| Because of the delay of releasing,the encapsulated gel breaker was used to ensure the viscosity of fracturing fluid and enhance the practical concentration of encapsulated gel breaker within the fracturing process.So the natural gel and synthetic polymer gel fracturing fluid could be fully broken and the reflux cleared out the residue which contributed to keeping the flowing capability of the support layer and lessening the impact on the reservoir.Because of a series of problems in the preparation of the gel capsule breaker,such as uneven coating,uncontrolled releasing delay and high cost,encapsulated gel breaker could not widely applied easily.Studying on the way and process of coating on the potassium persulfate and ammonium persulfate had pragmatic significance for the capsule breaker of the water-based fracturing fluid.The coating way and process of potassium persulfate were explored with the solution method on the base of the natural polymer gelatin acted as coat,liquid paraffin played as oil phase,span80 used as stabilizer,and formaldehyde served as crosslinking agent.The system was considered as oil coated in solid(O/S).With the orthogonal test,it could be shown that the optimum conditions of the coating process were followed as:the mass ratio of the core and the wall was 4:5,the volume ratio of water and the oil was 1:5,the mass concentration of stabilizer was 1.5%,the stirring speed was 400r/min,the volume of formaldehyde was 1.75ml,the mass concentration of the coating solution was 15%.Moreover,the coating method and process of ammonium persulfate were studied either on the condition that ethyl cellulose(EC)acted as coat,gelatin played as protective addictive,ethylene chloride used as organic solvent.The system was regarded as solid coated in oil and oil coated in water(S/O/W).And the optimized coating process was followed as:the mass ratio of the core and the wall was 1:4,the volume ratio of water and the oil was 1:4.5,the mass concentration of EC was 5%,the stirring speed was 225r/min,the mass concentration of gelatin was 1.75%.The morphology of the optimized capsule breaker was observed by optical microscope and SEM,which was much better than that of the raw.The sphericity of the capsule breaker coated with natural polymer gelatin was more than 0.9 and the diameter of that ranged from 450μm to 700μm.However,the diameter of the sample coated with EC were 450～650μm.EDS and FTIR proved that the gelatin was able to coating potassium persulfate well and EC could coated on the ammonium persulfate perfectly.The thermal stability of the samples analysized by TG,potassium persulfate capsule lost 33.40%weight at 550℃ and the ammonium persulfate capsule only lost 68.45%weight at 450℃.The electronic conductivity was carried by soaking the capsule breaker in the pure water,and the releasing property of the sample in varied temperature was explored.The results showed that the releasing rule of potassium persulfate capsule conformed to the zero kinetics rule(R=25.35+0.974t)at 60℃ in 1 hour and under atmospheric pressure,and that anmonium persulfate capsule did not release under the pressure,but the releasing mass fraction of the sample was 42.66%at 60aC in 1 hour after the sample crushed.When these two capsule breakers were used in the guar fracturing gel,the gel-broken rules were shown that the potassium persulfate capsule could break the gel of 60℃ within 2 to 3 hours while its mass concentration was 0.03%,and the residue amount of the gel-broken liquid was 0.162mg/mL,but the viscosity retention of the fracturing gel was 48.42%in 1 hour,and that ammonium persulfate capsule was suited to break the fracturing gel of 80℃ within 3 hours when its dosage was 0.05%,and the residue amount of the gel-broken liquid was 0.147mg/mL,but the viscosity retention of the fracturing gel was 58.95%within 1 hour.Finally,for the production capacity of 1 ton of these two capsule breakers,the economic efficiency was evaluated and had good profitability. |
PDF Full Text Request