| Abstract |
Surfactant-based foams have often been proposed as mobility control agents in enhanced oil recovery (EOR); however, their lack of stability under reservoir conditions has limited their field applications. This study aims at enhancing the efficiency of foam EOR by using a nanofluid composed of cocamidopropyl hydroxysultaine amphoteric surfactant and graphene quantum dot (GQD) nanoparticles extracted from Wyoming coal. Macroscale foam flooding experiments were conducted under challenging reservoir conditions (3500 psi, 115 °C, and 200,000 ppm brine salinity) to represent unconventional oil formations such as Bakken. Foam was generated through the coinjection of nanofluid and methane in strongly oil-wet core samples of different lithology (Berea sandstone, Edward limestone, and Minnesota Northern Cream (MNC) limestone), and the impact of foam quality was investigated in each outcrop. The nanofluid resulted in improved bulk foam stability due to the generation of finely structured foam of a low average bubble size (277.83 μm) and thick lamellae (98.91 μm). The in situ formation of stable foam during the core flooding tests was reflected by an improved apparent viscosity that was greatly influenced by the petrophysical properties of the rocks (i.e., pore size, pore size distribution, permeability, and wettability condition). For instance, the process of bubble generation and collapse was significantly noticed in the Edward core sample as a result of its heterogeneous pore size and nonuniform pore size distribution compared to Berea and MNC core samples. On the other hand, foam texture and the number of generated lamellae films were controlled by the fraction of gas injected (foam quality). At 60% foam quality, the foam had a very fine texture, resulting in an increased pressure gradient across the core, reduced gas mobility, and therefore improved oil sweep efficiency by diverting more gas to inaccessible oil-filled pores. As a result, the incremental oil recovery due to foam flooding was 11.5, 16.2, and 7.3% for the Berea, Edward, and MNC core samples, respectively. This study provides an in-depth understanding of the mechanisms that contribute to foam EOR in various oil-wet porous media utilizing novel nanofluid formulations. |
, Magda Ibrahim Youssif 
