This paper presents an investigation of gravity-driven flow in naturally fractured reservoirs via multiphase flow in angular capillary tubes. The study includes theoretical and numerical analyses, and is supported by laboratory measurements.
Gravity is important in many oil recovery processes, either acting as the driving force in processes using horizontal wells or altering displacement patterns during waterflooding, chemical flooding, CO2 flooding, and other EOR processes.
Gravity drainage driven oil production in naturally fractured and other complex reservoirs falls into two regimes: the bulk flow and the film/corner flow. After the bulk flow at constant production rate and a short period of transition, the corner/film flow dominates the production. The flow in the corners and films in fractures and pore-channels is the focus of this study. Modeling the flow channels as angular capillaries of variable polygon shapes provides a valid physical basis for corner flow.
The fluid distribution above the gas/oil contact is influenced by in-situ capillary force but more by the fluid dynamics. Numerical simulation of the film/corner flow was conducted for various cross sectional shapes using finite element analysis (FEA). Experiments were conducted using space between packing of glass rods as flow channels that capture the essential features of flow channels in rocks and natural fractures. Comparison between the simulation predictions and experimental observations allowed validation of the modeling process.
The results of this study provide basis for more detailed network models, which describe rock-fluid systems at microscopic level with deterministic solutions. The modeling procedure presented in this study and the results are useful for modeling the performance of gravity dominated improved oil recovery processes.