Summary
Heavy-oil production is one of the new challenges the oil and gas industry
faces today, with trillions of barrels of reserves around the planet. To
extract heavy oils, the viscosity has to be reduced to gain mobility and start
the oil flowing. Of all the possible techniques, steam stimulation is, today,
the most promising.
Steam is injected through the well down to the reservoir to warm it to a
temperature of up to 250°C, inducing extreme thermal stresses in the well
(especially when the temperature gradient through its components is maximum, as
it is during initial steam injection or during workover when the well has to be
quickly cooled down and heated up again to restart production rapidly).
To avoid zonal-isolation failure and steam release at the surface, new rules
need to be considered in designing the barriers of a well exposed to steam
stimulation, especially in very shallow fields. Where conventional rules may be
applied for casing design, pioneering rules should be considered for designing
the cement sheath.
This paper presents an innovative methodology for designing robust cement
sheaths in very shallow conditions. First, stresses in the field are assessed
with a rock-mechanics simulation. Then, the thermal gradient in the well
components during the heating process is evaluated with a thermal simulation of
the well. Both results are entered into Total’s dedicated software to determine
the mechanical properties the cement should have to withstand the thermal
stresses. Different cement systems from service companies are evaluated in a
cell, reproducing the field conditions to validate the simulation results.
This methodology was applied successfully to the Joslyn field wells, in
Canada, where a resilient cement system with low Young's modulus and high
tensile strength was selected and pumped. Because the results were positive,
the methodology has been extended to other Total fields around the world where
steam simulation is being considered.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
22 August 2008
- Meeting paper published:
20 October 2008
- Revised manuscript received:
10 April 2009
- Manuscript approved:
22 April 2009
- Published online:
14 January 2010
- Version of record:
11 March 2010
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