Crude oil differential enrichment in sandy-debris-flow and turbidite-current sandstones by physical simulation experiment

The article selected the samples of Chang 6 sandy-debris-flow and turbidite-current sandstones in the Ordos Basin and studied the seepage law and differential accumulation of crude oil by physical simulation experiment. The results show that the sandy-debris-flow and turbidite-current sandstones are featured with nonlinear and quasilinear crude oil flow with the threshold pressure gradient and critical pressure gradient. The oil saturation increases by leaps in the turbidite-current sandstones with relatively low maximum oil saturation. The sandy-debris-flow sandstones show steady growth with high maximum oil saturation. Differential accumulation of crude oil is controlled by porosity, permeability, crude oil viscosity, and hydrocarbon-generating pressure. The crude oil accumulation requires the pressure gradient to break through the critical pressure gradient, which can be formed if oil saturation exceeds 25%. Large-scale oil accumulation is easily formed in near-source sandy-debris-flow sandstones. Far-source deep-water sandstones easily develop inauthentic oil accumulation.