In oilfield applications, SMAS (sodium methallyl sulfonate) has become a research focus due to its ability to introduce sulfonic acid groups into polymers to enhance their thermal stability and salt resistance. Current research hotspots mainly concentrate on the development of new copolymer systems, the expansion of application scenarios, and the innovation of efficiency-enhancing technologies. The details are as follows:
- New Copolymer Systems
- Ternary Hydrophobically Associating Copolymer System: To address the poor adaptability of conventional oil-displacing agents like partially hydrolyzed polyacrylamide (HPAM) to high-temperature and high-salinity oilfields, researchers have developed a ternary water-soluble hydrophobically associating copolymer using SMAS (methyl stearate methacrylate), acrylamide (AM), and sodium styrenesulfonate (SSS) as raw materials. This copolymer is synthesized via dispersion polymerization. When the content of both SMAS and SSS is 5%, the copolymer solution achieves maximum apparent viscosity. It also exhibits a salt-thickening effect with increasing NaCl concentration, and its apparent viscosity decreases only slowly with rising temperature. Its initial decomposition temperature reaches 275°C, demonstrating excellent thermal stability and overcoming the drawbacks of conventional polymers.
- SMAS-modified Oil-absorbing Resin Copolymer System: A ternary composite oil-absorbing resin (MMA – SMAS – St) has been synthesized to tackle the severe leakage problem of oil-based drilling fluids (OBDF). Styrene is used to enhance the resin’s rigidity, while octadecyl methacrylate optimizes its oil absorption and expansion properties. At 160°C, this copolymer resin maintains a strong oil absorption expansion rate of 12.5g/g and can effectively seal fractures of 0.25μm, 0.5μm, and 0.75μm widths. Adding 3% of this resin to OBDF significantly improves the fracture-sealing effect, which is crucial for stabilizing the wellbore during oilfield drilling.
- SMAS-derived Imide Copolymer System: Through reversible addition-fragmentation chain transfer polymerization, SMAS is copolymerized with styrene to form a styrene-maleic anhydride copolymer, which is then converted into a styrene-octadecylmaleimide copolymer (SnoDMIs) via amidation and imidization reactions. When the branch content of SnoDMIs reaches about 45mol%, the molecular weight is around 3500Da, and the imidization degree is 100%, it shows optimal performance as a flow improver for high-asphaltene crude oil. It can reduce the viscosity and yield stress of crude oil by over 90%, effectively solving the problem of poor fluidity in high-asphaltene crude oil exploitation and transportation.
- Expanded Application Scenarios
- Plugging of Fractured Sandstone Reservoirs: The SMAS-based strong gel plugging agent, composed of a main agent, cross-linking agent, and retarder, has emerged as a key solution for fractured sandstone oilfields where conventional water plugging methods are ineffective. By adjusting the retarder dosage, its gelation time can be controlled within 12 – 144h. In experiments, at 50°C, the gel achieves a core plugging rate exceeding 99.9%, and this rate remains above 99.8% even after injecting 50PV of water. In the Huoshaoshan oilfield, which has fractured ultra-low permeability sandstone reservoirs, the application of this plugging agent has increased water-flood recovery efficiency and added proven reserves of 150,000 tons.
- High-permeability Zone Plugging in Thick Oil Layers: For thick oil layers with serious heterogeneity and ineffective circulation of injected water due to long-term water flooding, SMAS-modified polymer gel is used to plug high-permeability zones. After plugging, the flow direction of the injected water changes, forcing it to flow into low-permeability oil-bearing layers. This enhances the sweep efficiency of the injected water in thick oil layers, achieving oil increment and water reduction. Field tests have verified its effectiveness in improving the development effect of thick oil layers.
- High-salinity Reservoir Oil Displacement: SMAS introduces sulfonic acid groups into polymer chains, endowing copolymers with outstanding salt resistance. Polymers prepared by copolymerizing SMAS with monomers such as acrylamide and acrylic acid can maintain stable performance in high-salinity reservoir environments without performance degradation. This enables their extensive application as oil displacement agents in high-salinity oilfields, filling the gap where conventional oil displacement agents fail due to salt-induced viscosity loss.
- Efficiency-enhancing Technologies
- Optimization of Copolymer Synthesis Process: In the synthesis of SMAS ternary hydrophobically associating copolymers, optimizing solvent ratios and dispersant dosage can significantly improve copolymer efficiency. For instance, when the volume ratio of DMF to ethanol is 40:60 and the dispersant PVP content is 4%, the apparent viscosity of the copolymer system reaches its peak. Controlling the initiator concentration can adjust the particle size of copolymer microspheres within the range of 1.5 – 7.8μm, ensuring good dispersibility and enhancing the adaptability of the copolymer in different reservoir pore throats.
- Gel Performance Regulation Technology: The gelation time of SMAS-based strong gel is flexibly adjusted by controlling the dosage of the retarder, enabling it to adapt to different construction requirements. For example, in scenarios requiring rapid plugging, reducing the retarder dosage shortens the gelation time; in deep reservoir plugging, increasing the dosage extends the gelation time, ensuring the gel can flow to the target fractured zone before solidifying. This regulation technology ensures the long-term effectiveness of the gel in plugging, with the breakthrough pressure gradient remaining no less than 3.4MPa/m.
- Compound Synergy with Auxiliaries: Compound SMAS copolymers with auxiliary agents to enhance application efficiency. For example, when preparing oilfield fluid loss reducers and dispersants, copolymerize SMAS with monomers like acrylamidopropyltrimethylammonium chloride and diallyldimethylammonium chloride. The synergy between different monomers enhances the high-temperature and salt resistance of the product, enabling it to maintain stable fluid loss reduction and dispersion performance under harsh downhole conditions, reducing the frequency of drilling fluid replacement and improving construction efficiency.
