Applicability of Slug Flow Models to Heavy Oils

In oil production, an increasing amount of the oil being produced is considered heavy or extra heavy (0.1 to 10 Pa·s). To design systems to produce and transport this heavy oil and its associated gas requires an understanding of the multiphase flow characteristics. The multiphase models currently available are based on data from much lower viscosity fluids (0.001 to 0.02 Pa·s). Increasing the viscosity to that of heavy oil changes the characteristics of multiphase flow. The liquid flow, for example, is often laminar or in the transition region from laminar to turbulent.

Slug flow and closure relationship data for heavy oils have recently become available in the literature for both horizontal and vertical flow. This laboratory data allows the testing of current modeling technology to understand modeling gaps that must be addressed. Simulations using typical slug flow models were performed at conditions where the liquid flow in the liquid slug and the liquid film are primarily laminar. The results show that this type of flow can be accurately described without major modifications to the models. The closure relationships such as distribution parameter, drift velocity, and holdup in liquid slug are discussed along with the impact of these choices. In many cases the holdup and pressure drop could be described within 10% or less. These findings have important implications for how heavy oil is modeled and what additional studies are still needed.