National Geophysical Research Institute, Hyderabad
Outline of the lecture
Need for EOR
CO2 sequestration
Possible potential CO2 traps
4D Monitoring and EOR
Conclusions
Need for EOR
In India only about 27% of the oil in-place is
being produced economically. Recovering these
remaining oil and gas resources poses
formidable technical and financial challenges.
To wring even the last drop of oil economically
from reservoir, lot of research work is going on
for enhanced oil recovery (EOR) so that
premature abandonment of wells can be
checked.
CO2 sequestration
Geological sequestration of carbon
dioxide is a means of its injection in a
suitable geological formation.
Typically below 1 km depth where
temperature and pressure are above the
critical point for carbon dioxide (31.60C,
7.38MPa).
Geological CO2 sequestration
Characteristics of favourable traps
for CO2 sequestration
Geological reservoirs for safe and long
storage for carbon dioxide must meet
certain criteria. Some favourable
geological traps based on reservoir
characteristics
such
as
porosity,
permeability, and their affinity for the
chemical reactions are discussed below:
1. Perfect sealing so as to preserve it for
long geological time, leakage could lead
to environmental disaster
2. Suitable porosity, permeability and
presence of suitable reactants like brine,
are some of the criteria of good
sequestration sites.
Possible potential CO2 traps
There could be several possible traps for
efficient CO2 storage, few known traps are
discussed here:
1. Abandoned hydrocarbon reservoirs
2. Mature (Brown) oil fields
3. Non-economic coal seams
4. Shale formations
5. Basalt formations
1. Abandoned hydrocarbon reservoirs
1. These are the geological settings in which
oil/gas was trapped for long geological
time.
2. These abandoned reservoirs are the best
possible locales vacated by the natural oil
and gas where carbon dioxide can be
stored.
3. These reservoirs have proven capacity of
holding natural oil and gas and have good
sealing.
4. Under high pressure carbon dioxide turns
into liquid (super critical carbon dioxide)
and when injected in the reservoir it is
trapped below an aquiclude or seal (cap
rock).
2. Brown Oil Field: Enhanced Oil
Recovery
In a brown field sequestering carbon dioxide
becomes an additional advantage because it
helps in enhanced oil/gas recovery.
The injected carbon dioxide dissolves in the
oil and reduces its viscosity. This is indeed
one of the best known commercially viable
methods to enhance the secondary recovery
from the oil fields.
Carbon dioxide injection for
Enhanced Oil Recovery
4D Monitoring
Monitoring of sequestered carbon dioxide is
key concern to assure the inhabitants and to
policy makers that it has no disastrous /
adverse effect on the environment. Monitoring
will also demonstrate success/failure of
sequestration.
Sequestration can be better planned by
monitoring the carbon dioxide storage by
finding those pockets of the reservoir which
are yet to be flooded with the carbon dioxide.
Indian Case study: Monitoring of
thermal front in Balol oil field
There is no case study available for any Indian
oil field with CO2 injection; however, thermal
recovery technique (in-situ combustion)
similar to CO2 injection, has been successfully
attempted.
A pilot study to monitor the thermal front
caused by insitu-combustion in Balol heavy
oil field, Cambay basin, was conducted.
Time lapse (4D)seismic data was used for
monitoring of the thermal front movement.
Three sets of 3D seismic data acquired in 1
year interval were analyzed.
Case Study
Balol oil field lies
in the heavy oil
belt in the northwestern part of
the Cambay Basin,
India
The reservoir zone is 32 m in thickness and top
of the reservoir is at depth of 996 m and bottom
of the reservoir lies at 1029 m depth. The
porosity of reservoir is in the range of 28-30%
and its permeability varies from 8-15 darcy.
o
At reservoir temperature of 72 C and pressure
of 104 kg/cm2, the viscosity of oil varies from
o
100-450 Centipose and its gravity is about 15.5
API (Heavy Oil).
The primary recovery of viscous and heavy oil
from Balol is only 10-12%, hence the pay zone is
under thermal EOR process (Insitu Combustion).
Insitu Combustion Process
Producer
Injector
air/water
Burning
Front
Oil
Bank
light oil
B
M1
M2
Full stack section of migrated data along inline 633 for
base (top), monitor 1 (middle) and monitor 2 (bottom).
B
Base – Monitor1
(Before 4D analysis)
M1
Diff
B
Base – Monitor1
(After4D analysis)
M1
Diff
B
Base – Monitor2
(Before 4D analysis)
M2
Diff
B
Base – Monitor2
(After4D analysis)
M2
Diff
Thermal front movement near injectors (approx. 50m / year
radially). Yellowish colour near injectors shows anomalous
regions, which represents thermal front movement.
Inversion results
Constant time slices of
inverted P-impedance are
in a 10 ms window
centered at 900ms for
baseline, monitor1 and
monitor2 surveys.
We see a drop in impedance from
baseline to first monitor survey near all the
injectors. Low impedance anomalies near
the injector wells 145, 147, 153 and 162
are identifiable in these figures and are
indicative of the effect of combustion.
Conclusions
Carbon dioxide injection serves two
purposes, one to reduce CO2 from
atmosphere and other to enhance oil
recovery from brown oil fields.
Geological sequestration of carbon dioxide
to reduce global warming is an active area
of research.
NGRI has taken a lead role to launch a
project on Deccan Volcanic Province with
financial support of DST, Govt. of India, as
a pilot project.