Steam-Surfactant-Foam Modeling in Heavy Oil Reservoirs

Abstract

Abstract Steam foam is a hybrid and novel method of the thermal and chemical flooding to improve the sweep efficiency of steam for producing heavy crude oils. Steam injection is a mature process to substantially reduce the oil viscosity in heavy oil reservoirs to increase its mobility. Steam flooding is an unstable displacement since the gravity of steam causes poor vertical sweep efficiency due to the gravity override in thick high permeability pay zones and poor areal sweep efficiency in high permeability channels with high connectivity. On the other hand foam reduces the mobility of steam by stabilizing the liquid lamellae that cause some or all of the steam to exist as a discontinuous phase. Therefore, foam plugs large pores to divert the flow into the low permeability zones and controls gravity override. Foam increases the pressure gradient slightly in the steam swept regions and leads to heating oil more efficiently when steam diverts into the cold unswept regions. Furthermore, surfactant mobilizes the high viscous oil by emulsification and reduction of interfacial tension. The synergy of steam, surfactant, and foam has the potential to greatly improve the recovery of heavy oil reservoirs. Based on a literature survey, steam foam injection has been conducted in both laboratory corefloods and few field pilots. On the other hand, existing numerical simulators have not been able to capture the mechanisms involved in such a process. In this paper, we present the development and implementation of a new robust steam formulation in a four phase chemical flooding reservoir simulator (UTCHEM) to model and understand the contribution of each mechanism such as viscosity reduction, emulsification, and foam for mobility control. Results illustrate that the steam foam process controls the mobility of steam to avoid incomplete vertical sweep due to gravity segregation. Formation of the emulsion phase by condensing steam along with the presence of water leads to an increase in the emulsion viscosity and thereby decreases water production. The presence of surfactant and emulsification of oil either as water in oil or oil in water emulsions can also impact the displacement and propagation of viscous oil. The mechanistic understanding of steam foam process and improvement of the heat transfer compared to conventional steam flooding is a key finding in this research to optimize the technology that unlocks heavy oil reservoirs with favorable economics.