Many oilfields report that the viscosity of polymers in high-salinity reservoirs will decrease significantly. In this paper, molecular dynamics simulations were conducted to investigate the molecular configuration and network of hydrolyzed polyacrylamide (HPAM) molecules in high-salinity formation-water and the viscosity changes from the microscopic dense to dilute phase. In addition, the viscosity of HPAM/formation-water solution was measured to verify and compare with simulation results. Simulation and experimental results show that the molecular network of the microscopic dense phase is essential for the apparent viscosity. The calculated apparent viscosity could decrease 37% as the net-shape molecular network of the microscopic dense phase is broken by calcium ions, which is similar to our experimental results. This paper improved our understanding of the mechanisms of polymer viscosity alteration in high-salinity formation-water and provided insights that can be used to improve the strategy of enhanced polymer flooding and the novel polymer gel formula.

The low-frequency pulse wave makes the velocity of the fluid in the reservoir fluctuate dramatically, which results in a remarkable inertia force. The Darcy’s law was inapplicable to the pulse flow with strong effect of inertial force. In this paper, the non-Darcy flow equation and the calculation method of capillary number of pressure pulse displacement are established. The pressure pulse experiments of single-phase and two- phase flow are carried out. The results show that the periodic change of velocity can decrease the seepage resistance and enhance apparent permeability by generating the inertial force. The higher the pulse frequency improves the apparent permeability by enhancing influence of inertial force. The increase of apparent permeability of high permeability core is larger than that of low permeability core, which indicates that inertial force is more prominent in high permeability reservoir. For the water-oil two-phase flow, inertia force makes the relative permeability curve move towards right, and the equal permeability point becomes higher. In other words, with the increase of capillary number, part of residual oil is activated, and the displacement efficiency is improved.

For high pressure and high temperature shale gases, the adsorption density would approach to or be more than the maximum density. To investigate the adsorption mechanism and calculate the adsorption isotherms, methane molecules adsorb into the organic nanopore under 0 to 80MPa and 430K are simulated using molecular dynamic method. Based on simulation results, the analytical model of adsorption in organic nanopores for high pressure and temperature is developed, which is verified by our adsorption isotherms measurements. Simulation results reveal the adsorption mechanism for high pressure and temperature shale gases is that the adsorbed layer is becoming compressed, the density of which is more than maximum density. The compressed adsorbed layers have high mobility and contribute to more gas production of deep- and ultra-deep shale gases. when the pressure decreases to less than 40MPa, the mobility of adsorbed layers decreases. These results suggest the development of deep- and ultra-deep shale gases could take an advantage of high mobility adsorption and high pressure in small organic nanopores.