Full Length Article Improving Steam-Assisted Gravity Drainage performance in oil sands with a top water zone using polymer injection and the fishbone well pattern Xiang Zhou a , Fanhua Zeng a,⇑ , Liehui Zhang b 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 article info Article history: Received 8 April 2016 Received in revised form 8 July 2016 Accepted 12 July 2016 Available online 18 July 2016 Keywords: Simulation study Steam-Assisted Gravity Drainage (SAGD) Fishbone well pattern Top water zone Polymer solution abstract In western Canada, a significant number of oil sands reserves have little or no cap rock with a top water zone. Due to huge heat loss to the top water zone, the conventional Steam-Assisted Gravity Drainage (SAGD) process is uneconomical when applied directly in this type of reservoir. In this study, it is proposed that a high temperature polymer solution can be injected into the bottom of the top water zone to establish a stable high viscosity layer that will prevent steam from leaking into the top water zone. In order to select a suitable polymer that has stable viscosity under high temperature, the viscosities of different polymer solutions at different temperatures were measured and the concentration of the selected polymer solution was optimized. Furthermore, in order to extend the connection area between the oil sands and the steam chamber, the fishbone well pattern was applied instead of the single well pair pattern. Numerical simulations were performed to evaluate the feasibility of using the selected polymer in the fishbone well pattern to improve SAGD performance in oil sands with a top water zone. The numerical simulation model was based on a typical Athabasca oil sands reservoir. In this study, the effects of steam injection pressure, polymer solution injection time, steam injection rate, and different fishbone well pat- terns on the performance of the SAGD process were studied and optimized. The numerical simulation results suggest that the fishbone well pattern could extend the steam distri- bution and that polymer injection is able to prevent heat from leaking into the top water zone. Compared to the conventional SAGD process in an oil sands reservoir with a top water zone, the optimal case using a one-fishbone well pattern and polymer injection could enhance the oil production significantly. Under these conditions, the oil recovery factor in this study increased from 10.58% to 59.02%; the cumulative steam oil ratio decreased from 10.44 m 3 /m 3 to 3.85 m 3 /m 3 ; and the cumulative injected energy oil ratio decreased from 24.00 GJ/m 3 to 8.87 GJ/m 3 . This indicates that the SAGD process with the one-fishbone well pattern and polymer injection is able to improve SAGD performance in oil sands with a top water zone. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction The production potential of heavy oil and bitumen in Alberta, Canada, is high [1]. The original heavy oil/bitumen in place is 1.7 trillion barrels [2–4]. A significant amount of this oil/bitumen is contained in reservoirs with a top water zone, for instance, reser- voirs in Surmont leases, Kearl Lake and Wabiskaw-McMurray deposit [5–8]. The SAGD process has been approved as a leading technology for the in-situ recovery of heavy oil and bitumen [9–12]. However, the efficiency of the SAGD process for reservoirs with a top water zone is too low to make this process economical. The reason for this is that the existence of a top water zone can result in signifi- cant water influx into the steam chamber [13] and tremendous heat loss from the steam chamber into the top water zone, such that it significantly reduces the thermal efficiency. Some experimental and numerical simulation studies have been conducted to analyze fluid flow behaviors and study the rela- tionship of the oil recovery factor (RF) and heat loss for reservoirs with a top water zone. Nasr et al. conducted 3-D laboratory http://dx.doi.org/10.1016/j.fuel.2016.07.040 0016-2361/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: fanhua.zeng@uregina.ca (F. Zeng). Fuel 184 (2016) 449–465 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel