Synthesis And Performance Evaluation Of Salt-tolerant Fluid Loss Additive For Oil Cement

As one of the most important oil well cement additives,the performance of fluid loss additives(FLAs)is closely linked with the quality of cementing operation.Nowadays,due to the continual decrease of recovery and reserves,oilfield exploration has to develop towards deep well,complex formation and ocean.Offshore cementing engineering is under active exploration and seawater cement slurry has been promoted in recent years,so requirements of FLAs' performance have become increasingly stricter.However,there is little research touching upon the FLA available in seawater cement slurry.To certain extent,for these widely used AMPS-based copolymers,the paradoxical relationship between viscosity and fluid loss limits their application in the offshore area.Meantime,metal ions in the ocean also exert negative effects on the overall application performance of FLAs and cement slurry.Aimed at those problems mentioned above,a new fluid loss additive was synthesized via the method of radical polymerization in aqueous solution with preferred functional monomers and molecular structure design.Considering the application performance in the cement slurry,the quadripolymer was optimized by the monomers of 2-acrylamido-2-methyl-propane sulfonic acid(AMPS),N,N-acrylamide(DMAA),itaconic acid(IA)and novel cationic monomer dimethyl diallyl ammonium chloride(DMDAAC).The copolymer is called ADDI.Moreover,optimum formula and reaction condition were acquired through the investigation of polymerization condition.The ADDI was identified by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy,respectively.The analysis result showed that the quadripolymer was successfully incorporated.Meantime,the characteristic properties of the copolymer were determined by means of gel permeation chromatography.The ADDI was even stale when the temperature reached 320 ?through TG and DSC analysis,exhibiting excellent thermal stability.The overall performance of ADDI in cement slurry was tested.The evaluation result revealed that the copolymer has good fluid loss control ability in saline-water slurry and the API fluid loss can be effectively controlled in certain range of temperature.Besides,the ADDI exhibit great dispersive ability in sea-water cement slurry.When the ADDI was at 3% dosage,the slurry seemed close to Newtonian fluidmodel.Furthermore,fluidity of cement slurry added ADDI was superior to that of G81 L under the same condition.And the copolymer did not present obvious retarding problem and has little negative effect on the development of compressive strength at low-medium temperature.The sea-water cement slurry mainly prepared by ADDI showed low viscosity and weak thixotropy in thickening experiment.What's more,the undesirable phenomenon like “false set” or “abnormal gel” was not observed in the thickening curve.Additionally,the ADDI exhibited good compatibility with retarder PC-H21 L and DRF-200 L and these two retarders are applied at low temperature and high temperature,respectively.It is predictable that the quadripolymer ADDI can be potentially applied to sea-water cement slurry system.