Oil secondary migration simulation in tight reservoir and fingering factors analysis

Abstract

In the tight reservoirs, the oil accumulation is characterized by ambiguous trap boundaries, complicated oil distribution and nano-scale pore-throat interconnection system. As one of significant process for understanding the oil trap in the tight reservoir, oil migration from source rocks to reservoirs is the key concern by geoscientist. Investigating the immiscible two-phase fluids displacement in porous media, especially the fingering problem during the hydrocarbon migration, has always been a challenge scientific topic. This study establishes PNMs (Pore Network Model) with multiple viable parameters. A fluid migration numerical program is built for the flow study by modifying Poiseuille equation. Sensitive studies have been conducted by several dimensionless numbers to investigate the control factors of the flow behavior. Five factors are identified as the key factors on the migration mode: 1) Fluid viscosity ratio; 2) Interface tension force; 3) Fluid density; 4) Pore structure of sediments; 5) Capillary number. Oil migration behavior is affected by pressure domain, buoyancy, and resistance forces, such as capillary resistance and viscous forces. As the distribution fractal dimension increases with a given viscosity ratio, the width of the front edge of oil-water interface gradually expands. Oil saturation increases in parallel with a rising capillary number. During the simulation, Haines Jump phenomenon is observed. When the capillary number increases, oil migration gravitates towards piston-like displacement. As the oil-water viscosity ratio increases, the front width reaches its maximum at a particular point in time, and plateaus.