No abstract

No abstract

Wettability alteration is an important mechanism in surfactant-facilitated enhanced oil recovery (EOR) in oil-wet carbonate reservoirs. An in-depth understanding of how surfactants influence the wettability of calcite surfaces is of crucial importance. In this study, atomistic molecular dynamics simulations were used to elucidate how the nonionic and anionic surfactants influence the wettability at the corners of angular calcite pores. A multicomponent oil model was constructed based on a chemical analysis of an unconventional reservoir crude oil. It was found that the inclusion of the calcite surface water layer caused a significant decrease in the attraction between the surface and the surfactant molecules from hundreds of kJ/mol to essentially zero. The surface water layer is therefore critical for an accurate description of calcite wettability. Simulated flooding of the oil-filled calcite pore with both types of surfactants was compared to that with blank brine. It was found that the tested surfactants alter the wettability of the calcite surface mainly by hydrophobic interactions with the adsorbed polar oil components and by weakening the interactions between polar and nonpolar oil components. The wettability alteration resulted in a 20–30° reduction in contact angles, while the ratio of the polar-to-nonpolar oil components within the pore decreased by approximately 50% by the surfactants as compared to just brine. The results presented in this work can provide guidance for selection of the most effective surfactants for oilfield applications.

No abstract

Polymer gel treatment is a proven cost-effective method to control excessive water production and improve sweep efficiency in many mature oilfields; however, it is worth noting that there exist differences between gelation behavior and morphology in bulk and porous media, which are directly related to the success of a gel treatment. In this study, the gelation behavior and morphology of resorcinol-hexamethylenetetramine-HPAM gel in bulk and porous media were studied. Results revealed that the differences between the gelation time and morphology in bulk and porous media were obvious. The relationship between bulk gelation time and static gelation time in porous media was correlated. Dynamic gelation behavior in porous media confirmed that the gelation could occur during flow in porous media and the gelation location can be inferred to determine gel placement. This study could provide the basis for determining well shutoff time and understanding the blocking mechanism in porous media.