Abstract
Emulsifier-free poly(methyl methacrylate–styrene) [P(MMA–St)] nanospheres with an average particle size of 100 nm were synthesized in an isopropyl alcohol–water medium by a solvothermal method. Then, through radical graft copolymerization of thermo-sensitive monomer N-isopropylacrylamide (NIPAm) and hydrophilic monomer acrylic acid (AA) onto the surface of P(MMA–St) nanospheres at 80 °C, a series of thermo-sensitive polymer nanospheres, named SD-SEAL with different lower critical solution temperatures (LCST), were prepared by adjusting the mole ratio of NIPAm to AA. The products were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, particle size distribution, and specific surface area analysis. The temperature-sensitive behavior was studied by light transmittance tests, while the sealing performance was investigated by pressure transmission tests with Lungmachi Formation shales. The experimental results showed that the synthesized nanoparticles are sensitive to temperature and had apparent LCST values which increased with an increase in hydrophilic monomer AA. When the temperature was higher than its LCST value, SD-SEAL played a dual role of physical plugging and chemical inhibition, slowed down pressure transmission, and reduced shale permeability remarkably. The plugged layer of shale was changed to being hydrophobic, which greatly improved the shale stability
Highlights
IntroductionShale gas exploration and production has attracted much attention. Given its accumulation characteristics, extended-reach horizontal wells and cluster horizontal wells were drilled to produce shale gas
At present, shale gas exploration and production has attracted much attention
When the temperature was higher than its lower critical solution temperatures (LCST) value, SDSEAL played a dual role of physical plugging and chemical inhibition, slowed down pressure transmission, and reduced shale permeability remarkably
Summary
Shale gas exploration and production has attracted much attention. Given its accumulation characteristics, extended-reach horizontal wells and cluster horizontal wells were drilled to produce shale gas. Nanoparticles are found to effectively plug shale pore throats to prevent liquid penetration into the formation, maintaining wellbore stability and protecting the reservoir (Roshan and Aghighi 2012; Rafieepour et al 2013; Wen et al 2014). Bai and Pu (2010) synthesized PMMA latex nanoparticles with an average size of 73 nm, which can be used as a lubricant in drilling fluids based on their ‘‘ball bearing’’ function to prevent pipe sticking. They can be used as a filtration reducer based on its deformability under temperature and pressure, forming a tough filter cake and sealing the micro-fissures in the formations drilled. We would adjust the transformation temperature of NIPAm by an introduction of hydrophilic monomer or hydrophobic monomer, getting smart nanoparticles with different transformation temperatures to adapt to shale formations with different temperatures
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