Article detailing the potential of methane hydrates and their future effects on the Indian gas industry

1. 40 PESGB March 2017
Tristan Reilly
Senior Technical Researcher, E&P Fields – IHS Markit Ltd
Deep Marine Gas Hydrates
An Answer to India’s Growing
Energy Requirements?
PES
MARINE GAS HYDRATE FORMATION
Gas hydrate is a crystalline solid which is the product of natu-
ral gases, such as methane, coming into contact with water in
low temperature (4 – 10 °C) and high pressure (10 - 30 MPa)
conditions. These are the prevailing conditions in the upper stra-
tigraphy of deepwater sediments (>400 m water depth) where
un-trapped gaseous hydrocarbons react with in-situ connate
water. The reaction causes gas hydrates to crystallise within the
pore spaces of the sediments in clathrate compounds whereby
water forms a lattice or cage surrounding gas molecules creat-
ing a substance similar in texture and appearance to ice. Vast
amounts of hydrocarbons can be trapped in this manner with
every m3 of solid gas hydrate containing up to 164 m3 of gase-
ous methane.
Gas hydrates form within unlithified deep sea sediments in a
stability zone which is defined by the temperature with respect
to depth below the ocean floor. Temperature within the sedi-
mentary layers generally increases with depth in a relatively con-
stant manner meaning that at a certain depth below the ocean
floor (usually 150 - 400 m depth) gas hydrate will not form and
will remain in a gas saturated water solution. Above this critical
depth, gas hydrate is stable and forms a zone of relatively uni-
form thickness following the bathymetry of the ocean floor and
not necessarily conforming to the orientation of sedimentary
layers and structures. The hydrate also forms a seal to any free-
gas beneath the stability zone as it fills the porosity of the sedi-
ment blocking upward gas migration. The bottom of the stability
zone can be identified in seismic surveys as a high-amplitude
Bottom Simulating Reflector (BSR) which mimics the topology
of the ocean floor reflector but has the opposite polarity and can
cut across dipping strata.
INDIAN EXPLORATION EFFORTS
In 1997, the Indian Ministry of Petroleum & Natural Gas
(MoPNG) set up the National Gas Hydrate Program (NGHP)
to work closely with the Directorate General of Hydrocarbons
(DGH), national research institutions (NIO, NGRI and NIOT) and
national E&P companies (ONGC, OIL, GAIL and IOC) with the
India is expected to become the world’s
third largest energy consumer by 2020 due
to its expanding economy and population.
Energy security is vital for India’s ambitions
for continued development but the country
is becoming increasingly dependent on
foreign gas imports to meet the country’s gas
demand. Imported LNG has risen from 22.7%
of gas consumption in 2009-10 to 45.5% in
2014-15 and is expected to increase further
(IHS Markit Ltd., 2016).
In recent years there has been a greater
impetus on domestic conventional gas
resource identification and extraction with the
government attempting to reduce the amount
of regulations on the petroleum industry and
boost investment. Longer term, one area
which has been identified as a potential way
of increasing production is by unlocking gas
hydrates from under the ocean floor. India
is estimated to have as much as 66,900 Tcfg
located in India’s deep water regions (AK
Jha, SPE, 2012). This volume is 420 times
the estimated 157 Tcfg of India’s in place
conventional gas (IHS Markit, 2016). Despite
these extraordinary volumes and with gas
hydrates being a relatively clean fossil fuel, the
technology to produce gas hydrate remains
at the theoretical and testing stages. This
article will look at gas hydrates located in deep
marine conditions; how they are formed, how
they are imaged and how they could potentially
be extracted. The other main type of location
in which gas hydrate is found is in extremely
low temperature conditions, predominantly
inside the permafrost of the Arctic Circle, and
is outside the scope of this article.

2. PESGB March 2017 41
desired aim of understanding gas hydrate exploration
techniques and possible methods of safe and cost ef-
fective extraction. Seismic surveys off the East and West
Coasts of India and the waters around the Andaman
Islands, during the late 1990s and early 2000s, indicated
large expanses of gas hydrates in the Krishna-Godavari,
Andaman, Mahanadi and Kerala-Konkan Basins with sig-
nificant deposits in other areas (Figure 1).
The NGHP, in partnership with the USGS, undertook an
exploration program, NGHP-01, between April - August
2006, at a cost of USD 36 million, focusing on the four
main prospective basins which had been previously
identified in seismic studies. A total of 21 drill sites were
established; 1 site in the Kerela-Konkan, 15 sites in the
Krishna Godavari, 4 sites in the Mahanadi and 1 site in
the Andaman. Utilising the drillship ‘Joides Resolution’,
a total of 39 wells were drilled, 27 with cored holes, 13
with wireline logged holes and 12 with LWD-MWD holes
and a total of 6 VSP surveys shot. More than 9,250 m
of sedimentary records were taken with 2,850 m of core
recovered. Gas hydrate was found to be predominantly
located in coarse grained (mostly sand rich) sediments as
well as sub-vertical fracture sets (mostly in low porosity
clays/shales). The calculated depth based on the BSRs
imaged in seismic studies also correlated well with the
base of the gas hydrate stability zone (BGHSZ) derived
from recorded temperature profiles within the wells. The
highlight of the expedition included the identification of
one of the world’s richest gas hydrate deposits at well-
site NGHP-01-10 in the Krishna Godavari Basin where
deposits were found in the fracture sets of a shale domi-
nated area. Furthermore, one of the world’s deepest and
thickest occurring deposits worldwide was discovered at
wellsite NGHP-01-17 in the Andaman Basin where gas
hydrate was recorded at depths over 600 m below the
ocean floor.
N E W S F E AT U R E
Figure 1 - Map detailing gas hydrate thickness concentrations in the Indian Ocean.
Adapted from DGH Presentation, 2011

