| The TB block in Xingnan oilfield is a typical extra low permeability sandstone reservoir,it has many characters,such as low porosity and permeability,severe heterogeneity and strong reservoir sensitivity.During the waterflood development,many problems have appeared,such as the rapidly-increasing pressure in injecting wells and the rapidly-decreasing pressure in producing wells,the traditional measures have various defects in low permeability reservoir,such as the validity of acidification,fracturing is relatively short and they may induce formation damage.The indoor and field practice have proved that the application of surfactant in the low permeability reservoir can reduce the injection pressure and increase water injection dramaticlly.Therefore,to improve the displacement effects in reservoir and enhance oil recovery,it is necessary to carry out the research of decreasing injection pressure and increasing injection rate by surfactant in xingnan oilfield.In this paper,based on the reservoir physical property of low permeability reservoirs in the TB block of Xingnan oilfield,by measuring the interfacial tension and other measures,the applied concentration of petroleum sulfonate was optimized,which is the main agent.In order to improve the effect of decreasing injection pressure and increasing injection,the surface active agent were screened in 35 kinds of surfactants,which is compounded with the main agent,and the additives were also be screened,finally,the surfactant formula used for decreasing injection pressure and increasing injection rate in the Xingnan oilfield was developed,the stability and compatibility of the formula were evaluated.By means of indoor natural core displacement experiment,the decreasing injection pressure and increasing injection rate simulation experiment of surfactant flooding was carried out,the effect of surfactant formular were proved,and systematically studied the influence law of the injection concentration,the injection volume,the injection speed,the surfactant slug size and the combination of surfactant slug in the natural low permeability core simulation experiment,and the the ratio of decreasing injecting pressure of surfactant fomular were measured.As the results,the surfactant formula used for decreasing injection pressure and increasing injection rate in the in the Xingnan oilfield was:1.5%WC-1+0.9%6501+0.5%YC-1+0.3%ZS-2+0.5%Na Cl,the optimum injection concentration is 0.5%,the volume ratio is 1:1:1:1:1,and the interfacial tension with the crude oil is 8.61×10-3m N/m;the best injection volume is 0.5PV,the best combination of surfactant slug is 0.25PV+0.15PV+0.10 PV,the period of validity of the formular is 17.67 PV.In the condition of best injection parameters,the ratio of decreasing injecting pressure of surfactant fomular is 18.73%.In TB block of Xingnan oilfield,the surfactant formular were applied in 8 wells,the results show that the average single well water injection rate increased from 18m3 to 28m3,increased 10m3,the average single well injection pressure decreased from 14.2MPa to13.1MPa,decreased 1.1MPa,field test achieved good effect of decreasing injection pressure and increasing injection rate. |
