Canada’s oil sands are one of the world’s largest
hydrocarbon resources. The initial volume of crude bitumen in place is
estimated to be approximately 260 billion cubic metres with 11 percent or 28
billion cubic metres recoverable under current economic conditions. Continually
improving economics, bolstered by recent higher crude oil prices, has resulted
in the International recognition of the vast potential of Canada’s oil
sands. Based on publicly announced development plans through to 2015, over C$60
billion could be invested in numerous projects to develop the oil sands.
Various factors have to be considered to select the proper cement for
zonal isolation of thermal recovery heavy-oil wells. First the cement should be
flexible enough to withstand the stresses which occur when casing expands
during the heating up of the well. To reduce these stresses, the cement thermal
expansion coefficient should be similar to the thermal expansion coefficient of
the casing. Finally, cement mechanical properties should not degrade during the
whole steam injection process, i.e. when it is subjected to extremely high
temperatures (up to 350 degC) for extended periods of time.
Specifically in Canada, the majority of the steam injection wells are
drilled in shallow sandstone formations. This requires the cement to have high
flexibility to resist the stresses. Moreover, during steam injection, a
reaction between the sandstone formation and the cement sheath may occur,
impacting the cement matrix and hence changing its properties.
This paper describes the application of a new thermally responsive
cement for zonal isolation of heavy oil wells in Canada. This system is
designed to have excellent strength, flexibility and thermal properties even
upon interaction with sandstone formations. It minimizes the mechanical
stresses exerted on the cement sheath during steam injection, thus reducing the
risk of loss of well integrity. The numerical simulations performed with these
long-term material properties (six months of exposure to 350 degC) for typical
Canadian heavy oil wells conditions predict reliable and durable zonal
isolation under these extreme conditions. These simulation results are
confirmed by several field applications in wells which have not leaked after
months of steam injection.
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