f Kamali - Petroleum U. of Technology
r Kharrat - Petroleum U. of Technology
b Rostami - Sharif / Petroleum U. of Technology
S. H. Tabatabaei

The Gas Assisted Gravity Drainage (GAGD) process was developed as an alternative to the currently popular water-alternating-gas process. Multiphase mechanisms and fluid dynamics operational have been found to be important, to facilitate forecasting of the reservoir behavior and oil recovery characteristics. Therefore, it is important to have good knowledge of dominant forces (viscous, capillary and gravity) during the production life.By considering of three chief forces in oil recovery process, the mathematical formulation takes the form of a nonlinear convection-diffusion equation. Thus, a numerical model based on the finite-difference formulation was implemented to obtain the solution of this equation and it can be used to simulate more complex two-phase flow problems. In the GAGD process, the flow regimes will be varied by changing the gas injection rate. In this circumstance, the gravity drainage assumptions should be verified when the process moves from the gravity-capillary dominant regime to the capillary-viscous dominant regime. Since, ignoring gas mobility is the most popular assumption in gravity drainage process; in such a forced gravity drainage GAGD process, this assumption may not be valid.In this paper, sensitivity analysis on gas mobility and gas injection rate in gas gravity drainage was done around the critical rate that mechanistically represents the maximum injection rate at which the gravity forces are dominant. The results show when the gas velocity is less than the gravity-stabilized rate, gas mobility may still be assumed infinite. In addition, when the gravity force is overcome by the increased magnitude of viscous forces (gas injection rate) the alteration of gas mobility could highly influence on oil recovery

Gravity drainage, viscous, capillary, gravity force, gas injection rate and relative permeability