Synthesis And Performance Evaluation Of Amphoteric Starch Graft Copolymer Drilling Fluid

As a natural macromolecule, starch has many advantage, the resource is very plenty, price is cheap, non-poisonous, bio-degradable and can be modified easily. So that, with more and more appreciating of regenerative resources and environmental friendly chemical industry, the modified starch is more and more be appreciated by people. Modified starch has been using a long time as drilling fluid additives, but the low resistance of temperature still limits it’s range of application. The method of starch’s modify is such as esterfying, etherifying, grafting, oxidizing, cross-linking.To increase the low resistance of temperature and other capability, this text adopt a method of graft copolymerization to grafting DMDAAC、AMPS、AM to starch in the condition of ammonium peroxydisulfate as initiator. By way of one-way factor analysis experiment, analyzing reaction conditions such as temperature, time, dosage of initiator, monomer proportion, pH to affect the percent grafting, grafting efficiency and monomer conversion rate, and the result of the experiment indicate that percent grafting, grafting efficiency is go up first and then reduce by the temperature, time, dosage of initiator, monomer proportion, pH’s changing of the experiment. The best temperature is 60℃, best time is 4hours, best dosage of initiator is 0.5%, best pH is 8, best proportion of starch and monomer is 1:4, best proportion of DMDAAC and AMPS is 1:3, and analysed the construction of the polymer by infra-red spectrum(IR), and scanning electron microscopy (SEM),the IR result prove that the polymer is the aim production and the SEM photograph showed that the surface of the grated-starch is changed.Evaluating each performance of the drilling fluid which added polymer composited in this text, the result show that 1% dosage of the modified starch can resist saturate salt water, can be still used in 5% calcium’s drilling fluid,0.6% dosage of the polymer can raise the resist temperature to 180℃,and the filtration loss is only 10.8mL, the drilling fluid which added 0.6% modified starch in 150℃and 3.5mPa it’s filtration loss is 24.2mL. The first and the second percent recovery of Shale trundle recycling is greater than 90%. All this show that the modified starch is good in filtration properties, temperature resist and shale anti-caving. Compared the modified starch with other drilling fluid additives which used usually in filtration loss, the result indicate the modified starch in better than other drilling fluid additives.