Sub-Cool, Fluid Productivity, and Liquid Level Above a SAGD Producer
- Jian-yang Yuan (Osum Oil Sands Corp) | Daniel Nugent (Osum Oil Sands Corp)
- Document ID
- Society of Petroleum Engineers
- SPE Heavy Oil Conference Canada, 12-14 June, Calgary, Alberta, Canada
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 1.2 Wellbore Design, 5.1.1 Exploration, Development, Structural Geology, 5.2.1 Phase Behavior and PVT Measurements, 5.5 Reservoir Simulation, 5.3.9 Steam Assisted Gravity Drainage
- 2 in the last 30 days
- 363 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 8.50|
|SPE Non-Member Price:||USD 25.00|
Thermodynamic steam trap, or sub-cool control, in a typical SAGD production is essential to the stability and longevity of the operation. It is commonly achieved through the control of fluid production. The goal of such control is to maintain a steady and healthy liquid production without allowing bypassing of steam from the injector to the producer. Therefore, it is effectively a control of the liquid level above the producer. Unfortunately, it is not practical to monitor this liquid level. A rule of thumb sub-cool estimation of 10°C/m of liquid level is popularized in the industry, however, does not prove to hold in many situations.
This paper presents a study of the dynamics of SAGD production control with a resulting algebraic equation that relates sub-cool, fluid productivity and wellbore draw down to the liquid level above a producer. The main conclusions of this study include:
a. There is no minimum sub-cool value for a pure gravity drainage scenario; however, as the wellbore draw down is considered there is minimum sub-cool value in order to maintain the stability of fluid flow.
b. For a given productivity, the liquid level increases as sub-cool increases or as wellbore draw down decreases.
c. For each set of parameters, there exists a minimum productivity below which SAGD operation would halt.
d. Before the steam chamber reaches the top of the reservoir, the production rate is limited by the vertical distance between the injector and the producer, the larger the distance the higher the production rate can be.
A verification of this analysis was conducted via a series of numerical reservoir simulations. Although limited to 2D, we believe this analysis captures the main physics amid the dynamic complexity of SAGD production control. The resulting algebraic equation can be used for better understanding the dynamics of sub-cool control and determining operation strategies.
The necessity and the operation principle of sub-cool control, also termed as steam trap control in SAGD operations have been well described and discussed by Edmunds . Apparently, there must be a domain of operation conditions within which "the steam chamber be kept well drained, so that liquid does not accumulate over the producer but either is steam produced.?? Many studies have been conducted [2-6] relating sub-cool control with optimization of SAGD.
It is known that the liquid level above the production well is related to the pressure difference, the sub-cool and production rate. A rule of thumb estimation of 10°C per metre of liquid level has established its popularity in the industry although it is not always proven correct. It is clear that the relationship between the sub-cool and the liquid level could not be determined by thermal equilibrium. For example, at 3MPa steam chamber pressure, according the steam table, 1°C of sub-cool would lead to a hydraulic head of 6.8 metres. Therefore, this relationship must be strongly dynamic. If such a dynamic relationship is well understood, we would have a much better confidence in operation condition controls, including sub-cool control. This would definitely help optimization of SAGD operations. This was our motivation of tackling this issue.
|File Size||1 MB||Number of Pages||13|