Abstract
In 2007, work was published on the predictability of hydrogen sulphide
production in Athabasca SAGD projects. It was possible to predict the hydrogen
sulphide production per unit volume of bitumen produced against steam zone
temperature, by assuming pseudo-zero order kinetics, using the Arrhenius energy
published by Strausz and his co-workers at the University of Alberta.
An examination of field results for carbon dioxide production in Athabasca
projects shows that the predictability of carbon dioxide is less simple. The
carbon dioxide production is not erratic but goes through a distinct
temperature minimum, an important result in view of the dependence of silica
production in SAGD and scaling behaviour in facilities on carbon dioxide.
Again, as for hydrogen sulphide production, it is possible to estimate carbon
dioxide production by a simple graphical technique, which is shown.
Partial explanations for the observed temperature minimum are offered.
Introduction
The production of acid gases in SAGD projects is a matter of some
importance. A number of operational characteristics depend on the presence of
carbon dioxide as produced through dissolution in produced water. It has been
shown previously(1) that silica production is strongly dependent on dissolved
carbon dioxide. There is likewise evidence that aggressive degassing of
produced water has caused unwanted scales of silicate minerals, such as talc,
chrysotile and tremolite, to be deposited in various parts of the
facilities(2).
A simple production diagram for hydrogen sulphide in SAGD was recently
reported by Thimm(3). The hydrogen sulphide produced per unit bitumen could be
described as a simple Arrheniustype relationship with steam zone temperature,
using an activation energy of 56,220 – 65,920 J/mole (13,450 – 15,770
cal/mole). The assumption of pseudo-zero order kinetics yielded a smooth curve
which fitted the field data for most SAGD projects in Athabasca
satisfactorily.
The behaviour for carbon dioxide was previously expected to be similar, with
an Arrhenius activation energy of 17,520 J/mole (4,192 cal/mole)(4).
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
24 March 2008
- Meeting paper published:
17 June 2008
- Revised manuscript received:
14 August 2009
- Manuscript approved:
15 September 2009
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