Experiment Research on Starting Pressure Gradient of Oil-Water Two Phase Flow in Cores
Low permeability reservoirs have starting pressure gradient in the oil-water phase seepage,fully understanding the change and influence factor of starting pressure gradient in water driving oil.In order to get a thorough understanding of starting pressure gradient's characteristic and influence factor in oil-water phase seepage,the starting pressure gradients of different permeability,different water saturation and different wettability cores in two-phase seepage during water flooding were experimentally measured in laboratory,according to the experimental phenomenon,resistance effect and microgenesis generating starting pressure in the cores'hole have been analysed.The result of research shows that the starting pressure gradients of cores that permeability below 50 × 10-3μm2 are incremental with water saturation growing.The starting pressure of cores that permeability above 50 × 10-3 µm2 don't change much with the permeability changing,and the whole trend is declining,the values of starting pressures are small.For low permeability reservoirs,the cores permeability and wettability index are smaller,the boundary layer thickness are larger,the starting pressure gradients are larger.The adding resistance effects producing starting pressure gradient have the frictional drag caused by oil drop capillary pressure,the resistance caused by oil bead deformation from static wetting lag and the resistance caused by liquid resistance effect,whose values are related to pore throat radius,wettability index,oil and water distribution in microscopic pores,boundary layer thickness and solid-liquid interfacial tension.
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