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.

Automated summary

This article examines the seepage characteristics and differential accumulation of crude oil in Chang 6 sandy-debris-flow and turbidite-current sandstones in the Ordos Basin using physical simulation experiments. The results indicate that the flow of crude oil in these sandstones is nonlinear and quasilinear, with threshold pressure gradient and critical pressure gradient. The turbidite-current sandstones exhibit a leap in oil saturation with relatively low maximum oil saturation, while the sandy-debris-flow sandstones show steady growth with high maximum oil saturation. Differential accumulation of crude oil is influenced by porosity, permeability, crude oil viscosity, and hydrocarbon-generating pressure. To accumulate, the pressure gradient needs to surpass the critical pressure gradient, which occurs when the oil saturation exceeds 25%. Large-scale oil accumulation easily occurs in near-source sandy-debris-flow sandstones, whereas in far-source deep-water sandstones inauthentic oil accumulation is more likely.