A Novel Foam Concept With CO2 Dissolved Surfactants

Abstract

Abstract CO2 injection has become the most attractive solution for enhanced oil recovery (EOR). However, this process frequently suffers from viscous fingering, gravity override, and channeling of CO2 in heterogeneous formations and the inefficient displacement of oil in below-miscibility-pressure reservoirs. These challenging issues are closely related to the very limited ability to control CO2 mobility. CO2 foam stabilized with CO2 soluble surfactants has exhibited more economical and technical advantages in effective control of CO2 mobility in porous media than the existing direct methods of CO2 viscosification. An integrated research framework was developed to strengthen the role of molecular design for these features as wells as provide a better understanding of foam behavior with complex formation of viscous water/oil or oil/water emulsions. A simple block model was developed in CMG/STARS to demonstrate the advantages of the novel foam concept over the conventional foam processes in the field. We proposed a novel injection strategy which involves dissolving the surfactant in the CO2. This method drastically lowers the injection costs, reduces the loss of surfactant onto the rock surface due to adsorption, and improves in-situ foam generation to significantly increase oil recovery. Two different novel methods, continuous CO2-dissolved-surfactant injection and water-alternating-gas with CO2-dissolved-surfactant injection, have been studied in this paper. Foam corefloods performed with carbonate core show that CO2-dissolved surfactants greatly reduce the mobility of the injected gas compared to conventional injection strategies. This is consistently observed in the numerically simulated foam process at the field level. Introduction CO2 flood have been applied worldwide as a routine EOR technology, particularly for reservoir candidates whose pressures are above minimum miscibility pressure (MMP). However, reservoir heterogeneity and high gas mobility reduce sweep efficiency and drastically decrease oil recovery (Renkema and Rossen, 2007). For formations with relatively high vertical permeability and vertical well pattern, the injected CO2 tends to rise to the top of the reservoir due to its low density and overrides the bottom oil-rich zone, leading to early gas breakthrough. CO2 displacement could be improved by water-alternating gas (WAG) injection. The efficiency of this process relies on the ability to reduce gas relative permeability in the presence of the aqueous phase and to promote gas trapping in depleted zones that diverts both the injected gas and water into the oil-rich zones. However, WAG injection has frequently encountered some important issues such as the reduction of CO2-oil contact in the presence of water and low injectivity commonly observed in carbonate reservoirs. Gravity segregation tends to impair further the advantages of this injection strategy. This has inspired the application of surfactant stabilized CO2 foam to improve CO2 conformance as foam could generate not only a large amount of stable trapped gas but also a significantly high local pressure gradients induced by aqueous foam films that disperse the gas phase.