Thermodynamic steam-trap control, or subcool control, in a typical steam-assisted gravity-drainage (SAGD) production is essential to the stability and longevity of the operation. It is achieved commonly through the control of fluid production. The goal of such control is to maintain a steady and healthy liquid production without allowing steam from the injector to bypass 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 subcool-per-metre estimation of 10 C/m of liquid level is popular in the industry; however it 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 subcool, fluid productivity, and wellbore drawdown to the liquid level above a producer. The main conclusions of this study include There is no minimum subcool value for a pure-gravity-drainage scenario; however, as the wellbore drawdown is considered, there is a minimum subcool value in order to maintain the stability of fluid flow.For a given productivity, the liquid level increases as subcool increases or as wellbore drawdown decreases.For each given set of operating parameters, there exists a critical productivity below which SAGD operation would halt.Before the steam chamber reaches the top of the reservoir, the fluid productivity is limited by the vertical distance between the injector and the producer; the larger the distance, the higher the fluidproduction rate can be.A verification of this analysis was conducted by a series of numerical reservoir simulations. Although limited to two dimensions, we expect that this analysis captures the main physics amid the dynamic complexity of SAGD-production control. The resulting algebraic equation can be used for better understanding of the dynamics of subcool control and for determining operation strategies.

Bitumen saturated carbonates of the Grosmont C member of the Grosmont Formation in the Saleski area are intensely fractured. The fractures connect the vuggy porosity and are the reason for in situ permeabilities that exceed 10 D. These carbonate rocks are more hydrophobic with high bitumen saturations. Most existing pilot data suggest the reservoir is in general "leaky" in comparison with siliclastics, such as the McMurray or Clearwater Formations. Furthermore, it is also observed that during CSS operations, especially in the earlier cycles, oil cuts are initially high and decrease with time. This character differs from CSS in siliclastics where initial oil cuts are low and increase with time. To fully understand these observed phenomena, we believe that common knowledge gained in studying siliclastics may not be enough. Geological studies have indicated that the Grosmont carbonate fracture system may not be a well-defined dual scale fracture-matrix system. It may be better defined with a multiple scale system. Geological models using the concept of fractals having selfsimilarity and fractional dimension have been proposed by Wagner et al.. In this presentation, we further postulate that the fractal nature of the Grosmont carbonates offers explanations to the above-mentioned observations. Using the published data of pilot tests in Grosmont, we demonstrate that it is possible to attribute "the loss of pressure" to very large total contact areas between fractures/vugs and the rock matrix in a fractal system, although the matrix permeability can be very low. The high oil cuts were interpreted as the result of considering high permeability channels with significant volume. Numerical simulations confirmed these assertions. This fractal point of view sheds some lights on our journey of eventually understanding and mastering the fluid flow behaviours in Grosmont carbonates.

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: 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.For a given productivity, the liquid level increases as sub-cool increases or as wellbore draw down decreases.For each set of parameters, there exists a minimum productivity below which SAGD operation would halt.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 southwest portion of the proposed Taiga project has two vertically stacked bitumen-filled Cretaceous sandstone reservoirs in the Cold Lake area of NW Alberta, Canada. The shallower Lower Grand Rapids Formation is separated from the Clearwater Formation by the transgressive Clearwater. SAGD (steam assisted gravity drainage) is planned for producing both formations simultaneously. The Lower Grand Rapids Formation differs from the Clearwater Formation in initial reservoir pressure, oil viscosity and fluid distribution. Therefore, this will require individual well placement and operational strategies for each reservoir. The sequence of development for the two reservoirs will not only affect the pad facility design and operation strategy but will also affect the drilling operations. There is a high likelihood of drilling into the areas conductively heated by prior proximal SAGD operations if two formations are developed in a sequential order. This increases drilling risks and costs. Simultaneous SAGD operations within both the Lower Grand Rapids and Clearwater Formations can be used to minimize the complexities associated with well drilling and completions, and to reduce the initial number of surface pads as both formations can be accessed from the wells drilled from the same surface location. This paper presents the results from both reservoir simulation and geo-mechanical modeling based on geological and reservoir characteristics of these reservoirs. The surface heave due to dual zone thermal operations is also predicted based on the results from geo-mechanical modeling. These studies have led to an optimal design of pads and operating parameters for concurrent production of the two reservoirs which is technically, environmentally and economically efficient.