SMAS, namely sodium methallylsulfonate, is often copolymerized with monomers such as acrylamide to form polymers for oilfield operations like oil displacement and well cementing. Such SMAS – containing polymers demonstrate moderate long – term stability in oilfield systems. However, they are prone to degradation and efficacy loss under the impacts of shear, temperature, and microbial activity. Below is a detailed analysis along with corresponding mitigation measures:
- Long – term stability performance and degradation mechanisms affected by various factors
- Shear action: SMAS – containing polymers are likely to undergo shear degradation and efficacy reduction. In the processes of polymer solution injection, pipeline transportation, and seepage in oil reservoirs, they are constantly subjected to shear forces. SMAS has a chain transfer effect. When the content of SMAS in the polymer is high, the length of the polymer main chain will be reduced. Under the action of external shear, the molecular chains of such polymers, which already have relatively short main chains, are more likely to break. This breakage leads to a decrease in the relative molecular mass of the polymer. As the viscosity of the polymer solution is closely related to its relative molecular mass, the viscosity of the solution will drop significantly. Ultimately, the polymers fail to achieve the expected effect of increasing the viscosity of the injected water and improving the sweep volume during oil displacement.
- Temperature factor: The thermal stability of SMAS – containing polymers is relatively favorable within a certain temperature range but will degrade when the temperature exceeds a specific limit. SMAS – based copolymers, such as the SMAS – DMAM – AM terpolymer, exhibit good thermal stability in conventional oil reservoir temperatures. Nevertheless, in ultra – deep oil and gas wells with bottom – hole temperatures exceeding 140°C, or even reaching 200°C or higher, the thermal motion of the polymer molecular chains intensifies. This intense motion can break the chemical bonds in the molecular structure. Especially the amide bonds in monomers like acrylamide, which are often copolymerized with SMAS, are susceptible to thermal decomposition. This decomposition impairs the polymer’s ability to adjust the viscosity of the oilfield working fluid and control fluid loss, resulting in a significant decline in its efficacy.
- Microbial activity: There are a large number of bacteria and fungi in oilfield stratum water and working fluids. Although SMAS itself has no obvious nutrient properties, the amide and hydroxyl groups in the polymers formed by its copolymerization provide nutrients for microbial reproduction. Microorganisms like sulfate – reducing bacteria and iron bacteria can decompose the functional groups of the polymers. This decomposition destroys the molecular structure of the polymers, leading to a reduction in their relative molecular mass and performance degradation. For instance, in the long – term circulation of the polymer in the oil reservoir, microbial corrosion can make it lose its ability to adsorb on the surface of oil and water interfaces or reservoir rocks, thus failing to fulfill its intended oilfield functional requirements.
- Mitigation measures for degradation and efficacy loss
- Countermeasures against shear degradation: Firstly, optimize the synthesis process. When preparing SMAS – containing polymers, strictly control the dosage of SMAS. Avoid excessive SMAS from shortening the polymer main chain and enhance the shear resistance of the molecular structure by adjusting the monomer ratio and polymerization conditions. Secondly, improve the transportation and injection processes. Utilize positive displacement pumps during the transportation and injection of polymer solutions to minimize the shear force exerted on the solution during the transportation process. Meanwhile, optimize the pipeline layout and reduce the number of elbows and valves to lower the local shear intensity in the pipeline.
- Countermeasures against thermal degradation: On one hand, conduct copolymerization modification. Copolymerize SMAS with monomers having excellent thermal stability, such as N,N – dimethylacrylamide. The formed terpolymers can leverage the synergistic effect among different monomers to enhance the overall thermal stability of the polymer. On the other hand, add thermal stabilizers. When preparing oilfield working fluids with SMAS – containing polymers, add thermal stabilizers like sodium sulfite and thiourea. These stabilizers can inhibit the oxidation and thermal decomposition of polymer molecular chains under high – temperature conditions. In addition, for ultra – high – temperature oil wells, compound the polymers with modified nano – materials such as nano – SiO₂ modified by amino silane. This compounding can significantly improve the high – temperature resistance of the system.
- Countermeasures against microbial degradation: For one thing, add bactericides regularly. Add appropriate amounts of bactericides such as sodium dithiocarbamate and trichlorophenol sodium to the working fluid system. These bactericides can effectively inhibit the reproduction of microorganisms and prevent them from decomposing the polymers. For another, carry out cross – linking modification of the polymers. Cross – link SMAS – containing polymers with cross – linking agents like ethylene glycol dimethacrylate to form a three – dimensional network structure. This structure makes it difficult for microorganisms to decompose the polymer functional groups, thereby enhancing the microbial resistance of the polymers.
- Other auxiliary measures: Adopt low – salinity water when preparing polymer solutions to reduce the impact of salt ions on the polymer structure. Salt ions can compress the electric double layer of polymer molecules and accelerate their aggregation and precipitation. Additionally, strengthen the anti – corrosion treatment of storage tanks and pipelines. This prevents the dissolution of metal ions into the solution, as metal ions can catalyze the degradation of polymers and affect their long – term stability.
