Study on the influence of the viscosity reducer solution on percolation capacity of thin oil in ultra-low permeability reservoir

Abstract It is a new field to improve oil recovery by reducing the viscosity of thin oil in low permeability reservoir, which has a breakthrough significance for the development of low permeability oilfield. But, the oil increase effect of viscosity reducer (VR) solution on thin oil lacks the experimental data and theory support. The viscosity of ground degassed crude oil from the thin oil reservoir is 26.4 mPa s at 72°C. The feasibility of the application of VR solution in thin oil reservoir was analyzed through the experiment and test of viscosity reducing ability, percolation capacity, and displacement effect of VR solution. The oil–water ratio is 5:5, the VR concentration ( C VR ) of oil–water dispersion (OWD) solution is 0.1%, and the viscosity reduction rate of VR solution reaches 92.4%. The maximum instantaneous injection pressure ( P max ) of the VR solution injected with the C VR of 0.1% is the lowest, which is 6.60 MPa, the P max decreases by 0.83 MPa than the P max in the basic water flooding experiment, the injection pressure in stable stage ( P min ) decreases by 0.80 MPa. When the bound water saturation <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mo stretchy="false">(</m:mo> <m:msub> <m:mrow> <m:mi>s</m:mi> </m:mrow> <m:mrow> <m:mtext>wi</m:mtext> </m:mrow> </m:msub> <m:mo stretchy="false">)</m:mo> </m:math> ({s}_{\text{wi}}) of core is 41.1%, the VR solution is directly injected before water flooding, from the initial stage of water flooding, the water content <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mo stretchy="false">(</m:mo> <m:msub> <m:mrow> <m:mi>f</m:mi> </m:mrow> <m:mrow> <m:mtext>w</m:mtext> </m:mrow> </m:msub> <m:mo stretchy="false">)</m:mo> </m:math> ({f}_{\text{w}}) at the producing end tends to rise more slowly than that at the producing end of water flooding, the final recovery rate ( E R,final ) is the highest, 42.5%, the residual oil saturation is only 33.9%. The decrease in P max and the increase in E R,final indicate that the injection of VR solution can improve the percolation capacity of crude oil, and the method of reducing thin oil viscosity can be applied to the development of special permeable thin oil fields.