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The poly(styrene-methyl methacrylate) latex particles as potential physical shale stabilizer were successfully synthesized with potassium persulfate as an initiator in isopropanol-water medium. The synthesized latex particles were characterized by Fourier transform infrared spectroscopy (FT-IR), particle size distribution measurement (PSD), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA). FT-IR and TGA analysis confirmed that the latex particles were prepared by polymerization of styrene and methyl methacrylate and maintained good thermal stability. TEM and PSD analysis indicated that the spherical latex particles possessed unimodal distribution from 80 nm to 345 nm with the D90 value of 276 nm. The factors influencing particle size distribution (PSD) of latex particles were also discussed in detail. The interaction between latex particles and natural shale cores was investigated quantitatively via pore pressure transmission tests. The results indicated that the latex particles as potential physical shale stabilizer could be deformable to bridge and seal the nanopores and microfractures of shale to reduce the shale permeability and prevent pore pressure transmission. What is more, the latex particles as potential physical shale stabilizer work synergistically with chemical shale stabilizer to impart superior shale stability.

Lost circulation often occurs in fractured formations, which was a main technological problem during drilling. Conventional lost circulation material (LCM) was often used to form a plugging zone to prevent fluid loss during drilling. The formed seal was a granular material system composed of LCMs. This paper presented the physical mechanism of the force chain within the plugging zone. The seal performance is related to the properties of LCMs. A device for testing seal performance of LCMs with long fracture was developed. The effects of LCM performance on seal integrity were investigated using a plugging device with long fracture. The results showed that the wide particle size distribution (PSD) of LCMs tended to form a strong force chain network structure within the sealing zone. Increasing the stiffness and roughness of LCMs resulted in higher breaking pressure. The addition of fiber with high length-diameter ratio could improve the shear strength of the sealing zone and form a strong force chain network structure, and it can reduce fluid loss.