Combined flooding systems with polymer microspheres and nonionic surfactant for enhanced water sweep and oil displacement efficiency in heterogeneous reservoirs

Preparation of Preformed Submicron Crosslinked Polymer Coils for Conformance Control in Low-Permeability Reservoirs

With the increasing development of low-permeability reservoirs, the significance of conformance control treatment has risen considerably. To address the conflict between injectability and plugging performance, as well as to enhance the deep migration capacity of conformance control agents, preformed submicron crosslinked polymer coils (SCPCs) have been manufactured using aqueous solution dispersion polymerization. Fourier transform infrared and scanning electron microscopy were employed to examine the chemical structure and micromorphology, while particle size distribution, zeta potential, rheological, and filtration properties were analyzed. The effectiveness of conformance control was confirmed through the parallel core displacement. The effective particle size of SCPCs was at a submicron level (500~800 nm). SCPCs exhibit a transitional threshold concentration between gel and sol states (0.25 wt%~0.5 wt%). SCPCs can efficiently block the 1.2 μm microporous filter membrane. The filtration time is up to 67.8 min. SCPCs can improve the water absorption rate of lower permeability cores from 21.21% to 57.89% with a permeability difference of 5. Therefore, SCPCs have good injectability, plugging performance, and deep migration capacity and can be used for conformance control in low-permeability reservoirs.

Research of a Surfactant Gel with Potential Application in Oilfield

In this study, a viscoelastic surfactant gel was composed using erucoylamine propyl betaine and other additives. The formulation of this viscoelastic surfactant gel solution was determined as: erucamide propyl betaine:oleic acid amide propyl betaine:octadecyl hydroxyl sulfonate betaine = 1.7%:1.36%:0.01%. Then the performance of viscoelastic surfactant gel fluid was evaluated. The results showed that the viscoelastic surfactant gel has good temperature resistance and salt resistance. At 50°C, the apparent viscosity reaches the maximum value, 37 mPa · s, and it displays high shear resistance under the shear rate of 170 s–1, with the viscosity retention of 83.3%. Kerosene (1%) can completely break the gel within 2 h, which can convert the gel into a surfactant solution soon. Also the gel shows high emulsion ability, which can benefit the oil displacement in oilfield. Finally this gel can enhance the oil displacement rate as high as 28%.

Research on the mechanisms of polyacrylamide nanospheres with different size distributions in enhanced oil recovery

Crosslinked polyacrylamide microspheres are widely used as in-depth flooding agents in petroleum development due to their unique properties of thickening, salt-resistance, high-temperature resistance, low cost, etc. To solve the problem of their injections in heterogeneous reservoirs, polyacrylamide nanospheres were synthesized. However, mechanisms of polymer nanospheres in enhanced oil recovery were not investigated comprehensively. In this study, we synthesized polymer nanospheres with different size distributions and studied their mechanisms in enhancing the oil recovery. First, the effects of polyacrylamide nanospheres in enhanced oil recovery of heterogeneous sand-packed tubes was explored by sand-packed tube oil displacement experiments. Second, the rheological properties of polyacrylamide nanosphere dispersion were explored using a rheometer. Third, through the visual microchannel experiment, the mechanism of polymer nanosphere emulsion on the removal of the residual oil film was explored. Finally, through the crude oil removal experiment, it was found that polymer nanospheres with a particle size of about 54 nm can cooperate with surfactants to accelerate the removal of oil droplets.

In this study, we synthesized polyacrylamide nanospheres with different size distributions and found that the oil displacement mechanisms of polyacrylamide nanospheres are composed of three aspects.