Many bitumen reservoirs contain shale layers of varying thickness, lateral extent, and frequency. These shale layers sometimes severely reduce vertical permeability of the pay zone and tend to slow down the SAGD process by interfering with theflow of steam and oil. Therefore, to improve productivity in these reservoirs, identifying shale problems has become necessary and solutions are urgently needed.

In this study, numerical simulation was performed to assess the shale issues in SAGD process. CMG STARS was used as a simulator. Hypothetical shale cases were built in SAGDsimulation models. In these simulation models, a geostatistical model was used to generate interbedded shale distribution for typical Athabasca heterogeneity.

A set of numerical simulations was also run to determine the potential of pressure cycling as a method of enhancing reservoir permeability, and hence offsetting the negative effectsof shale barriers. The analysis showed that for a deep Athabasca reservoir, two pressure cycles to 10,000 kPa could enhance production in terms of cumulative oil and SOR. This was true for the 10% shale, 15% shale and 20% shale cases.

The severest case, 25% shale, did not show a productivity enhancement due to pressure induced dilation. The report concludes with recommendations for additional numerical simulation effort to examine the effects of thermal stress on thesand and shale geomechanics, where the effects of shale disruption are most likely to be represented.


SAGD is the main commercial technology used for in-situ recovery of bitumen from Athabasca oil sands. SAGD typically operates by injecting steam from the upper well of a pair of horizontal wells, and producing oil from the lower well of the well pair. The space occupied by the drained oil is filled with steam, creating a vapour chamber.

Many bitumen reservoirs contain shale inclusions of varying thickness, lateral extent, and frequency. These shale inclusions will tend to slow down the SAGD process by interfering with the flow of steam and oil.

The problem created by inter-bedded shale can be defined in several ways:

Shale, if of limited lateral extent, can slow down the flow of oil draining to the production well, and act as a reduced vertical permeability. There may be some concurrent reduction inhorizontal permeability as well.

The shale, if continuous over a significant lateral extent, can impede and re-route steam flow as well as oil flow. While conductive heat transfer can continue through the shales, the rerouting of steam may change the geometry of the vapour chamber, leading to reduced thermal efficiency of the SAGD process.

If shale intervals are sufficiently extensive, they can cut off the flow of oil from injector to producer. Such a situation may be remedied by orienting the well pair so as to intersect sloping shale, layers increasing the pressure so as to dilate the reservoir, using the heat and pressure from SAGD to disrupt shales, or using pressure cycles to encourage dilation that is not recovered.

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