| In-depth profile control technology using pre-gelled particles as profile controlagent has been developed rapidly in recent years. It is a new technique to better themacroscopic sweep efficiency and enhance oil recovery. It has gradually become theresearch focus worldwide because it can overcome the main drawbacks of in-situgelation system, such as ungelation or degraded gel strength due to shear,degradation, dilution, pH change, asynchronous absorption between the crosslinkerand polymer.Starch grafted-poly (AM/SSS/DAC) copolymer, used as profile control agent,was prepared by graft copolymerization among starch, acrylamide (AM), sodium4-styrenesulfonate (SSS) and acryloyloxyethyltrimethlammonium chloride (DAC) inaqueous water solution, using ammonium persulfate and sodium bisulfite as redoxinitiators and N, N’-methylenebisacrylamide (NMA) as crosslinker. Factorsinfluencing water absorption rate, gel strength, shear-resistance andthermo-resistance of the starch graft copolymer profile control agent, such ascrosslinker amount and SSS amount，together with the effect of DAC amount on thewater absorbency and salt absorbency of the starch graft copolymer profile controlagent, were investigated. Morphologies and structure of the starch graft copolymerprofile control agent were characterized by way of FTIR, SEM and X-ray diffraction(XRD), respectively. The starch graft copolymer profile control agent showedsuitable water absorbency, water absorption rate, controlled swell ratio, and good gelstrength and shear-resistance and thermo-resistance. The main research results areas follows:(1) The optimal technological conditions to preparation the starch grafted-poly (AM/SSS/DAC) copolymer are as follows:12wt%starch (based on the totalmonomer mass),5wt%AM(based on water mass),20wt%SSS(based on AM mass),15%DAC(based on AM mass),0.2wt%NMA(based on the total monomer mass)and0.8wt%ammonium persulfate (based on the total monomer mass).(2) The starch grafted-poly (AM/SSS/DAC) copolymer can reach waterabsorption equilibrium within350min with equilibrium absorbency of120g/g, whichindicates that the starch grafted-poly (AM/SSS/DAC) copolymer meets therequirements of suitable water absorbency, water absorption rate and controlledswell ratio for profile control.(3) Water absorbency of the starch grafted-poly (AM/SSS/DAC) copolymerdecreased with increasing SSS amount up to10wt%, beyond which waterabsorbency increased with increasing SSS amount. The gel strength, shear-resistanceand thermo-resistance increased with increasing SSS amount in the starch grafted-poly (AM/SSS/DAC) copolymer.(4) Water absorbency decreased, and gel strength, shear-resistance andthermo-resistance increased with increasing crosslinker amount in the starch grafted-poly (AM/SSS/DAC) copolymer.(5) SEM data showed that spherical and oval starch particles disappeared andporous gel aggregates with many microporous holes of different sizes were formedafter starch graft modification.(6) FTIR demonstrated preliminarily the structure of starch grafted-poly(AM/SSS/DAC) copolymer. XRD result indicated that there existed the graftreaction between the starch and monomers, which destroyed the crystalline structureof starch. The prepared starch grafted-poly (AM/SSS/DAC) copolymer had anamorphous structure.(7) TGA and DSC curves of the starch grafted-poly (AM/SSS/DAC) copolymercan be divided into three stages with the good thermo-stability of the starch grafted-poly (AM/SSS/DAC) copolymer higher than220℃. |
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