Preparation of ultra-high temperature and high salinity resistant polymer microsphere and its property evaluation

Polymer microspheres have been used in the field of heterogeneous reservoir profile control, but their temperature and salt resistance still need to be improved. In this paper, N’N-dimethylacrylamide (DMA) and sodium styrene sulfonate (NaSS) were used as monomers, divinylbenzene (DVB) was used as cross-linker, and inverse emulsion polymerization was adopted to preparation the ultra-high temperature resistant polymer microsphere. After the investigation of the influences of emulsification shear time, monomer concentration, mass ratio of DMA to NaSS, and DVB addition on the polymerization result, a kind of polymer microspheres (PNS microspheres) that could maintain long-term stability in different brines (including seawater) at 150 °C for 45 days was prepared. The temperature and salt resistance of PNS microspheres are significantly better than that of polyacrylamide microspheres. The size of PNS microspheres is about 30 μm, and they can expand by about 2–4 times in low salinity brine at 150 °C, while they do not expand in seawater. Plugging effect experiment results showed that PNS microspheres can achieve a plugging rate of over 90 % for porous media with a water permeability ≤ 600 mD. T 2 spectrum of PNS microsphere displacement effect presented that it can effectively block the large pore throats and achieve micro fluid flow diversion, while oil displacement effect showed it can improve oil recovery of about 20 %. This work provides a viable candidate material expected to be applied for profile control in offshore high-temperature heterogeneous reservoirs.