The Calculating Method Of Relative Permeability Curve For Correcting End Effect In Tight Core

The relative permealility curve is the important basic data for studying oil-water two-phase seepage.The tight sandstone reservoir has small throat and large capillary force.So the end effect of the core is significant,causing the water phase at the end of the core to stay and the water saturation to rise,which causes the measured relative permeability curve to deviate from the true curve.Therefore,studying the effect of correcting the end effect,it is proposed that the new relative permealility curve calculation method is of great significance for the production and development of tight reservoirs.This paper is based on the mechanism of the end effect and the characteristics of the traditional measurement method it didn’t consider the capillary to cause the calculation error of the relative permeability curve.Adopting the method of establishing one-dimensional twophase numerical simulation model considering the influence of end effect.Proposing the iterative method for correcting the relative permeability curve in the steady-state method and the correction plate method for correcting relative permeability curve in the unsteady-state method are proposed.The sensitivity degree of the influencing factors of relative permeability curve was proposed,and the dimensionless parameters were proposed.The fitting formulas corresponding to the morphology of the tight core phase infiltration curve were screened,and the relationship between the experimental relative permeability curve and the reservoir relative permeability curve was constructed.the correction of the influence of end effect in tight cores was completed and an example calculation was performed.At the same time,the degree of influence of the end effect on the relative permeability curve in different laboratory core measurement methods was compared.The results show that the end effect caused the water saturation of the measured core to be high,which affects the accuracy of the relative permeability curve.In the steady state method,reducing the oil-water ratio injected,or increasing the injection flow rate or increasing the core length can effectively reduce the test error caused by the end effect.In the non-steady-state method,increasing the displacement pressure difference or increasing the core length can effectively reduce the test error caused by the end effect.But there is a limit to the reduction.At the same time,only changing the experimental conditions can not completely eliminate the test error caused by the JBN calculation method.And the influence of the end effect in the steady state method is smaller than that of the non-steady state.the error between the experimental relative permeability curve and the reservoir relative permeability curve the tight core is generally less than 1% in the steady state method,The error in the unsteady state method is generally more than 5%,mostly around 10%.