2. TABLE OF CONTENTS
INTRODUCTION OF INSITU COMBUSTION
PROCESS AND TECHNIQUES INVOULED
CARBON ISOTOPE
CARBON ISOTOPE ANALYSIS
DIFFERENT CARBON ∂ VALUES
FIELD ANALYSIS AND INTERPRETATION
CONCLUSION
3. IN-SITU COMBUSTION
In-situ combustion is basically injection of an
oxidizing gas (air or oxygen-enriched air) to
generate heat by burning a portion of resident oil.
4. PROCESS DESCRIPTION
Most of the oil is driven toward the producers by
a combination of the following
Gasdrive (from the combustion gases)
Waterdrive
Based on the respective directions of front
propagation and air flow, the process can be
either of the following
Forward (when the combustion front advances in the
same direction as the air flow)
Reverse (when the front moves against the air flow)
6. CARBON ISOTOPES
Carbon (C) has 15 known isotopes, from 8C to 22C, of
which 12C and 13C are stable. The longest-lived radioisotope
is 14C, with a half-life of 5,700 years
Carbon has two stable isotopes, 12C(98.89%) and
13C(1.11%).
The accepted unit of isotopic measurement is the ∂ value
given in parts per thousand with the symbol °/00. The ∂13C
value in °/00
The international standard is called Pee Dee Belemnite PDB because it is based on a
belemnite sample taken from the Peedee formation of South Carolina.
7. Carbon isotope analysis
To determine the nature of reactions occurring during
the in-situ combustion process and to identify wells in
combustion communication.
Include the classic burning profile at the leading edge;
super-wet or low-temperature combustion; a wide
combustion zone with a secondary front, which is
indicative of oxygen channeling; and carbonate
decomposition in carbonate core
8. The carbon isotope study contributed to the
understanding of the origin and behavior of CO2 and
methane generated.
Carbon isotope data can assist in distinguishing the
type of fuel consumed and the nature of the reactions
occurring at the combustion front.
Carbon isotope measurements of CO2 and methane
can be used to evaluate the communication paths
between the injectors and producers in combustion
projects.
9. Expected Carbon ∂ Values
o The figure shows the variations in the
methane and Co2, ∂ values encountered
for the combustion process.
o Different fields have different ∂ values
depending on the composition of crude
oil.
o ∂ values for the individual oil fractions
can be heavier in the following order:
saturates, bulk oil, aromatics, resins and
asphaltenes.
10. HEATING PROCESS IN THE
RESERVOIR
Reactions in In-situ combustion occur over a broad
temperature range.
The air/oxygen then passes into the combustion zone,
where it reacts with the deposited fuel to form CO2,
CO, and water.
Ahead of the high temperature combustion region,
thermal cracking produces a fuel, normally called
coke, and volatile gases (such as methane and
ethane).
11. Low-temperature oxidation (LTO)—heterogeneous
gas/liquid reactions producing partially oxygenated
compounds and few carbon oxides
Medium-temperature reactions—cracking and pyrolysis
of hydrocarbons to form fuel
High-temperature oxidation (HTO)—heterogeneous H/C
bond breaking reactions in which the fuel reacts with
oxygen to form water and carbon oxides
In wet combustion- If the water/air ratio is increased to 2.25
to 2.81 kg/std m3 [400 to 500 bbl/MMscf], then the process
is called super-wet combustion.(0.45 to 1.4 kg water/std m3
air[80 to 250 bbl water/MMscf).
Low co2 is produced in the LTO and in Super-wet
combustion zone.
12. Carbon production during In-
Situ combustion
Solution-gas methane of origin should have a ∂ 13C
value near -60°/00.
Methane produced by bitumen pyrolysis should have
a ∂ 13C value between -45 and -50°/00 (extensive
cracking could produce methane with a ∂ 13C value of
about -30 °/00.
CO2 produced from carbonates should have ∂ 13C
values between +25 and -10 °/00.
CO2 produced from combustion of the oil should have
a ∂ 13C value similar to that of the oil, which is near -
30° /00.
13. The non associated (dry) gases -25 to -45 °/00.
Methane originating from bacterial decomposition
range from -60 to-80 °/00
Isotopic composition of thermally generated methane
is a function of the type of source material, the extent
of thermal transformation.
14. Combustion-Tube Data
These runs covered different
formation types (sandstone and
carbonate), different oil types
(heavy oil and bitumen), and
different injection modes (dry,
normal-wet, and super-wet).
The CO2 is analyzed with a stable
isotope mass spectrometer
constructed with Micro mass 903
components for carbon isotope
analysis.
15. Field Analysis and
Interpretation
Normally, the gas, oil, and water properties and rates are
the only data available for interpreting a field project,
without any temperature data.
whether ignition has occurred and the nature of the
reactions occurring at the combustion front.
The early combustion responses are normally interpreted
by gas analyses because these responses are seen within
days or weeks at the production wells.
The normal parameter used to establish whether ignition
has occurred is the absence of oxygen in the produced gas
and an increase in the CO2 conc.
16. Continuation….
The H/C ratio used to indicate the nature of the reactions at
combustion.
For high-temperature combustion, the H/C ratios are
normally in the range of 1 to 2.
As the low-temperature reactions increase , the H/C ratio
also increases.
Oxides/Nitrogen ratio is also used.(Low values low temp.
combustion).
Another method is to use the oxygen/fuel or air/fuel ratio.
CO2 concentration, with a value typically in excess of 13%
showing that high-temperature combustion is occurring
when air is the oxidant.
17. Continuation…..
Using above analyses for interpreting the reactions
occurring in the field is always complicated by
The production of solution-gas methane and CO2 of
carbonate origin, which dilute the combustion-
produced gases and make it difficult.
The possibility of the CO2 dissolving in the oil and
water.
Therefore, carbon isotope analysis used in
conjunction with gas analyses.
It distinguishes the source of the methane and CO2
and the different burning characteristics.
18. CONCLUSION
Carbon isotopic signatures of CO2 will greatly increase
confidence level in reservoir flood predictions and can
be obtained at reasonable expense.
CO2 is highly mobile and detectable at low
concentrations which makes it a powerful predicting
tool in identifying breakthrough, well stimulation
potential and injection profile
More importantly, it provides opportunities for
operational changes that could result in improving the
project economics
19. REFERENCE
K. Rich and K. Muehlenbachs, “Carbon Isotope Characterization
of Migrating Gas in the Heavy Oil Fields of Alberta,
Canada”.1995
Max S. Juprasert, Mark B. Haught, and Martin Schoell, Chevron
Research & Technology Co. "Prediction of Steamflood
Performance Using Carbon Isotope Signatures of
CO2”.1999
Richard Hallam, and R. Gordon Moore etal. “Carbon Isotope
Analysis: A New Tool for Monitoring and Interpreting the
In-Situ Combustion Process”
http://petrowiki.org/In-situ_combustion
Enhanced Oil Recovery Proceedings of the third European
Symposium on Enhanced Oil Recovery, held in Bournemouth, U.K.,
September 21-23,1981
