| Water injection is one of the most commonly used development methods for low-permeability reservoirs.However,long-term water injection development would cause reservoir blockage,resulted in a gradual increase of pressure in the injection wells,resulted in a decrease in energy efficiency or even a low injection,which would lead to a decrease in oil recovery.In response to this problem,it is generally solved by matrix acidification and plugging of surfactant for depressurization and injection.The advantage of acidification is that it has a quick effect,but long-term effect is poor,and the effect of surfactant depressurization is slightly weak,but it can maintain the effect for a long time,and there are few reports on the combination of the two methods.Therefore,based on the problem of pressurized and unfilled injection of low-pore-low-permeability Chang 3 reservoir injection wells in ELHZ block of Longdong Oilfield,this paper carried out research on the acidification-surfactant combination pressure reduction and injection injection technology of high pressure water injection wells.The measurements indicate the permeability average value of the reservoir is 4.52×10-3?m2and the average porosity is 11.46%,which is a low permeability reservoir.The statistical results of core permeability indicate that the reservoir has a moderately weak anisotropism.The production data shows that permeability of 89.70%of the wells below 10×10-3?m2,and25 of the 165 wells are under injection.The above results indicate that low-permeability reservoirs are susceptible to unbalanced water injection and cause partial wells to be under injection.There are three reasons for the serious shortage of some wells in the area:one is that the reservoir has low permeability and porosity;the other is that the clay particles in the reservoir are damaged or treated after acidification,causing secondary damage,which leads to blockage of the formation,the third is that the water injection water is not compatible with the formation water,and after mixing,the calcium carbonate scale is blocked to block the formation,which is the main factor causing the water injection to decrease.Based on the results of the analysis of the cause of under-injection,the methods of acid-pressure deblocking and surfactant combination depressurization and injection were studied.Firstly,the multi-hydrogen multi-hydrogen acid XS-1 was obtained through drug screening and formulation optimization.The acidification experimental results show that XS-1has good dissolution and retardance properties,which can effectively improve the permeability to 4.15 times after injection,and no secondary precipitation occurs.The kinetic equation of XS-1 acid and rock was obtained by the acid rock reaction model and the core flow experiment was-rR=1.23586×10-4·C0.83102.The reaction rate constant was smaller than that of the conventional acid solution,indicating that the acid solution can be effectively increased reaction time and distance.Secondly,the research also obtained a surface active compounding system XS-2A,which has good compatibility with the injected fluid,can reduce the oil-water interfacial tension to 3.11×10-3 mN/m,and has good wettability reversal.The water injection pressure was reduced by about 50.70%,and the oil displacement efficiency is up to 42.18%,showing excellent depressurization and injection performance.Finally,using the acid-surfactant compounding system synergistic effect technology,on-site test was carried out on the oilfield for two acid-stained serious injection wells.The results show that the water injection volume of ZG77-67 and ZG73-55 has been significantly improved,reaching the requirements of the daily injection volume,and the water injection pressure is reduced respectively by 1.2 MPa and 3.5 MPa. |
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