Foamy oil flow in heavy oil–solvent systems tested by pressure depletion in a sandpack Xiang Zhou a , Fanhua Zeng a,⇑ , Liehui Zhang b , Hongyang Wang a a Petroleum Systems Engineering, Faculty of Engineering and Applied Science, University of Regina, Regina, Saskatchewan S4S 0A2, Canada b State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, PR China highlights  Foamy oil behaviors for three heavy oil–solvent systems were studied.  The three systems are heavy oil with methane, propane and mixture, respectively.  Effects of pressure depletion rates on each system were studied.  Optimum pressure depletion rates were obtained for each system. article info Article history: Received 26 September 2015 Received in revised form 13 December 2015 Accepted 29 December 2015 Available online 4 January 2016 Keywords: Foamy oil flow Heavy oil–solvent systems Pressure depletion rate Critical foamy oil flowing pressure Experimental study abstract In this study, pressure depletion tests on foamy oil flow were conducted in a one-meter-long sandpack system to investigate the effect of pressure depletion rates on different heavy oil–solvent systems in por- ous media. Pure methane, pure propane, and a mixture of methane and propane were recombined respectively into a typical Manatokan dead heavy oil sample to generate live oil samples, four different pressure depletion rates were undertaken for each heavy oil–solvent system. The experimental results showed that, a critical pressure depletion rate, at which the maximum oil recovery factor (RF) could be obtained, was observed for each heavy oil–solvent system. The critical pres- sure depletion rates were 1.70 kPa/min, 0.76 kPa/min, and 3.97 kPa/min with the oil RF of 22.13%, 24.17%, and 21.80%, for heavy oil–methane, heavy oil–propane, and heavy oil–mixture systems, respectively. The foamy oil for heavy oil–methane system is more stable than heavy oil–propane system due to (1) that for heavy oil–methane system, significant amount of oil were produced after the pressure in the back pres- sure regulator (BPR) dropped to atmosphere pressure and (2) that for heavy oil–propane system, the pressure plots show many pressure fluctuations due to the high solubility of propane and non-stability of gas bubbles in the foamy oil. For heavy oil–mixture system, the foamy oil flow behavior is more com- plex than heavy oil–pure solvent systems and it is suggested that the performance of foamy oil flow of heavy oil–mixture system is poorer than heavy oil–methane and heavy oil–propane systems, which might be caused by non-homogenous bubbles generated by the mixture of methane and propane. The results obtained in this study could be used to guide cyclic solvent injection (CSI) design in field. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction The terminology ‘‘foamy oil” is widely applied to describe the dispersed gas–liquid two-phase fluid, which presented from heavy oil reservoirs under solution gas drive in western Canada, Vene- zuela, China, and Oman [1–7]. Compared the production perfor- mance with conventional heavy oil reservoirs, anomalous oil production behaviors, in terms of high oil production rate, low gas oil ratio (GOR), and high recovery factor (RF), were observed in the heavy oil reservoirs under solution gas drive [3,8–15]. Specifically, the oil production rates from these reservoirs were as 10 to 100 times [4,16], even 300 times [17] as that predicted using Darcy’s law without considering foamy oil flow behaviors. Numerous experimental [2,6,8,15,18,19], theoretical [3,7,11,13, 20–22], and field [9,16,23] studies have been conducted to study the mechanisms of the anomalously high primary oil RF in heavy oil reservoir under solution gas drive. One of the key mechanisms to the high oil RF is due to the properties of the reservoir fluids in the pressure depletion process [1,24], in which foamy oil was http://dx.doi.org/10.1016/j.fuel.2015.12.070 0016-2361/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +1 306 337 2526; fax: +1 306 585 4855. E-mail address: fanhua.zeng@uregina.ca (F. Zeng). Fuel 171 (2016) 210–223 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel