Abstract

SAGD (steam assisted gravity drainage) is known as the main technology to tackle the exploitation of heavy oil and oil sand resources in Alberta. The oil industry seems to be well-educated today about SAGD's challenges and opportunities. Enhancing the efficiency of SAGD operations remains an area of investigation as it is tied to economic and environmental measures. Use of chemical additives and foam with SAGD is a strategy proposed on this account.

Foam is dispersion of gas in a continuous water phase with thin films (lamella), acting as a separator. Given its sensitivity to oil distribution, foam tends to reside in higher permeability layers with less residual oil. Thermally stable surfactants are essential to maintain the foam life because surfactants stabilize lamella by decreasing the water-gas interfacial tension. Adding surfactants also lowers the interfacial tension at the water-oil interface and further produces water in oil or oil in water emulsion. In situ emulsion generation is thus another active mechanism that is involved as a result of surfactants presence.

Due to the above properties, steam movement is hindered, and gravity override is consequently limited, thereby resulting in high injection pressure that thoroughly displaces oil. Also, foam injection is conducive for blocking thief zones and decreasing channeling. In terms of emulsification, oil in water emulsion flow decreases water permeability created by emulsion droplets entrapment in throats, transferring the injection flow into poorly exploited areas. More trapped oil is mobilized by interfacial tension drop. The existence of water in oil emulsion contributes to heat transfer because the generation reaction is exothermic. All mechanisms mentioned are incorporated to illustrate CAFA-SAGD (chemical additives and foam assisted SAGD) performance and compare it with SAGD in both homogeneous and heterogeneous reservoirs using CMG® STARS. The reservoir under study is analyzed with low permeability layers, top water, bottom water, and lean zones for the heterogeneous case. The surfactants properties and foamibility are considered through appropriate reactions introduced into the simulator. The phase behavior for emulsification regulates different relative permeability regimes into the oil flow. We find that adding additives contributes to higher production and leads to less steam consumed.

This study incorporates viscosity reduction, mobility control, interfacial tension drop, and emulsification mechanisms to present the effects of chemical additives and foam towards SAGD performance. Our results indicate that using additives with SAGD can maintain a uniform steam chamber growth while reducing the heat loss to overburden. It has a significant long-term oil production capability.

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