Study On The Influence Of Heterogeneity On The Change Rule Of Liquid Production Capacity In Sandstone Reservoir

Extract is one of the main measures for stable production of sandstone water injection development reservoirs at high water cut stage.Whether the well can achieve a certain liquid production capacity is a prerequisite for achieving lextraction.The dimensionless fluid productivity index of sandstone reservoir is an important index to measure the change of liquid production capacity of waterflooded reservoir.The dimensionless fluid productivity index curve is usually used to characterize the change law of liquid production capacity.Dimensionless fluid productivity index can be calculated by theoretical method and field method.Practice has proved that the two calculation methods are basically same when the oil well fails to reach high water cut,but there are great differences in the later stage of high water cut.In view of this problem,using the reservoir numerical simulation method,the reservoir seepage field and development index of different physical property,different heterogeneity degree and different injection production well working system are simulated,and the difference of the dimensionless recovery index curve obtained by the theoretical method and the field method is compared and analyzed.The main progress achieved is as follows:(1)Based on the experimental test method of oil-water relative permeability,the deficiency in the calculation method of theoretical dimensionless fluid productivity index was analyzed and studied,which mainly includes two points:firstly,the core size is too small to truly reflect the heterogeneity in the actual reservoir;secondly,the flow pattern in the core experiment is one-dimensional linear flow and cannot truly simulate the complicated flow state of fluid in the actual formation.Through the numerical simulation of core displacement,the influence of the characteristic value of the phase permeability curve on the change of the theoretical dimensionless fluid productivity index curve was analyzed.The results show that,the theoretical dimensionless liquid productivity index reflects the change degree of the fluid production capacity of water flooding in the core,and the relative permeability curves can reflect the change law of dimensionless liquid productivity index curve to a certain extent.(2)Through the numerical simulation method,a quarter injection-production unit of a five-point injection-production well pattern is simulated under constant pressure difference working system,and the influences of the permeability anisotropy,oil-water viscosity ratio,heterogeneity of permeability and different working systems on the change of dimensionless fluid productivity index curve of the field are studied.The results show that,the influence of heterogeneity on the dimensionless fluid production index of field is very small under the constant pressure differential working system,and the dimensionless fluid productivity index simulated under the working system of injection with constant quantify and production with constant pressure is consistent with the dimensionless fluid productivity index of the actual sandstone reservoir.(3)Different heterogeneity parameters are set in the numerical simulation mechanism model to study the influence of heterogeneity of sandstone reservoir on the variation law of dimensionless fluid productivity index curve of the field.Then,the correlation analysis method in grey system theory is used to obtain the influence degree of various heterogeneous parameters on the change of dimensionless fluid productivity index curve of the field.The results show that the heterogeneity affects the distribution of oil and water,thus affecting the dimensionless fluid productivity index curve of the field.The width of the hypertonic zone,that is,the heterogeneity parameters of the dominant channel,make more oil cannot be displaced by water,which has the greatest influence on the change of dimensionless fluid productivity index curve of the field.(4)By analyzing the difference between theoretical dimensionless liquid production index curve and the dimensionless fluid productivity index curve of the field,the reason for the difference is analyzed and the calculation method of dimensionless fluid productivity index is corrected.The results show that,in the calculation method of the dimensionless fluid productivity index of the field,the current oil and water production is equivalent to the multiple of the initial production(only crude oil),and the pressure changes were not taken into account.Meanwhile,the heterogeneity will affect the pressure change.To make the theoretical dimensionless liquid production index curve conform to the dimensionless fluid productivity index of the field,the original formula for calculating the dimensionless fluid productivity index of the field should be divided by injection-production pressure difference to carry out correction.