Modeling geomechanical property changes using well logging and pressure data in a CO2 enhanced oil recovery reservoir

Abstract

In order to better investigate the geomechanical property changes and rock failure taking place as a result of CO2 injection in the Delhi Field. The changes in compressional and shear velocity due to the CO2 injection needs to be taken into consideration. Several methodologies have been applied to synthesize compressional and shear velocity logs throughout the study field before and after the CO2 injection. A neural network approach was used as an alternative way to extrapolate the sonic log to any well location in the field before the CO2 injection. Eberhart-Phillips correlation was utilized to calculate the velocity changes as a result of pore pressure increase. The Gassmann equation was then applied to calculate the effect of CO2 saturation on velocity changes. As Eberhart-Phillips only takes into account the effective stress effect, the Gassmann equation only considers the CO2 saturation under constant stress. A new empirical equation coupling the CO2 saturation and pore pressure effect has been introduced. The results have been calibrated with time-lapse seismic derived sonic velocity. 3D characterization of geomechanical properties and strength at various effective stress scenarios has been evaluated. The rock properties obtained from the core measurement have been input into the 3D geomechanical model to predict the cap rock integrity and rock failure. The prediction indicates that no failure occurs in the study field based on CO2 injection pressure.