Study On Large-Scale Physical Simulation Experiment Of Water-Flooding Remaining Oil Distribution In The Extra-High Water Cut Stage Of GT Reservoir

GT reservoir is located in the Central Saertu Oilfiled,having been put into production since 1981.After more than 30 years of water flooding development and several major well pattern adjustments,the total composite water cut is as high as 95%at present.The heterogeneity of the reservoir is very serious,futhermore,the long-term ordinary water flooding development aggravates the degree of reservoir heterogeneity,causing the contradiction of plane,inter-layer and intra-layer to be evenn more serious.The water flooding efficiency in the extra-high water cut stage has become very low,and the distribution of remaining oil has become more complicated.However,as far as current technical conditions and economic benefits are concerned,water flooding mode is still one of the main development means of the oilfield.So in order to enhance the recovery of the extra high water cut stage oilfield,we should further understand the distribution characteristics of remaining oil in extra-high water cut stage,make the mechanism of water flooding in ultra-high water cut stage clear,analyse and predict the EOR effect of different water drive measures,thereby providing a theoretical basis for the development and adjustment of water flooding in the extra-high water cut stage oilfield.Physical simulation technology in laboratory is an effective method to simulate the process of oil displacement and study oil displacement mechanism.However,the conventional one-dimensional and two-dimensional models have poor effect on the simulation of heterogeneous reservoirs in extra-high water cut stage.In this paper,three-dimensional physical model,which has larger scale and more accurate experimental results,is used to study the mechanism of water flooding and the distribution characteristics of remaining oil in extra-high water cut stage well.According to the basic geological characteristics of the reservoir,the prototype parameters of the reservoir are transformed into three-dimensional physical model parameters by the similarity principle and the derivation of similarity criteria.Thus large-scale three-dimensional physical electrode models have been developed and applied to water flooding experiments in this paper,meanwhile,the resistivity measurement method based on Archie's formula is improved to determine the distribution of remaining oil saturation,a more suitable method for calculating large-scale model electric sweep efficiency is proposed and adopted.The remaining oil distribution and the mechanism of water flooding in extra-high water cut stage can be better analyzed by combing the results of resistivity measurement data and experimental data of water flooding.In this paper,four kinds of large-scale model experiments of water flooding are designed and carried out,including plane homogeneity,plane heterogeneity,intra-layer heterogeneity and inter-layer heterogeneity.By establishing oil-water distribution and taking different water flooding stimulation measures in extra-high water cut stage,the effects of heterogeneity,permeability,initial displacement velocity,timing of speed-up and water injection mode on water flooding recovery degree are mainly studied,as well as the improvement of recovery efficiency of different heterogeneous models at the later period of extra-high water cut stage by later-period measures,such as increasing water injection rate,well pattern adjustment,water shutoff and soaking wells,are also studied.Also,the accurate dynamic distribution data of oil saturation are obtained by correcting the resistivity data with the experimental data,which can be used to study the effect of stimulation measures on remaining oil distribution and oil displacement mechanism in the later stage of water flooding with different heterogeneous models in extra-high water cut stage.The experimental results show that the heterogeneity and permeability are the main factors affecting the recovery efficiency and the distribution of remaining oil in the extra-high water cut stage.The remaining oil is enriched in the area far away from the injection-production mainstream line and the injection well,where the injection water is difficult to sweep,and the heterogeneity will reduce the oil displacement efficiency in the relatively low permeability area,causing the oil saturation to be higher.But taking appropriate later recovery schemes for different heterogeneous conditions can further improve the recovery ratio of water flooding.Finally,some experimental conclusions can be transformed back into reservoir prototype,thereupon some reasonable suggestions for the development of extra-high water cut period can be put forward.