Study On Chelate Acidification Mechanism And Influence Factors Of Long 4+5 Reservoir In Liu Maoyuan Block

The block length 4+5 reservoir block in Liumaoyuan is a micro-throat reservoir with low porosity as the main feature.The reservoir belongs to extra-low permeability reservoir.The reservoir has high clay mineral content and strong vertical and horizontal non-average values.Due to the disadvantages of conventional acid acidification,the application of Liumao yuan4+5 reservoirs is limited,so that the effect of acidification and deblocking is greatly reduced,which has a serious impact on the development of the oil field.The chelated acid has a sourite reaction.The advantages of slower rate,longer acid etching distance,no secondary precipitation and the like have a tendency to replace the conventional soil acid in this block,so it is urgent to study the chelating acid acidification mechanism and influencing factors,and provide theoretical support for the optimization of on-site process..This article first analyzes the lithology and physical characteristics of Chang 4+5 reservoirs in Liu mao yuan block,combines the lithology,physical properties,and fluid characteristics of reservoirs to analyze the causes of damage caused by acidification of conventional soil acid and the resulting damage;Acid composition,through the comparison of the dissolution rates of different samples at different temperatures at the same temperature of chelating acid and soil acid,and the dissolution rates of different samples at different concentrations of chelating acid,to study the effects of chelating acid on fluorine at different pH and temperature.Precipitation of the compounds and inhibition of hydroxide precipitation,study of the mechanism of chelating acid acidification,and study of the compatibility of chelating acid and injected water,analysis of the cause of reservoir blockage,the dissolubility of core powder at different concentrations of chelating acid,and different time The dissociation rate of the core powder was compared with that of the acid solution.The acid injection concentration and the CT scan of the core before and after the acid injection were used to observe the change of the pore and throat through the core displacement experiment.Finally,according to the reservoir characteristics and chelating acidacidification mechanism and acidification factors,the acidizing construction process?including the amount of chelating acid injected,acid injection speed,etc.?was designed.Research indicates:?1?The 4+5 reservoirs in the Liumao yuan block are mainly composed of intergranular pores.The pore combination types are mainly intergranular pores,intergranular pores and dissolved pores,and the pore throat distribution has strong heterogeneity.The porosity is11.54%,the average permeability is 1 to 0.1×10^-3?m 2,and the average pore size is 35?m,belonging to the low pore-to-tertiary low permeability reservoir.?2?The interstitials in the Chang 4+5 reservoirs include kaolinite and illite,the filling method of interstitial materials,the intrusion of foreign solid particles,and the attachment of clay minerals to the pore wall,resulting in acidification of the soil for various reasons.Can cause reservoir blockage.?3?The dissolution rates of bentonite by the soil acid and the chelating acid are basically the same at different times;in the three samples,kaolin,bentonite and sand,the acid and chelating acid have the highest dissolution rate to bentonite.The corrosion rate of kaolin is the lowest;the dissolution rate of chelating acid to kaolin and sand is basically higher than that of soil acid;the dissolution rate of soil acid to the core powder is higher than that of chelating acid,and the dissolution rate of soil acid decreases afterwards.The dissolution rate of acid is higher than that of soil acid and tends to be stable.?4?The inhibitory rate of chelating acid on the precipitation of magnesium fluoride gradually decreased with the increase of ph of the reaction solution;the inhibition of calcium fluoride precipitation and precipitation of Fe?OH?₃ with chelating acid did not change greatly with temperature,calcium fluoride precipitated.The inhibition rate is about 55%-66%,and the ferric hydroxide is about 50%-60%.?5?As the acid injection proceeds,the permeability gradually increases from the beginning of the decrease,even beyond the original initial permeability.Under the same injection volume,the acidification effect of 1:1 acid concentration was significantly better than that of 2:1 and 1:2.It is recommended to acidify the acid at the site:water=1:1.From the core CT scan before and after acid injection,it can be seen that pores and throats after acid injection become larger than those before acid injection.After injection of acid,the inlet pores and throat are larger than the outlet pores and throat radius.?6?Water injection volume for block 4+5 is 15-20m³ per day for single wells,with an acid content of approximately 10.3m³,acid injection time of 14.7h,on-site acidification according to acid:water 1:1,acid displacement 0.6-0.8 m³/h.