Article detailing the costs and benefits of applying Enhanced Oil Recovery techniques to ageing and mature fields with examples from India.

1. 64 PESGB May 2016
Enhanced Oil Recovery (EOR) has been implemented
since 1975 to help address growing domestic con-
sumption in India. However, less than 4% of India’s oil
is currently being produced by EOR techniques. Further
resources could be tapped in the future to help reduce
the country’s dependence on imported oil which now ac-
counts for 79% of total consumption. This is particularly
important as India became the 3rd largest oil consumer
in mid-2015, behind China and the United States, with
demand set to rise in line with increases in population
and development.
Two of the basins where EOR has been applied are
the Cambay and Barmer Basins, located in the states
of Gujarat and Rajasthan respectively. The basins
were formed due to continental rifting during the Late
Cretaceous associated with the break-up of the super
continent Gondwana. The rifting created two elongated
NNW-SSE depressions which have been filled with fluvial
and marine deposits resulting in the source, seal and res-
ervoir rocks which are present today. Important trapping
mechanisms include rift related structural traps as well as
stratigraphic pinch outs.
Despite similar evolutions for both basins, there has
been a marked difference in the exploration of the two.
The Cambay Basin has entered into a mature stage after
extensive exploration and production over the past 70
years and still accounts for ~13% of India’s yearly oil pro-
duction. Conversely, the Barmer Basin was unattractive
for exploration until 1999, when new seismic surveying
and processing techniques were applied. A total of 37
discoveries have been made since then and the basin
now accounts for ~23% of India’s yearly oil production.
This paper looks into the impact of two EOR tech-
niques: In-Situ Combustion (ISC) and Chemical Flooding,
in the Cambay and Barmer Basins respectively. The pro-
duction gain from these techniques, combined with cost
reduction through improved efficiencies, could help to
promote the techniques to other fields in the country.
IN-SITU COMBUSTION IN THE CAMBAY BASIN
ISC is a process used in targeting heavy oil reservoirs
(<20.0° API) and can be viewed as having a dual effect
of heating the oil in place reducing its viscosity as well as
gas injection increasing reservoir pressure. Oil is ignited
in the reservoir by the injection of hot air and/or lowering
heaters down injection wells forming a fire front (Figure-1).
With continued injection of air, combustion is maintained
at around 350-450°C utilising only a small percentage
of oil in place as fuel. As the fire front sweeps through
the reservoir, the remaining oil ahead of the fire front in-
creases in temperature and reduces in viscosity, mobilis-
ing it towards producer wells. The combustion effect also
generates flue gasses which have the additional effect of
charging the reservoir with a secondary gas cap, increas-
ing the reservoir pressure, resulting in additional mobi-
lisation of oil. As with other gas injection schemes, ISC
also requires the process to begin up-structure, forcing
oil down dip through gravity drainage towards producer
wells. Combinations of pattern or line drive well configu-
rations have been applied in the past.
Balol and Santhal fields, operated by Oil and Natural
Gas Corporation Ltd. (ONGC), are located in the north
of the Cambay Basin and are the sites of two out of only
four commercial ISC EOR schemes currently operational
worldwide. The fields are part of a NNW-SSE striking
narrow heavy oil belt within the Eocene Kalol Formation,
which is host to thick fluvial channel sandstone bodies
with good quality reservoir characteristics. The Kalol
Formation can be subdivided into the KS-I, II and III pay
zones with the KS-I being the most important contain-
ing ~80% of OIIP. At both fields, the KS-I pay zone has
a porosity of ~28%, permeability between 3,000-8,000
mD and a thickness ranging from 2-10 m. The oil water
contact ranges between 988-1,018 m with the oil having
an API gravity of 13-18° and a viscosity of 150-1,500 cp
making it very immobile within the reservoir.
