Reduction of the effective shear viscosity in polymer solutions due to crossflow migration in microchannels: Effective viscosity models based on DPD simulations

Conformations and dynamic behaviors of confined wormlike chains in a pressure-driven flow

The conformations and dynamic behaviors of wormlike chains confined by a slit in a pressure-driven flow were investigated using dissipative particle dynamics method. The wormlike chains exhibit varying conformations due to the varying shear stresses across the slit. The wormlike chain solution can be well described by the power-law fluid, and the power-law index decreases with the increase in chain rigidity. We also presented that the wormlike chain undergoes tumbling motion in the vicinity of the wall in the presence of pressure-driven flow. We also found that the wormlike chains can migrate both away from the wall and slightly away from the slit center, and the migration away from the slit center increases as the chain rigidity is increased because of hydrodynamic interactions induced in a more rigid wormlike chain.

Pore-Scale Flow Fields of the Viscosity-Lost Partially Hydrolyzed Polyacrylamide Solution Caused by Sulfide Ion

The rheology of a partially hydrolyzed polyacrylamide (HPAM) solution plays an important role in its oil recovery during polymer flooding. However, multiple factors in brine, such as sulfide ions, cause a dramatic loss in the viscosity and oil recovery. To better understand the sulfide-induced viscosity loss and the consequent flow mechanisms in pore networks, the morphology of polymer solutions with and without sulfide ion was observed by scanning electron microscopy; and the variations of the pore scale flow fields were demonstrated by a microscopic visualization seepage experiment combined with Micro-PIV (Microscale Particle Image Velocimetry). The results showed that, with the presence of sulfide ion, the microstructure of the polymer changed from a uniform three-dimensional network structure to loose and uneven floccules, which resulted in viscosity loss (over 70% with 5-mg/L sulfide ion). Moreover, higher concentrations of sulfide ions (5 mg/L and 10 mg/L) resulted in earlier shear thinning characteristics than those with lower sulfide concentrations. Due to viscosity loss, the average flow velocity in the main stream of the microscopic seepage experiment increased more significantly than that without sulfide. However, the viscosity loss alone cannot independently explain the severe viscous fingering during the subsequent post-water flooding, which was about five times greater than that of the primary water flooding in terms of the velocity ratio between the mainstream and margin. A further pore-scale flow field analysis exhibited an eccentric and a bimodal velocity distribution in the throat along the radial and axial directions, respectively. The former distribution indicated that the adsorbed polymer on the pore wall was broken through by hydraulic shear due to the collapsed structure caused by sulfide ion. The latter suggested that another sulfide-induced impact was an earlier-occurring non-Newtonian characteristic with a low shear rate. Therefore, instead of viscosity loss, elastic loss is the dominant mechanism affecting the characteristics of the aggregate flow field under the action of sulfide. Microscopic flooding combined with Micro-PIV is a feasible and essential method to reveal pore scale flow mechanisms.

Flow behavior of thermo-thickening associative polymers in porous media: effects of associative content, salinity, time, velocity, and temperature

Abstract

Above a critical temperature, thermo-thickening associative polymers (TAPs) have a superior ability to decrease the mobility of the water phase, compared to traditional polymers for enhanced oil recovery. The ability to decrease the mobility, will be amplified at low flow velocities, and by the presence of salt, and is much higher in porous media than would be expected from bulk viscosity. In this work, we have examined TAPs ability to reduce the mobility, i.e., to increase the resistance factor. We have studied the effect of increasing the associative content, changing the porous media, changing the salinity, and scaling up the size of the porous media. How the resistance factor evolved, was studied as a function of temperature, velocity, and time. We found that a critical associative content or critical concentration of polymer was needed to achieve thermo-thickening in the porous media. As expected, thermo-thickening increased by increasing the salinity. For the relative homogenous clastic porose media investigated here, ranging from ~ 1Darcy sandstone to multidarcy sand, type of porous media did not seem to have a significant impact on the resistance factor. Time and amount of polymer injected is a critical factor: The buildup of thermo-thickening is delayed compared to the polymer front. For our tests with the weaker systems, we also observed a breakdown of the associative network at very low injection rates, possibly caused by the formation of intramolecular association.

Article highlights

Key findings from our tests of thermo-thickening associative polymer for enhance oil recovery operations:

Effect of Aggregation and Adsorption Behavior on the Flow Resistance of Surfactant Fluid on Smooth and Rough Surfaces: A Many-Body Dissipative Particle Dynamics Study

To study the effect of surfactant on the resistance of wall-bound flow, the adsorption and aggregation behaviors of surfactant fluid on both smooth and groove-patterned rough surface are investigated through many-body dissipative particle dynamics (MDPD) simulation. The MDPD models of surfactants were carefully parametrized and have been validated to be able to simulate the aggregation and adsorption behavior of surfactants. The simulation results show that the surfactant in laminar flow can only increase the flow resistance on the smooth surface. On the rough surface, surfactant with strong adsorption performance on the channel wall shows a drag reduction effect at moderate concentration. The surfactant with weak adsorption properties can enhance the flow resistance, which is even more significant than that of those surfactants with no adsorption capacity. Although heating (high temperature) can generally reduce the viscosity and flow resistance of surfactant fluid, it would cause a poor drag reduction efficiency. It may arise from the destruction of the adsorption layer and the interruption of the fluid/boundary interface. Surfactant adsorption can tune the roughness of the fluid boundary on either the smooth or rough surface in a different manner, which turns out to be highly correlated to the change in flow resistance. Compared with the adsorption layer, surfactant in the bulk fluid makes a greater contribution to enhancing the flow resistance as the concentration rises. This study is expected to be helpful in guiding the application of surfactants on the micro- and nanoscale such as lab-on-a-chip nanodevices and EOR in a low-permeability porous medium.