Research And Application On Starch Graft Acrylamide Polymer Gel System

With the development of polymer chemistry,polymer materials were widely used in various fields of petroleum industry.Based on the reaction between polymer and crosslinker,the polymer can form a high strength gel plug which can resist high pressure and temperature in the wellbore.After operation is complete,the gel can be broken into fluid with gel breaker.All these ideal properities make polymer gel play an irreplaceable role in water shutoff,profile control,workover and plugging operation.According to the difference between crosslinkers,the polymer gel system can be divided into organic polymer system and inorganic system.Cr?III?/HPAM gel system was the first one to be developed and widely used polymer system.However,this gel system has some shortcomings such as short crosslink time and low gel strength,because the complex bond between polymer and crosslink is weak which limit the application of gels in high temperature wells.Organic gel systems,such as phenolic resin/HPAM,PEI/HPAM gel system,are based on the covalent bond from the chemical reaction between polymer and organic crosslinkers.This feature makes the gel can resist high temperature and high pressure.But the high strength property also makes it difficult for gel to be broken into fluid after the field operation.By optimizing reaction conditions for starch graft copolymerization of AM by changing stirring rate of reaction vessel,reaction temperature,reaction time,reaction system pH value,iniator dosage,reactang total concention and every reactant concentration so on,this research used solube starch and acrylamide as reactant and ceric ammonium nitrate as iniator and synesised a polymer gel with natural polymer starch as the skeleton and graft ratio up to 88.2%.Using the phenolic resin as crosslinker makes the gel has high strength and high temperature resistance properties.The gel can be easily broken into fluid after using gel breaker because the gel skeleton is macromolecular starch.Through core damage test,it was found that the damage rate of gel to core can be reduced to about 10%after gel breaker treatment.The gelation time can be adjusted from 1⁷h at 100?by changing crosslink ratio,and the gel can resist high temperature up to 160?without being hydrated or broken.The gel has excellent acid and alkali resistance and also perform well in the condition with oil or acid gas?CO₂,H₂S?.The stability test showed that the gel remained stable in 10d at 120?.When adding 20%gel brake agent after the gel formed,the gel can be totally broken into fluid within 8h,and the apparent viscosity of the gel breaking liquid is about 16mPa·s.And the damage rate of the reservoir treated by gel breaker can be reduced to about 10%in 8d.The gel system in this paper was successfully applied in ANZZ-13well located in North Azadegan field.During the workover operation,injected 80m gel plug in the well depth 2780m,finally through pressure test,the gel resisted pressure to 1400Psi,the test result shown that the gel was stable in the wellbore.Compared with the former cementing plug operation by implementing the polymer gel plug,the success rate of the cementing plug operation is improved,and the risk of the workover fluid and other fluid contaminated reservoirs is reduced because of the separation of the reservoir and the well section,and the construction cost is also saved.