New Insights into Steam-Solvent Co-injection Process Mechanism

Abstract

We present results of a detailed investigation of the steam-solvent co-injection process mechanism using a homogeneous numerical model and three different solvents. The mechanistic model developed in this study describes coupled heat and mass transfer at the chamber boundary and its implications in detail. We present a composite picture of interplay of the process variables, the important phenomena occurring in the different regions of the reservoir and their consequences for oil recovery. The results are corroborated by literature experimental results and field data. The model will help with selecting the best operating strategy for a given reservoir.Results show that the injected steam and solvent vapor condense near the steam chamber boundary. The temperature near the chamber boundary drops because of a reduction in the partial pressure of steam.The condensed steam-solvent mixture drains outside the chamber boundar leading to the formation of a mobile liquid stream where heated oil, water and condensed solvent flow together to the production well. The condensed solvent and water are immiscible and therefore, form separate flow streams. The condensed solvent mixes with the heated oil in the water-oil stream and reduces its viscosity beyond that caused by heating alone, resulting in higher oil production rate. As the steam chamber expands laterally because of continued injection and temperature in the hitherto drainage region increases, part of the condensed solvent mixed with oil evaporates. This lowers the residual oil saturation in the steam chamber. Therefore, ultimate oil recovery with steam-solvent co-injection process is higher than that in steam only injection. The higher the solvent concentration in oil at a location, the greater is the reduction in the residual oil saturation at that location.Thus, steam-solvent co-injection causes a higher oil production rate because of an additional reduction in oil viscosity and a higher ultimate recovery because of a reduction in residual oil saturation. IntroductionSteam Assisted Gravity Drainage (SAGD) has become the technology of choice for exploiting the huge resource base of bitumen. There are more than ten commercial SAGD projects in Canada. The field performance indicates that the process offers high production rate and high ultimate recovery. However, this process requires a large volume of steam injection. The observed steam-oil ratio (SOR) in the field is in the range of 3-5 (Jimenez, 2008). A large usage of steam affects the project economics adversely and also has a detrimental impact on the environment.

Semianalytical Modeling of Steam/Solvent Gravity Drainage of Heavy Oil and Bitumen: Unsteady-State Model With Curved Interface

“…However, the high cost of solvents makes it important to select the best solvent for a particular reservoir and to ensure that an optimal concentration of solvent is used. Steam/solvent coinjection has been successfully tested in field operations, resulting in improved oil rate, thermal efficiency, and reduced water requirements compared with the steam-only method (Gupta and Gittins 2006;Leaute and Carey 2007;Dickson et al 2013;Dittaro et al 2013).…”

Effect of Bitumen Viscosity and Bitumen-Water Interfacial Tension on the Efficiency of Steam Assisted Bitumen Recovery Processes

“…Almost all SAGD and ES-SAGD studies focused on the mobility of bitumen in and at the edge of the steam chamber by considering mainly bitumen viscosity reduction by thermal and/or solvent effects (Zhao et al 2005;Gittins 2006, 2012;Ayodele et al 2009;Sharma and Gates 2011;Jha et al 2012). ES-SOLVENT process concepts evolved from this principle and were studied extensively.…”