1
2
3
PETROSTAB : Thermal stability of hydrocarbons
in geological reservoir – Coupling reaction
kinetics and transport in porous media
Irina PANFILOVA3, Roda BOUNACEUR2, Valérie BURKLÉ-VITZTHUM2, Paul-Marie MARQUAIRE2,
1
1,2
3
3
Raymond MICHELS , Nguyen VAN PHUC , Marion SERRES , Jamilyam ISMAILOVA
Socio-economics
Table 1 : Reduced chemical reaction mechanism
Exploration and analysis of unconventional oil deposits require new tools
of modelling which are capable to help in understanding the nature and the
hydrocarbon fluids of the geological reservoirs. Compositions and
properties of these fluids are inherited from the geological history of
deposits (cracking in conditions of time, geological temperature, pressure),
but also influenced by technologies of production (cracking in conditions of
steam injection). To understand the behaviour of complex hydrocarbon
fluids in the oil deposits it is necessary to combine the different disciplines:
geo-sciences, chemical kinetics, fluid mechanics, transport in porous
media. This project integrates these competences and has as objective to
develop an experimental study which allows building a reactive model of
thermal stability of hydrocarbons extrapolable to the conditions of
geological reservoirs.
Primary mechanism, k1, Ea1
Secondary mechanism, k2, Ea2
C8H18
C8H18
C8H18
C8H18
C8H18
C8H18
C8H18
C8H18
C8H18
C8H18
C8H18
C8H18
=>C2H4+C6H14
=>C3H6+C5H12
=>C4H8+C4H10
=>C5H10+C3H8
=>C6H12+C2H6
=>C7H14+CH4
+C2H4=>C10H22
+C3H6=>C11H24
+C4H8=>C12H26
+C5H10=>C13H28
+C6H12=>C14H30
+C7H14=>C15H32
Fig.2. Appearing
of lightest fluid
below
the
heavier due to
the composition
change in the
bottom.
Axe Ressources
Scientific and Technological Issues
The oil industry has need of modeling tools to understand the nature and
distribution of hydrocarbon fluids in geological reservoirs to estimate prior
to drilling, the quality of potential reserves, to scale or optimize
production. The properties of these fluids are either inherited from the
geological history of the deposits (T <200 ° C, time of several million
years) or conditioned by the parameters of enhanced recovery (T> 300 °
C, a few years time ). In all cases, we must be able to reconstruct the
reaction schemes and transport of hydrocarbons in geological conditions.
These aspects are even more critical on unconventional targets: very
deep and hot reservoirs, sulfur rich reservoirs, acidic gas (H2S) injection
in depleted petroleum reservoirs, enhanced recovery by steam injection.
Figure 1: oil migration
pathways
in
porous
rocks. From souce-rock
into carrier beds and trap
Methodology
In this work we consider the migration pathways of hydrocarbons to
the gas/oil deposits. Under high temperature oil changes composition
at all stages: in the source rocks, then during the migration in pathway
through the micro fractures or porous facies and finally in the
geological trap, Fig.1. The main driving force for migration of
hydrocarbons is buoyancy. If the densities of the hydrocarbon phase
and the water are known, then the magnitude of the buoyant force
can be determined for any hydrocarbon column. The main resistant
force to hydrocarbon migration is the capillary pressure. Thus
knowing the composition of hydrocarbon phases can help to
understand the migration mechanism and the resulting composition in
the gas/oil reservoir.
The process of thermal oil cracking involves a complex reaction
network. To describe as simply as possible the reactive mechanism
and to couple it with the multi-component hydrodynamic transport we
use a reduced formulation of octane cracking, which contains primary
and secondary mechanisms, Table 1. The reaction rate (k) and
activation energy (Ea) for each mechanism are given from the
Chemkin® simulation.
Fig.3. Molar density
for three cases of
diffusivity: (A) low; (B)
moderate; (C) high.
Results
Static simulation
The static simulation corresponds to the constant temperature in the
source-rock or the reservoir (250°C). The comparison of the simulations
with ECLIPSE and CHEMKIN shows 1) a change in chemical
composition with the formation of light hydrocarbons especially 2)
increase in pressure 3) heterogeneity in the fluid by density segregation.
Dynamic modelling
In the dynamic modelling the constant source of octane is attributed to
the bottom of reservoir. The model is one-phase liquid system. The
competition between three processes is observed: convection flow,
diffusion and chemical reactivity.
For the low diffusivity case the major changes in the composition due to
the octane cracking occurs at the bottom. It leads to the reduction of oil
density and appears as the lightest oil below the heavier. This situation
is described by the instability of Rayleigh–Bénard, fig.2, when the
natural convection occurs in a plane horizontal layer of fluid heated from
below, in which the fluid develops a regular pattern.
In the case of high diffusion between the components in comparison
with the chemical reactivity and the convection transport, fig.3C, the
light components are mixed rapidly in the oil and the system becomes
homogeneous without difference in the densities fig. 3A. So the
instability of Rayleigh–Benard is not observed anymore, fig.3C.
Outcome – Developement Perspectives
The project allowed to set the first steps in the construction of a
transport-reaction model dedicated to hydrocarbons behaviour in
geological conditions. New developments have been achieved and
conducted to presentations in international meetings as well as
publications.
Nguyen V. P., Michels R., Marquaire P.-M., Burklé-Vitzthum V. (2012) 19th International Symposium on Analytical
and Applied Pyrolysis. 21-25th May. Linz, Austria.
Nguyen V. P., Burkle-vitzthum V., Michels R., Marquaire P. M. (2013). 26th International Meeting on Organic
Geochemistry, Tenerife (Spain), 16-20 Sept.
Nguyen V. P., Burkle-vitzthum V., Michels R., Marquaire P. M. (2014). 20th Internaional Meeting on Analytical and
Applied Pyrolysis, Birmingham, UK, 19-23 May 2014.
Nguyen V.P., Burkle-vitzthum V., Marquaire P.M., Michels R. (2013). Jour. An. Appl. Pyr., 103, 307–319
Ateliers Scientifiques - 27 mai 2014