Abstract
Cold heavy oil production exploits the mechanism of enhanced solution gas (or foamy-oil) drive to achieve an economic oil flow rate and ultimate recovery. Understanding the dynamics of foamy-oil drive and being able to simulate the process make it possible to evaluate the potential of cold production more realistically.
A generic kinetic model based on known solution gas exsolution and evolution process has been proposed and tested. The sequence of gas exsolution in foamy-oil drive can be described by the following four major steps and corresponding (first-order) mechanisms:
Supersaturation from pressure drawdown
Bubble nucleation under super-saturation
Bubble growth under molecular diffusion
Bubble coalescence from film drainage
The effects of dispersed gas on the gas phase mobility has been modeled with a simple viscosity mixing rule by assigning a much higher viscosity to the dispersed gas component. The benefits of this approach is that the apparent low mobility of the gas phase in the foamy-oil drive process can be attributed to the viscosity change, instead of rate dependent relative permeability. Therefore, a “normal” relative permeability can be used for a wide range of rate conditions.
The proposed dynamic model has been validated with the history matches of both the volume draw down and the pressure draw down laboratory test data. The validation reveals that one can use a set of consistent dynamic parameters to match the results of various tests under different draw down rates.
The dynamic model has been implemented in a commercial reservoir simulator (CMG-STARS) with available options.
