W. Wang, Z. Qiu, G. Chen, H. Zhong, W. Huang, J. Cao
China University of Petroleum,
Keywords: nanocomposite, shale gas, thermosensitive intelligent polymer, drilling fluid, wellbore stability
Summary:Nanotechnology has already contributed significantly to technological advances in energy industry and has the potential to revolutionize the drilling industry. Traditional blocking agents are difficult to form effective mud cake to prevent liquid penetration due to extremely low permeability and tiny pore throat of shales, while nanoscale particles can block shale pore and throat to prevent liquid into formation, thus maintaining wellbore stability and protecting the reservoir. The surface of nano SiO2 particles was modified by silane coupling agent KH570 under ultrasound to introduce vinyl functional group. Through the radical graft copolymerization of thermosensitive monomer N-isopropylacrylamide (NIPAm) and hydrophilic monomer acrylic acid (AA) onto the modified surface of SiO2 nano particles at 80℃, a series of thermosensitive poly(NIPAm-AA)/nano-SiO2 composite blocking agents with different lower critical solution temperature (LCST) values were prepared by adjusting the mole ratio between NIPAm and AA and were characterized by FT-IR, TEM and TG. The temperature response behavior was studied by light transmittance test and the sealing performance was studied by the pressure transmission test with Longmaxi Formation shale samples. Laboratory investigation showed that the blocking agents with sensitive temperature response behavior had obvious LCST value which arises with the increase of hydrophilic monomer AA. If the temperature was higher than the LCST value of the products the blocking agents played a dual role of physical plugging and chemical inhibition, slowing down pressure transmission remarkably. The surface of shale sealed by the new products presented a hydrophobic property, completely cutting off the water invasion.