Santhal, containing 351 MMbo OIIP, is located in the
southern end of the heavy oil belt and is separated by an
E-W fault to Balol, lying immediately to the north, con-
taining 168 MMbo. Balol was discovered in 1970 a year
before Santhal and they were both put on conventional
production in a 300 m x 300 m well pattern configuration
in 1985 and 1974 respectively. There is a strong active
edge water drive present at both fields and due to an ad-
verse mobility contrast between the heavy oil and water,
primary recovery was fairly low: <13% at Balol and <17%
at Santhal. Peak oil production at Balol was achieved in
1991 with a rate of ~6,600 bo/d, but had declined to
News Feature
Tristan Reilly – Field Researcher, IHS
Advantages of Enhanced Oil Recovery
Techniques in the Cambay and Barmer
Basins, Western India

2. PESGB May 2016 65
~2,500 bo/d with 75% water-cut in early 1997. Santhal
also experienced declines in production from a peak of
~11,500 bo/d in 1987 declining to ~4,700 bo/d also with
a water-cut of 75% in early 1997.
It became apparent that thermal stimulation of the
oil was required to target the heavier oil accumulations
within the reservoir. Cyclic Steam Injection and ISC were
both considered but ISC was adopted as the thin res-
ervoir with its moderate depth meant that steam injec-
tion would condense too quickly downhole for it to be
effective. Accordingly, in 1990 ONGC conducted a pilot
ISC scheme in a pattern configuration at the Balol field
which yielded encouraging results. The similar charac-
teristics of the Santhal field meant that full implementa-
tion of ISC techniques were applied there in April 1997
without a pilot study, followed by full implementation at
Balol in October 1997. Air was injected at pressures of
1,200-1,600 psi with peak injection rates of 17.6 MMcf/d
at Balol and 53.0 MMcf/d at Santhal both achieved in
mid-2004.
Initially, pre-existing infrastructure was utilised whereby
former producer wells were converted into air injection
wells. However, it soon became apparent that re-com-
pletion and the drilling of purpose designed injection
wells was required with optimal cement and metallurgy
for ISC as the original wellbores became heavily cor-
roded. Additionally, newly designed air injectors were
required as a number of complications and explosions in
the early stage injectors hampered production. Important
safety considerations were also developed to deal with
produced flue gasses including H2S, CO2 and SO2
which necessitated careful handling at the surface.
The implementation of ISC technology resulted in a
reduction in water-cut and an increased production
rate (Figure-2). Critically, an increase in the recoverable
volume at Balol to 65 MMbo (39% recovery) and 153
MMbo (43% recovery) at Santhal was achieved.
Figure 1: Schematic diagram indicating the temperature pro-
file in the reservoir during ISC
Figure 2: Graph indicating the arrest in production decline due to the implementation of ISC

3. 66 PESGB May 2016
CHEMICAL FLOODING IN THE BARMER BASIN
Chemical flooding techniques have been developed since
the late 1960s to alter the physicochemical properties of
the injected fluid and those of the oil in place, to aid in
the mobilisation of oil which would be by-passed during
normal waterflood operations. Adding high molecular
weight polyacrylamide and other long chained polymers
to the injected fluid increases the viscosity to that of the
oil in place. This reduces the mobility contrast between
the two fluids and increases the sweep efficiency as a
more uniform displacement front is formed throughout
the reservoir, combatting the effects of reservoir hetero-
geneities which can cause water-fingering (Figure-3). The
addition of alkali and surfactant chemicals to the polymer
flood (ASP Flood) can help to emulsify residual oil, lower-
ing the interfacial tension between the oil and water and
in doing so, promote oil mobility within the reservoir.
Polymer and ASP schemes are being implemented in
the Lower Paleogene Fategarh Formation in the Mangala,
Bhagyam and Aishwariya (MBA) fields in the Barmer
Basin, operated by Cairn India Ltd. (CIL). All three fields
were discovered in 2004; Mangala, the largest, holds
1,283 MMbo OIIP followed by Bhagyam and Aishwariya
at 557 MMbo and 540 MMbo respectively. The Fategarh
Formation consists of fluvial sandstones, siltstones and
conglomerates. The reservoir is thicker and of more op-
timal reservoir quality in the north of the basin in the area
of the MBA fields, with porosities between 21-30% and a
permeability of ~5,000 mD. The reservoir is also relatively
shallow at ~700 m and as such the reservoir pressure is
moderate-low at 1,625 psi. Additionally, the oil in place
has a high paraffin wax content (~25%), moderate vis-
cosity (10-20 cp) and medium gravity (~27° API), making
it fairly immobile within the reservoir.
