Microscopic experimental of oil-water mutual driving of the low permeability reservoir:taking the Lulehe formation in the H area of the Qaidam basin as an example

The microscopic characteristics of oil-water mutual driving in the process of water flooding development of the low permeability reservoir are really complex.Taking the Lulehe formation reservoir in the H area of the Qaidam basin as an example, based on the thin slice observation, scanning electron microscope(SEM), physical property analysis and mercury pressure test, the oil-water mutual driving microscopic characteristics are comprehensive studied.It shows that the reservoirs are mainly composed of lithic arkose sandstones and arkoses with poor property and strong heterogeneity.Reservoir space is dominated by primary intergranular pores that are characterized by wide distribution, poor sorting, multiple distribution types and dispersal.In the reservoir, the flow of crude oil is non-darcy seepage, and the start-up pressure gradient is reduced along with the increase of the permeability, but the correlation is poor.Linear flow of single-phase seepage occurres after increasing the pressure gradient.It is the non-uniform displacement process with strong heterogeneity and low original oil saturation.Water flooding breakthrough rapidly along one or two channels, water-free oil production period is short, the efficiency is low.The water displacement efficiency can increase by the pressure, but the effect is not obvious.The residual oil types are flow around oil, oil film and the residual oil at the edge of the corner, the formation mechanism is different.