(140d) Analytical Modeling of the Forced Gravity Drainage Gagd Process

Literature review on gravity drainage suggests that the fundamental understanding and modeling of the gravity drainage process is still a challenge to the reservoir engineer, mainly because of the limitations of the reservoir simulation tools, to better include the physics of the process into improved reservoir management. This paper attempts to identify the fundamental forced gravity-drainage mechanisms, and possibly improve the mechanistic understanding of gravity-drainage processes by conducting: (i) mechanistic studies of the gravity-drainage process and (ii) employing analytical models to predict the recovery characteristics. Mechanistic studies on gravity-drainage suggested that the existing models employed the Buckley-Leverett and gravity-drainage theories to model forced and free gravity-drainage, respectively. It appeared that neither of these theories holistically characterizes our newly developed Gas-Assisted Gravity Drainage (GAGD) process, due to non-representative assumptions. A ?lumped' approach appeared to be preferable for GAGD modeling, and a new gravity-drainage mechanism has been proposed. Additionally, two ?lumped' mechanistic models, Richardson and Blackwell's analytical model (1971) and Li and Horne's empirical model for free gravity drainage (2003), were employed for validation of the proposed mechanism. The R&B model was validated against Hawkins Dexter field's gravity drainage flood data, and later employed to predict oil recoveries for 1-D and 2-D laboratory GAGD floods. The R&B model was found to predict the ultimate oil recovery within a 6.4% error band. The L&H model, used to predict the dynamic recovery characteristics due to R&B model limitations, was found to over predict the GAGD oil recoveries. To improve the capillary pressure modeling and incorporate the GAGD mechanisms into the model, the ?demarcator' concept of the original gravity drainage theory was introduced into the L&H model. This modification appears to have significantly and successfully improved the resulting model's ability to capture the multiphase mechanisms and fluid dynamics of gravity drainage processes.