Study On High Temperature And Salt Tolerance Polyacrylamide Plugging Agents

Polyacrylamide(PAM) as a water souble polymer has been widely applied in the filed of the technology of water shut-off and profile control in oil reservoirs all around the world, but for polyacrylamide systems, the commonly used cross-linking agents such as potassium dichromate, aluminum citrate, various chromium salts and some organic cross-linking agents such as phenol formaldehyde, which can not only cause the environment pollution, but also have poor effect on water shut-off and profile control in the high temperature and high salinity oil reservoirs.Based on the above problem, this paper presents the methods of preparing two novel polyacrylamide plugging agents, studies and compares each performance. Polyacrylamide (average molecular3000,000, hydrodysis degree<3.0%) is used as main agent, home-made hexmethylol melamine(HMM) and trimethylol melamine(TMM) as the cross-linking agents,through the nucleophilic reaction of the active amino group in PAM molecular side chain amide group with the hydroxylmethyls of the HMM and TMM molecules respectively, PAM/HMM and PAM/TMM cross-linked polymer gels were prepared, as plugging agents. Effects of the reaction temperature, reaction time, pH value, the ratio of raw materials and different concentrations of various salts on the viscosity of the two plugging agents were discussed and analyzed in experiments, and samples after purification treatment were also charaterized by infrared spectroscopy(FT-IR) and thermo-gravimetric(TG). Besides, some performances of the samples of each experimental group were characterized by testing the solid content and the breakthrough pressure gradient. Finally, some samples got under the better experimental conditions were chosen for gel strength grade evaluation and plugging rate test. Conclusions were got as follows:(1)By testing IR spectras of melamine and home-made hexamethylol melamine (HMM) and trimethylol melamine (TMM), respectively. Through analysis and comparison of the IR spectras, the results show that cross-linkers HMM and TMM were prepared successfully.(2)By using FT-IR and STA409PC/PG thermal gravimetric analyzer to characterize polyacrylamide and the PAM/HMM and PAM/TMM cross-linked products, the results show that cross-linking reaction of the polyacrylamide with hexamethylol melamine or trimethylol melamine occurred. Therefore, the PAM/HMM and PAM/TMM cross-linked polymers were obtained successfully.(3)PAM/HMM gelation systems under different formulations and the experimental conditions were used for viscosity test, the result shows that the PAM/HMM best gelation conditions:polyacrylamide7.10g, hexamethylol melamine3.16g, filter water100mL, reaction temperature100℃, reaction time4.0h, pH5; For PAM/TMM gelation system, the best conditions into a gel:polyacrylamide7.10g, trimethylol melamine3.46g, filter water100mL,reaction temperature100℃, reaction time4.0h, pH5.(4)The optimization experimental groups of PAM/HMM and PAM/TMM gelation systems were applied in different concentrations salt solution system such as crude salt, potassium chloride(KCl), anhydrous calcium chloride (CaCl2) and magnesium chloride(MgCl2), the results of solid content test and breakthrough pressure gradient test for each sample show that when polyacrylamide dosage is7.10g, hexamethylol melamine is3.16g or trimethylol melamine is3.46g, filter water is100mL,reaction temperature is100℃, reaction time is4.0h, pH value is5,the two plugging systems were both applicable to coarse salt concentration range from10to300g/L, and when experiment materials ratio and reaction conditions were fixed, coarse salt concentration is lOg/L, the two plugging systems were both applicable to KCl concentration range from10to300g/L,CaCl2and MgCl2concentration range from10to250g/L.(5)When tap water is15ml, pH value is5, reaction temperature is100℃, the corresponding gel systems were prepared by adjusting to the PAM/HMM or PAM/TMM ratio, and samples of each experimental group were tested by the visual code method, the results show that the both two gel initial gelling time can be controlled in8h-12d, and gel strength can be adjusted in A～I, completely meeting the plugging requirements of the construction site.(6)Under the best conditions of gelation, PAM/HMM and PAM/TMM plugging agents were obtained respectively, the results of the plugging rate test show that the plugging performance of the two systems for tap water can both reached the oil wells water shut-off standard (≥90%), respectively,92.6and93.0%.