T.R. Ibatullin, T. Yang, E.B. Petersen, M. Chan, O. Rismyhr, S. Tollefsen,
Thermal recovery processes are widely applied for heavy oil and bitumen
production. Unique thermal properties of water and water steam allowed
efficient reduction of extremely high viscosities by several orders of
magnitude and made a vast heavy oil and bitumen reserves production technically
and economically feasible.
Steam effect on heavy oil and bitumen in traditional reservoir engineering for
a long time has been considered as physical only, i.e. viscosity reduction,
improved flow parameters, distillation effects, emulsification, etc. However
multiple laboratory studies and field observations suggest that initial oil
undergoes chemical alteration and gases such as H2S and CO2 could be produced
in increased quantities. Estimation of H2S and CO2 production potential is
important due to considerable corrosivity of these gases, associated
environmental, economical and other issues.
In this study a practical approach has been developed to simulate and forecast
H2S and CO2 production during thermal recovery using common reservoir
simulation tools. First, analytical data was matched and then chemical reaction
had been implemented to the sector model. Steam Assisted Gravity Drainage
(SAGD) was chosen to demonstrate the concept of suggested approach and analyze
Generated gases were considered to be soluble both in water and oil. The
importance of accounting for gas solubility in water was demonstrated and
discussed. Simulated volumes of H2S and CO2 are in good agreement with that
observed in the field applications of steam assisted recovery methods.
Thermal recovery is one of the most extensively used processes for heavy oil
and bitumen production. Majority of ongoing thermal recovery projects involve
either steam or hot water injection due to their unique thermal properties.
Unparallel latent heat of condensation and heat capacity make water a very
efficient mean of energy delivery into the reservoir.
Heat propagation in the reservoir results in rapid oil viscosity decrease
(often by several orders of magnitude) and subsequent improvement of reservoir
flow characteristics. Along with viscosity reduction multiple physical effects
such as distillation, emulsification, interfacial tension change, etc. could
A number of laboratory experiments1-16 and analysis of production data1,17-19
indicate that steam assisted recovery can induce complex chemical interactions
between water, oil and reservoir rock. Such gases as H2S and CO2 are often
among the products of reactions along with CH4 and light
Aquathermolysis and decarboxylation are two primary mechanisms of H2S and CO2
generation in the temperature range of 200-300°C4,6,14. As steam temperature
approaches 300°C thermal cracking of different oil compounds becomes
increasingly important process and contributes considerably into the overall
gas generation4-6,22. In this paper H2S and CO2 generation issue will be of