Research On The Technologies For Removing Barium/strontium Sulfate Scale

With most domestic oilfields entering the water injection production stage,the scaling of barium,strontium,and calcium sulfate seriously affects the normal production of oil and gas fields.Well bore scaling results in a drastic reduction of the effective oil and gas passage in the well bore,which affects the production of oil and gas wells.Strontium sulfate deposits in the reservoir can lead to serious reservoir damage,resulting in a sharp decline in oil and gas well productivity.At the same time,fouling of production lines and equipment is associated with or exacerbates equipment corrosion.Firstly,this paper investigates the field conditions of oilfields with severe sulpHate fouling in the country,and combines the site conditions of BZ34-2/4 oilfields.The mechanism,causes and influencing factors of sulpHate scaling in sulpHides are analyzed and studied in detail.The main controlling factor for the determination of the sulpHate scale in this oil field is that the injected water is incompatible with the formation water.The original formation water in the oil field is rich in scale cations such as Ca²⁺,Ba²⁺,Mg²⁺,and Na⁺ions,and scale anions such as HCO^3-,CO^3-,and SO₄^2-.The total salinity is 7100 to 14000 mg/l and the highest is 96,000 mg/l.For NaHCO₃ water type,the total salinity of the injected water is above 30,000 ml/l,and the contents of Ca²⁺,Mg²⁺,and SO₄^2-are significantly higher than those in the original formation water.Among them,the SO₄^2-content is basically above 1700 mg/l and up to2400mg/l or so.The HCO^3-and CO₃^2-content are relatively low compared to the original formation water.The injected water belongs to the NaSO₄ water type.Mixing both produces large amounts of sulfate and carbonate scale.Based on the analysis of the mechanism of fouling,the additives such as chelating agents,chelating auxiliaries and corrosion inhibitors were optimized,and a scale cleaning agent with high scavenging capacity and fast cleaning speed against cesium sulfate insoluble scale was developed.Through a large number of laboratory tests,it can be seen that EDTA,DTPA,macrocyclic crown ethers,and several glucose modified products have excellent chelating ability for barium sulfate,especially a large ring crown with a certain special structure.Ethers,such as cryptoxins[2,2,2].However,due to its relatively expensive price,if it is the main chelating agent as a scale remover,the cost is too high.On the other hand,although DTPA and EDTA are relatively weak in the solubility of barium sulfate,the cost is much lower than that of cryptoether[2,2,2].Therefore,DTPA and EDTA are the main chelating agent components in the compounding process.The scaling rate of the scale cleaning agent developed in this paper reaches more than 80%,and the performance is stable.In addition,detailed researches have been conducted on the scaling rate,temperature resistance,acidity and alkalinity of the scale-cleaning agent and the compatibility of the formation fluid,and the system formulation suitable for BZ34 oilfield has been obtained.The formula of the scale-cleaning agent system is:EDTA0.2mol/l+DTPA0.2 mol/l+oxalic acid 0.2 mol/l+potassium fluoride 0.1mol/l+PBTCA 3%.On the other hand,the core flooding experiment was used to simulate the formation process of the sulpHate scale in the reservoir,and the effect of scaling on reservoir damage was analyzed.On this basis,combined with the above developed scale remover for core plugging experiments.Based on the above conclusions,the process of removing barium sulfate from the wellbore and the reservoir is discussed.