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

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