25th International Meeting on Organic Geochemistry IMOG 2011

O-71
Aquathermolysis: pressure effect on gas production and oil
composition
Violaine Lamoureux-Var, Françoise Behar
IFP Energies Nouvelles, Rueil-Malmaison, France (corresponding author:violaine.lamoureux-var@ifpen.fr)
Steam injection is one of the main thermal production
processes for enhancing oil recovery in petroleum
reservoirs. This process induces gas generation and
oil composition modification, resulting from
physicochemical transformations in the reservoir
called aquathermolysis. Until now, little attention has
been given to the possible influence of steam
pressure and/or water phase on gas generation and
oil composition. To address this issue,
aquathermolysis laboratory experiments were carried
out under various pressures, on an oil sand sample
with added distilled and free-oxygen water (1/1,(v/v)),
at 250°C/1 month in sealed gold tubes. The applied
external pressure was constant, in the range from 40
to 120 bar, enabling the water to be either in vapour
phase (40 bar), or in liquid phase (120 bar) or in a
coexisting liquid/vapour phase. At the end of the
experiments, the total gas was recovered and
quantified in absolute amounts. For some
experiments, mass balance on the liquid products
was done on the C14+ hydrocarbons, the resins and
asphaltenes.
Gas results show clearly that both CO2 and H2
absolute yields decrease between 40 and 60 bar and
then increase between 60 and 80 bar (Fig. 1).
Although H2S was difficult to quantify, the H2S/H2
molar yields ratio evolves clearly: it increases from 40
to 60 bar and then decreases from 60 bar to 80 bar
(Fig. 1).
The presence of hydrocarbon gases reveals some oil
cracking. The C1/ C2-C4 molar yields ratio appears to
decrease from 40 to 60 bar, indicating the production
of a wetter gas as pressure increases, and then
seems to remain constant. Moreover, it is observed
an increase of isomerisation for the butane
compounds below 60 bar, since the ratio iC4/n-C4
increases from 40 to 60 bar.
All these results suggest that the pressure has a
strong impact on the oil sand reactivity under
aquathermolysis experiments. So far, two factors may
be responsible to these observed data: either the
pressure and/or the water phase. In order to
distinguish the possible causes, complementary work
is in progress, in particular by running the same set of
experiments without water.
CO2 yield (µg CO2/g oil
sand)
H2S/H2 (mol/mol)
2000
1800
1600
1400
1200
1000
800
600
400
200
0
18
16
14
12
10
8
6
4
2
0
CO2
vapour
water water
phase
transition
liquid
water
30 35 40 45 50 55 60 65 70 75 80 85
Pressure (bar)
vapour
water
H2S / H2
water
phase
transition
30 35 40 45 50 55 60 65 70 75 80 85
Pressure (bar)
liquid
water
Aquathermolysis experiments conducted on an oil sand
sample, at 250°C, during 1 month, for different pressures
from 40 bar to 80 bar. Upper: CO2 absolute yield. Lower:
H2S/H2 absolute molar yields ratio.
Figure 1: Pressure effect on non-hydrocarbon gases
generation during aquathermolysis.
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