What kinds of filtrate reducer are there for drilling fluid? What is the mechanism of filtrate reducer for drilling fluid?

Filtrate reducer products can be divided into two categories: granular materials, water-soluble polymers and organic materials. Among granular materials, latex has become a research hotspot at home and abroad because of its good filtration loss reduction, gas channeling prevention and toughening effects, and its research progress will be listed separately below. At present, filtrate reducer products are mostly water-soluble polymers and organic materials, which can be divided into modified natural products and synthetic polymers. In addition, a lot of research has been done on environmental protection filtrate reducer abroad.

1 modified natural product filtrate reducer

Modified cellulose is a kind of water-retaining agent widely used in water-soluble natural products. Modified cellulose that can be used as water loss reducer includes CMC (carboxymethyl cellulose), HEC (hydroxyethyl cellulose), CMHEC (carboxymethyl hydroxyethyl cellulose) and so on. CMC flocculates cement slurry, which has strong retarding property, so it is no longer used. HEC's comprehensive performance is acceptable, and its application is not much. CMHEC is widely used abroad, but it is rarely produced in China, and there is no application report. The common disadvantages of modified cellulose are poor water solubility, high viscosity, poor temperature resistance and lagging development of cement strength. Chemical graft copolymerization and introduction of other functional monomers are good methods to improve the performance defects of cellulose.

2. Polymer filtrate reducer

There are many kinds of synthetic polymer fluid loss additives with excellent properties, and some natural products have incomparable characteristics, so they have become the focus of researchers all over the world.

1) nonionic polymer

PVA (polyvinyl alcohol) system is a kind of nonionic fluid loss reducer widely used in China, which has unique advantages, such as G60S of Tianjin CNPC Boxing Company. The operating temperature of the system can reach 95℃. Above this temperature, the cross-linking bond is destroyed and the filtration performance becomes poor. In addition, the salt tolerance (NaCl) of the system is poor, which is usually less than 5%. In order to improve the poor temperature resistance and salt resistance of PVA system, PVA can be modified by chemical crosslinking, such as condensation reaction between alcohol group of PVA and condensation agent such as aldehyde or acid to obtain partially crosslinked PVA. Chemically crosslinked PVA can be used alone without crosslinking agent such as borax. The temperature resistance can reach 120℃, the salt resistance can reach 8%, and the filtration rate can be controlled below 50mL.

2) anionic polymer

Anionic polymer is a kind of filtrate reducer with the most extensive research at home and abroad and the largest variety of products. Its comonomers include nonionic and anionic monomers. The nonionic monomers mainly include AM (acrylamide), NVP(N- vinylpyrrolidone), NNDMA(N, N- dimethylacrylamide), St (styrene), VI (vinylimidazole), VFA (vinylformamide), VP (vinylpyridine), VMAA(N- methyl -N- vinylacetamide) and so on. Among these monomers, AM is easy to hydrolyze, so the content in the copolymer should not be too much. NNDMA introduces groups that are not easy to hydrolyze, and its high temperature resistance is obviously enhanced. However, this monomer is expensive and is still in the pilot stage in China. Anionic monomers mainly include two types: one is sulfonate monomers, such as AMPS(2- acrylamido -2- methylpropanesulfonic acid), SS (styrene sulfonate), VS (ethylene sulfonate) and PS (propylene sulfonate); The other is carboxylate monomers, such as AA (acrylic acid), MAA (methacrylic acid), HEA (hydroxyethyl acrylic acid), IA (itaconic acid) and so on. AMPS has strong temperature and salt tolerance, high polymerization activity and wide application, and has formed large-scale production in China.

3 environmental protection water loss reducer

With people's increasing attention to environmental protection, in recent years, foreign researchers have increased the research and development of environmentally friendly filtrate reducer. The so-called environmental protection filtrate reducer refers to filtrate reducer products with good biodegradability. At present, the main ways to develop environmental protection filtrate reducer are: (1) developing natural products with filtrate reducer function; (2) modifying the existing natural product filtrate reducer to expand its application range; (3) Developing filtrate reducer which is stable in strong alkaline environment and degradable in neutral water medium; (4) crosslinking the low molecular weight polymer with a degradable crosslinking agent to obtain a high molecular weight filtrate reducer; (5) modifying the degradable synthetic polymer to make it have the function of fluid loss reduction; (6) Develop a synthetic polymer filtrate reducer which is similar in structure to natural products and can be degraded by microorganisms.

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