Noncondensable gas steam-assisted gravity drainage S. Canbolat a , S. Akin a , A.R. Kovscek b, * a Petroleum and Natural Gas Engineering Department, Middle East Technical University, 06531 Ankara, Turkey b Department of Petroleum Engineering, Stanford University, Stanford, CA 94305-2220, USA Received 21 August 2003; accepted 19 April 2004 Abstract To investigate steam-assisted gravity drainage (SAGD) mechanisms, experiments with and without carbon dioxide or n- butane mixed with steam were conducted in a scaled physical model. It is packed with crushed limestone premixed with a 12.4j API heavy-oil. Temperature, pressure, production data, and the asphaltene content of the produced oil were monitored continuously during the experiments. For small well separations, the steam condensation temperature and the steam – oil ratio decreased as the amount of carbon dioxide increased. The heavy oil became less mobile in the steam chamber due to lower temperatures and more viscous oil. Thus, the heating period was prolonged and the cumulative oil recovery as well as the recovery rate decreased. Less oil recovery was obtained as the fraction of carbon dioxide injected increased. Little or no change in oil recovery, and the rate of oil recovery, was observed for greater well separations regardless of the fraction of carbon dioxide in the injection gas. Similar behavior was observed when n-butane was injected along with steam instead of carbon dioxide. Cumulative oil recovery, rate of oil recovery, and steam –oil ratio decreased independent of well separation compared to a reservoir with no initial noncondensable gas. These experimental results add to the state of the art understanding of thermal gravity drainage processes. The addition of noncondensable gases during steam-assisted gravity drainage was not beneficial to oil recovery. Nevertheless, experiments do teach that steam injection is effective for producing heavy-oil saturated limestone. D 2004 Elsevier B.V. All rights reserved. Keywords: Gravity drainage; Heavy oil; Thermal oil recovery; Noncondensable gases 1. Introduction A recovery mechanism is required that lowers the viscosity of heavy oil so that it flows easily to a production well. Conventional thermal processes, such as cyclic steam injection, and steam-assisted gravity drainage (SAGD) are based on thermal vis- cosity reduction and gravity drainage (Butler, 1991). SAGD uses horizontal wells to maximize the effect gravity (Butler, 1998). In the idealized SAGD process, a growing steam chamber forms around the horizontal injector and steam flows continuously to the perimeter of the chamber where it heats the surrounding oil. Effective initial heating of the cold oil is important for the formation of the steam chamber in gravity drain- age processes (Edmunds and Gittins, 1993; Elliot and Kovscek, 2001). The heated oil drains to a horizontal production well located at the base of the reservoir just below the injection well. Butler (1991) derived Eqs. (1a,b) 0920-4105/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.petrol.2004.04.006 * Corresponding author. Tel.: +1-650-723-1218; fax: +1-650- 725-2099. E-mail address: kovscek@pangea.stanford.edu (A.R. Kovscek). www.elsevier.com/locate/petrol Journal of Petroleum Science and Engineering 45 (2004) 83 – 96