Preparation And Properties Of Starch Grafted-Poly(AM/SSS/DAC) Fluid Loss Reducer

Starch is a rich source of biomass and can be given some new characteristics bythe graft copolymerization method due to its hydroxyl groups. It has become one ofthe important oil field chemicals, which has been widely used in petroleumexploration and development because of its low price, abundant resource andbiodegradable properties. As a drilling fluid additive, it can be used as saturated brinedrilling fluid filtrate reducer because of its strong salt resistance. However starch’sdrawback is the poor resistance to temperature, Starch grafted copolymer maintainsthe good salt-resistance of starch and enhances the temperature—resistance of starch.Therefore starch grafted copolymer has gradually gained much attention of the oilfield chemical workers.Starch grafted-poly (AM/SSS/DAC) copolymer used as fluid loss reducer wasprepared by water solution graft copolymerization among starch, acrylamide (AM),acrylyloxy ethyl trimethlammonium chloride (DAC) and sodium styrene sulfonate(SSS) in aqueous solution, using ammonium persulfate and sodium bisulfite as redoxinitiators. Factors influencing the graft efficiency of the graft copolymers, such as Amcontent, SSS amount, temperature and initiator amount, and the apparent viscosity ofthe starch grafted copolymer solution, such as initiator amount, SSS amount andtemperature, etc, were investigated. Effects of starch grafted copolymer concentrationon the reduced viscosity, as well as DAC amount on the performance of the drillingsfluids were also studied. Structure of the starch graft copolymer fluid loss controlagent was characterized by way of FTIR spectrum and X-ray diffraction. TGA andDSC analysis were used to characterize the thermo-stability of the starch graftedcopolymer. The main research results are as follows:(1) Apparent viscosity of the starch grafted-poly (AM/SSS/DAC) copolymerwater solution decreased monotonously with increasing initiator amount, while graft efficiency of starch modification increased with increasing initiator amount up to1.3wt%, beyond which graft efficiency decreased again.(2) Apparent viscosity of the starch grafted-poly (AM/SSS/DAC) copolymerwater solution increased with increasing SSS amount up to15wt%, beyond whichapparent viscosity decreased again.(3) Apparent viscosity of the starch grafted-poly (AM/SSS/DAC) copolymerwater solution decreased with increasing temperature, while the higher thetemperature, the less the decrease in apparent viscosity, indicating goodtemperature-resistance of the starch grafted-poly (AM/SSS/DAC) copolymer.(4) Fluid loss of the saltwater-based mud decreased with increasing DAC amountup to15wt%, beyond which fluid loss increased again.(5) By optimizing the polymerization process,we gained the best polymerizationreaction parameters: the concentration of acrylamide(AM) is12%,the concentration ofstyrene sulfonate(SSS) is15%, the concentration of acrylyloxy trimethyl ammoniumbromide(DAC) is15%,that is,the ratio of SSS、 AM and DAC is4:5:4;theconcentration of initiator is1.3%, this polymerization’s temperature is controlled in64-68℃,finally we achieved the objectives of a stable and rapid polymerization andcopolymers with high molecular weight.(6) FTIR spectrum appears the characteristic absorption peaks which can beascribed to starch, AM unit, SSS, unit and DAC unit, respectively, demonstratingpreliminarily the structure of starch grafted-poly (AM/SSS/DAC) copolymer.(7) XRD result indicated that there existed the graft reaction between the starchand monomers, which destroyed the crystalline structure of starch. The preparedstarch grafted-poly (AM/SSS/DAC) copolymer had an amorphous structure.(8) 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) filtrate reducer higher than265℃.