Numerical Simulation of the SAGD Process In the Hangingstone Oil Sands Reservoir

Abstract

This paper presents a simulation study of a steam. assisted gravity drainage (SAGD) process applied to the Hangingstone tar sands reservoir. Two pairs of 500 m long horizontal wells installed from the surface are considered. The study was conducted to forecast recovery performance and to further understand the oil production mechanism. Results predicted that more than 60% of the oil can be produced in six years of operation with a steam-oil ratio of less than 3.0. The study was extended to provide a visual understanding of the flow behaviour of steam, oil, and water in the reservoir. The fluid flow diagrams revealed that oil is displaced mainly by steam condensate and that convective energy carried by steam condensate dominates the heat transfer mechanism. The authors applied this recovery mechanism concept to the study of subcooling temperature optimization for the steam trap control. The results of this reservoir dynamics study are presented. Finally the role of this process's geomechanical effects are briefly discussed. Introduction The Hangingstone oil sands reservoir is located near Fort McMurray. The reservoir is jointly owned by Petro-Canada, Imperial Oil, Canadian Occidental, and Japan Canada Oil Sands (JACOS). The bitumen viscosity at reservoir condition is over 1,000,000 mPa.s and will not flow naturally. JACOS is going to use a Steam Assisted Gravity Drainage (SAGD) process to extract bitumen from the Hangingstone reservoir. A cyclic steam stimulation (CSS) process was extensively tested for the same reservoir over a decade. Through a numerical simulation study of the performance, it was found that the bitumen is difficult to produce at economically feasible rates using the CSS process for the subject reservoir(1). After seven cycles of CSS operation, 3,182 m3 of oil was produced for a total of 28,000 m3 of steam injection. Steam oil ratio and calendar day oil rates were 8.8 and 3.45 m3/day respectively. JACOS has been participating in the Underground Test Facility (UTF) project since 1991 when Phase A of the project was completed. From its participation, JACOS has received all of the field data plus operating and drilling experience. UTF's field data have been extensively analysed through numerical simulation. Based on the analysis of the data, it was decided to drill two pairs of 500 m horizontal wells in 1997 and to start operating the SAGD process in 1998. The expected well performance calculated using a thermal simulator is presented in the paper. Following the base case run, a series of parametric studies were conducted. Some interesting results, such as the oil recovery mechanism obtained from the study, are also included. Although many uncertainties still exist in both the recovery concept and operational procedure for the SAGD process, promising potential for its application has been demonstrated in Phases A and B of theUTF project(2, 3). One major uncertainty is whether the geomechanical change of the formation during the process is an important aspect or not. The role of geomechanical effect in the growth of the steam chamber and well performance is also presented.

Effect of Oil-Viscosity-Gradient Presence on SAGD

“…Oil-Viscosity Gradient Uniform Oil Viscosity Ito and Suzuki 1999). Local steam-trap control is one of the effective approaches to resolve the problem related to uneven steam-chamber development along the full length of the SAGD well pair; however, this strategy is valid only in the simulation study, at least at this stage.…”

“…When the temperature of the producing fl uid becomes too hot, then production rates are reduced to lower the steam fl ow into the production well. According to Ito and Suzuki (1999), the temperature of the fl uid draining along the side of the steam chamber is approximately 30 to 40°C colder than the steam-saturation temperature. If the steam-trap temperature is set less than this temperature (e.g., 20°C), direct steam fl ow to the production well provides a match to the desired production temperature of 20°C.…”

A Critical Review of the Status of SAGD: Where Are We and What Is Next?

“…Without showing production results, they concluded feasibility of SAGD application. Ito and Suzuki (1996) observed a large amount of oil drains through steam chamber when geomechanical changes occur in the reservoir. They hence flagged the role of geomechanical change of formation during SAGD as very important.…”

“…He then added that in the field due to the uneven nature of the well trajectory, it is very difficult to identify, rest alone, and control steam breakthrough. Ito and Suzuki (1996) reported an optimum temperature for a steam trap control to be between 30 to 40 o C. They referred that to fluid drainage ahead of steam chamber is 30 to 40 o C lower than steam saturation temperature. Das (2005) noticed a positive effect of sub cool temperature after exceeding 20 o C. Chen et al (2007) showed that when coupling hydraulic fracturing with steam trap control of the producer well, injectivity is dramatically improved and an effective oil production rate in the reservoir with poor vertical communication is achieved.…”

Artificial Lift-A Major Unresolved Issue for SAGD

“…Ito and Suzuki (5) studied steam-trap control with a simple two-dimensional (2D) grid system, and a drawdown into the production well of less than 40 kPa. They found that the optimum subcool values were between 30˚ C and 40˚ C. They also noted that the subcool value should be corrected for higher drawdowns which were observed at the UTF pilot.…”