Mangala was placed on water injection from the begin-
ning of production in 2009 with an expected recovery of
35%. The IOR operation saw a large rise in water cut as
water fingering was exacerbated thus requiring a large
amount of water treatment. To combat water fingering
and high water cut, a pilot EOR scheme was implemented
in Q4 2010 in which 4 injector wells were drilled in a 100
m x 100 m square with a producer well at the centre.
By August 2011 the pilot polymer injection phase was
initiated; water-cut declined to ~30% for 4-5 months and
resulted in an 11% increase in production rate over wa-
terflood. By October 2012, ASP injection began and dem-
onstrated the mobilisation of un-swept oil post polymer
flooding, resulting in a decrease in water cut by 20-30%
lasting for 2.5 months after initial injection. Lab testing in-
dicated that 10-15% incremental recovery would also be
achieved over polymer flooding. Further polymer injection
and final water injection stages were then conducted.
In October 2014 CIL began full field implementation of
polymer flooding at Mangala and by the end of 2015 pro-
duction reached 19,000 boe/d. By January 2016 ~330,000
bbl/d of polymer was being injected and this is scheduled
to increase to a maximum injection rate of 400,000 bbl/d
in Q4 FY17. When full implementation is achieved across
all the MBA fields, CIL anticipates producing >300 MMbo
incremental over 636 MMbo expected from water flooding
alone which is reported, by the company, to be the world’s
largest chemical flood operation.
IS EOR THE KEY TO A BRIGHTER PRODUCTION
FUTURE IN INDIA?
The application of EOR to existing fields could be a more
attractive proposition to operators as a means of achiev-
ing more rapid increases in production, compared with
the longer turn-around time of new exploration and de-
velopment projects. Cost is still the main issue for EOR
application, but this could be improved with greater ef-
ficiencies and technical capabilities. Both ONGC and CIL
have demonstrated this in becoming world experts with
respect to some of the technological innovations applied
in the Cambay and Barmer Basins.
ISC has been proven to be effective in producing heavy
oil and IHS has estimated the operational costs to be ~$16/
bbl and ~$20/bbl at Balol and Santhal respectively. This
moderate cost level means that the process is an economi-
cally viable technique even in the current low oil price envi-
ronment (<$40/bbl). ONGC has now begun implementing
the ISC technique at the Lanwa field lying to the immediate
north of Balol. Initially, Lanwa was developed for primary
production in 1986 on the same well pattern configuration
as Santhal and Balol. In 1992 an ISC pilot study was un-
dertaken at Lanwa but full field implementation was not ap-
plied due to the presence of problematic coal layers caus-
ing safety and operational concerns. However, geocellular
modelling in 2004 highlighted safer areas for ISC operation,
leading to the field being included in ONGCs redevelop-
ment plans for the area in 2012 for full ISC implementation.
Chemical flooding, meanwhile, can be applied to a large
range of field types and it is this versatility, coupled with
further cost reduction, which makes the technique increas-
ingly more attractive. IHS estimates the polymer injection
process at Mangala to cost ~$11/bbl extracted and CIL
aims to see production costs reduce to <$10/bbl after
full implementation is achieved in FY17. With the cost ef-
ficiencies in mind, the technique has also been applied by
ONGC at the Bechraji field, lying <10 km to the west of
Santhal. Bechraji originally underwent an unsuccessful ISC
pilot in 2002 but a chemical flood EOR pilot scheme was
conducted there in FY15. The chemical flood operation
showed positive results and it is now believed that a full
implementation development plan is under consideration.
For further information please contact:
Anthony Jaep,
Field Researcher – NW Europe, IHS
Anthony.Jaep@ihs.com
News Feature
Advantages of Enhanced Oil Recovery
Techniques in the Cambay and
Barmer Basins, Western India (cont.)