| Nowadays, low permeability reservoirs take a great amount among domestic onshore oilfields, and with a mass of water breakthrough, just using mechanical water shut off can’t meet the demands, so the chemical method and new shut-off agent are essential, the study on water shut-off agent has a practical significance for higher recovery and economic benefit.Acrylic acid/acrylamide copolymer was synthesized by instantaneous polymerization, during the process, acrylic acid and acrylamide(AA/AM) as main raw materials, anhydrous sodium sulfite-potassium persulfate(Na2SO3/K2S2O8) as the initiator system. The effects of different reaction conditions had been studied in detail. The results showed that molecular weight was decreasing with the increasing dosage and the ratio of initiator, but for solid content, on the contrary, when beyond the some point, water solubility dropped. On the other side, when the monomer ratio changed, the molecular weight decreased firstly, then increased and the consequences of solid content and water solubility were in opposite of molecular weight. By comprehensive analysis, the suitable synthesis conditions were obtained:dosage of initiator was1.0%wt, the ratio of initiator was0.8, the monomer ratio was1:1.2at26℃, in the situation, intrinsic viscosity was1.2X103mL/g, viscosity molecular weight was8.3X104. FT-IR were used for confirming the existence of hydroxyl group with stretching vibration absorption at3448cm-1, as well as asymmetric stretching vibration absorption of acylamino group at1652cm-1.Gel shut-off agent was obtained from AA-AM copolymer reacting with HMT and phenyl acetate. The befitting condition to synthesize gel shut-off agent which was got by orthogonal test at30℃during24h in formation water was:the concentration of copolymer, HMT, phenyl acetate at9%wt,0.7%wt,0.6%wt separately. Dosage of copolymer had a great effect on water absorption, the water absorption was37.01g/g in better formula, gel strength had been influenced by the phenyl acetate, the gel strength was in F-J in an extended period at80℃, foreign Marathon gel strength code and domestic gel strength code were discussed. The basic properties and main application performances had been discussed deeper. The results showed: at80℃, water absorption of gel almost grew straight, and the water absorption was74.55g/g in24h. when gel was in distilled water or formation water or NaCl solution at30℃during48h, water absorption of the gel were98.94g/g、23.87g、19.14g/g, however, in CaCl2solution the property just was2.42g/g. When gel was in formation water at80℃, water absorption changed with the storage time, in the first day, the water absorption got to63.80g/g, it was gradually stable after three days to85.26g/g. And when gel was in light oil at the same temperature, shrinkage was bigger during the first four days at30.84%, after that the changes were not obvious. SEM and TG were used for studying the gel microstructure and thermal stability severally, and from these results, the gel had some holes and through-holes, and the beginning temperature of weight loss was89℃. The coreflooding experiment was carried out. the shut off rate was81.95%in the low permeability core. According to these results, the water absorption of gel in formation water with hypersalinity and injection in low permeabili-ty formation should be ameliorated for better shut-off effect. |
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