Influence of ultra-low interfacial tension system on nonlinear seepage law of low permeability core

Abstract

The starting pressure gradient in low permeability reservoir leads to the nonlinear characteristics of fluid flow, which makes the development mode of low permeability reservoir different from that of medium and high permeability reservoir.In order to study the nonlinear seepage phenomenon in the low permeability reservoir of Xinli Oilfield, taking the natural low permeability core of Xinli Oilfield as the research object, the influence of ultra-low interfacial tension system on the start-up pressure gradient of single-phase and two-phase fluid in Xinli low permeability cores was analyzed through the porous media seepage experiment of precision pressure tests.The results show that for any fluid, the low permeability core of Xinli Oilfield shows nonlinear seepage characteristics, and there is a certain threshold pressure gradient.The value of pseudo starting pressure gradient of low permeability cores is higher than that of starting pressure gradient, and both of them decrease with the increase of permeability, and the relationship between them is power.The ultra-low interfacial tension system can obviously reduce the minimum starting pressure gradient and quasi starting pressure gradient of low permeability cores.For cores with different permeability, the relationship between the two-phase critical starting pressure gradient and water saturation shows a similar change law, that is, the two-phase critical starting pressure gradient firstly increases and then decreases with the increase of average water saturation.Under different permeability, the highest critical pressure gradient of water flooding and ultra-low interfacial tension system flooding is compared.The highest point of critical pressure gradient in ultra-low interfacial tension system is obviously smaller than that in water flooding.This shows that the decrease of interfacial tension can significantly reduce the two-phase critical pressure gradient during oil displacement, and the ultra-low interfacial tension system improves the injectivity of the reservoir.This study provides a reference for the selection of development mode after water flooding in Xinli low permeability reservoir.

Keywords

• ultra low interfacial tension
• starting pressure gradient
• porous media seepage
• single phase and two phase flow