A pore-scale experimental study of non-aqueous foam for improving hydrocarbon miscible flooding

Abstract

Mobility control in hydrocarbon miscible flooding is crucial for commercial vitality where severe reservoir heterogeneity causes poor sweep efficiency. This study introduced a new concept of non-aqueous foam-assisted hydrocarbon miscible flooding in water-sensitive oil formations. This process involves the injection of a non-condensable gas (i.e., nitrogen or methane) and a raw mixture of NGLs (MNGLs) with a foaming additive to improve displacement and sweep efficiency. Foaming a light hydrocarbon liquid and the impact of non-aqueous foam on miscible displacement are the main focuses of this study. n-Pentane was used as a MNGLs (solvent) model for foam stability tests. Transient foam propagation and rheology were directly visualized and characterized based on the apparent gas (nitrogen) viscosity associated with foam texture and fluid saturations. Oil recovery factors were directly related to different degrees of in-situ foaming. For the injection of a solvent slug followed by a gas drive, the displacement of oil became unstable as nitrogen fingered through the solvent-oil mixing zone, resulting in a high residual liquid saturation. However, gas fingering was significantly hindered as the solvent was injected with a foaming agent. Dynamic fluid distribution indicate that the improved oil recovery could be attributed to the propagation of foam in the swept zone, which provided essential flow resistance for better displacement stability. To investigate the effect of initial gas saturation in the reservoir on flow behavior, a slug of gas was injected before solvent injection. Delayed solvent breakthrough and better sweep efficiency were observed in the presence of foam due to the reduced liquid phase mobility in preferential flow paths and the diversion of solvent into small pores by the trapped gas at the displacing front. Furthermore, it was possible to obtain stable foam flow with an apparent viscosity of 20 times greater than the solvent viscosity.