Steam stimulation of the Cold Lake bitumen reservoir causes fracturing of the formation. Steam enters via convection along the fracture plane, and heat propagates perpendicular to this plane by conduction, which in some cases may be enhanced by convection. Temperature profiles from observation wells located around stimulated wells directly give the energy distribution at those locations. The analysis can be extended beyond energy distribution by distinguishing regions of convective and conductive heat transfer in the temperature profiles. Simple analytical models can then yield important insights into the cyclic steam stimulation process, such as fracture geometry and fluid flow velocity. Eight field cases are discussed representing profiles from the injection, shut-in, and production phases of the process.
The Cold Lake oil sands deposit is a major accumulation of bitumen of Cretaceous age, located 300 km northeast of Edmonton, Alberta. Approximately 25 billion cubic metres of bitumen is buried at depths ranging from 300 to 600 m. In the last two decades, commercial in situ steam stimulation recovery techniques have been developed by Esso Resources Canada Limited via several experimental pilots. Pilot operations have been previously summarized.
The recovery of the bitumen from the Cold Lake deposits faces three major challenges: high bitumen viscosity, low reservoir injectivity, and low reservoir energy. The bitumen's viscosity is highly dependent on temperature, and by steam injection it can be lowered to low values with an energy expenditure that represents only a small fraction of the energy content of the formation at typical bitumen saturations. But the low injectivity necessitates fracturing of the formation in order that commercial rates of steam injection can be achieved. The energy distribution and bitumen depletion will follow the fracture trends, and conformance problems can be anticipated. Even with a lowered viscosity, movement of the bitumen to the wellbore can be difficult because of the low reservoir energy; in fact, some of the proposed recovery processes for the Cold Lake sands assume that gravity is the predominant driving force.
The evolution of understanding in steam stimulation techniques has been essentially empirical. Alternative operating procedures such as perforating depth - have been tested via pilot operations. More than 50 observation wells have played an important role in the evaluations of pilot performance. This paper deals with the interpretation of the temperature profiles obtained from these observation wells.
Temperature observation wells are often placed in thermal pilots. The temperature profiles obtained directly represent the injected energy distribution at the well locations. Various thermal efficiency parameters can then be estimated, such as the percent energy remaining in the target interval. However, the percent energy remaining in the target interval. However, the interpretation of the temperature profiles from observation wells has not been directly addressed in the literature, but is referred to in the context of other deliberations.