study carried out in an Asmari reservoir of an oil field in Sothwest Iran which has a Vs log. In the present paper, firstly, Gassman relationships are applied to replace the common fluid. So compressional wave velocity (Vp) is calculated in the condition of brine saturation. Note that, Greenberg-Castagna relationships are empirical and should be modified for the studied reservoir. This modification done in two different phases due to lithology and water saturation. Finally, regression coefficients of Castagna used for prediction of Vs in limestone and shale. Also, regression coefficients of first and second modifications are respectively used for dolomite and sandstone to predict the Vs. According to results, correlation coefficients between real and predicted values are 0.84 and 0.94 respectively before and after modification, which prove the superiority of modified model of Greenberg-Castagna.