3. 42 PESGB March 2017
PES
At the beginning of March 2015, the NGHP con-
ducted another expedition, NGHP-02, which was
undertaken off the east coast, also in conjunc-
tion with the USGS, at a cost of USD 92 million.
The expedition’s aim was the targeting of deeper
water, toe-of-slope, coarse, sand rich dominated
strata that were deemed most suitable for future
gas production. A total of 25 drill sites were select-
ed in the Krishna-Godavari and Mahanadi Basins
based on data recorded during the NGHP-01 ex-
pedition and additional seismic surveys. The sites
were the locale for 42 exploratory holes drilled
from the drillship, ‘Chikyu’, in water depths ranging
between 1,519 – 2,815 m, with subsea comple-
tion depths ranging between 239 – 567 m. A total
of 6,659 m of sedimentary section was logged by
LWD and wireline methods, in 25 and 10 of the
holes respectively. A total of 2,271 m of core was
also recovered from 16 of the holes with the for-
mation temperature measured ahead of the drill
bit. Significantly, 156 m of pressurised core was
recovered, preserving the in-situ conditions of the
gas hydrate for either mechanical triaxial testing or
to be quantitatively degassed for hydrate concen-
tration analysis. A Modular Dynamic Tester (MDT)
was also employed; successfully flow testing gas
in 2 holes. The expedition confirmed the presence
of large, highly saturated gas hydrate deposits
within the coarse grained sand-rich sediments as
expected, helping to validate the NGHP’s depo-
sitional models. Effective permeabilities were also
shown to be significantly higher than previously
interpreted laboratory and field studies.
It became apparent that reservoirs within the
Mahanadi Basin were limited by the availability of
gas to charge the depositional systems. However,
Krishna Godavari deposits showed a high degree
of charging, especially within two study areas. The
study area drilled by the wells NGHP-02-16, 17,
20 & 21 targeted a regional anticline with a well-
defined BSR (Figure 2). The prospect contained
two significant reservoirs with high levels of gas
hydrate saturation through a combination of frac-
ture filling and pore filling gas hydrates.
An even more significant accumulation was en-
countered by the wells NGHP-02-08 & 09 which
intersected a large channel levee complex with
a reasonably well developed BSR (Figure 3). The
wells had discovered a fully developed gas hydrate
depositional system after encountering a 50 m
Deep Marine Gas Hydrates
An Answer to India’s Growing Energy Requirements? (cont.)
Figure 2 - Krishna Godavari Basin seismic section through
regional anticlinal prospect drilled by the NGHP-16, 17, 20 & 21
wells. NGHP-02 Expedition, 2015
Figure 3 - Krishna Godavari Basin seismic section through
channel levee complex drilled by the NGHP-08 & 09 wells. NGHP-
02 Expedition, 2015

4. PESGB March 2017 43
For further information please contact:
Anthony Jaep,
Field Researcher – Europe, IHS Markit
Anthony.Jaep@IHSMarkit.com
N E W S F E AT U R E
section which showed very high gas
hydrate saturation and high porosity.
ONGC sources estimated the find to
be as large as 134 Tcfg GIIP.
POTENTIAL EXTRACTION
TECHNIQUES
The solid state of gas hydrate makes
it very difficult to extract from be-
neath the ocean floor compared to
fluid gas extraction from convention-
al reservoirs. A number of ways to
initiate the production process have
been theorised including depressuri-
sation, thermal stimulation, inhibitor
injection and CO2/N2 replacement.
1) Depressurisation involves pro-
ducing any free gas from beneath
the gas hydrate stability zone, reduc-
ing the pressure below the pressure
stability limit of the hydrate, thus lib-
erating gas.
2) Thermal stimulation is a pro-
cess whereby the reservoir is heated
by processes including hot water/
steam injection, internal combustion
or applying a voltage. The extra heat
within the reservoir would ‘thaw’ the
hydrate, releasing gas.
3) Inhibitor injection involves the
injection of chemicals such as meth-
anol and glycol into the reservoir
which shifts the chemical equilibrium
of the system, reducing the freezing
point of the hydrate, making it desta-
bilise and liberate gas.
4) CO2/N2 replacement is a pro-
cess whereby CO2 and N2 are
injected into the reservoir and the
molecules preferentially replace
the hydrocarbon molecules locked
within the water lattice structure. This
carbon sequestration process also
has major incentives as an environ-
mentally friendly technique.
There has been no commercial
production of gas hydrates to date
but the largest step towards pro-
duction was taken in March 2013
by a Japanese collaboration. The
Japanese Ministry of Economy,
Trade and Industry (METI) and the
Japan Oil, Gas and Metals National
Corporation (JOGMEC), amongst
others, undertook a test produc-
tion study at the AT1-P wellsite at
the Daini-Atsumi Knoll in the east-
ern Nankai Trough, Pacific Ocean.
Gas was produced at ~700,000
cfg/d for 6 days before major sand
ingress halted the operation. The
process followed the ‘depressurisa-
tion’ model and demonstrated the
production potential from marine gas
hydrates even though only a small
amount was produced.
Gas hydrate extraction requires
major environmental and safety
considerations. During production,
the unlithified sedimentary pile may
destabilise as the solid hydrate be-
comes liquid and gaseous. This is of
particular concern as the wellbore in-
tegrity may be compromised as well
as causing ocean floor slumping and
subsidence. Additionally, methane is
a much more potent greenhouse gas
than CO2 and if the gas liberation
process becomes uncontrolled, any
escaped gas may further compound
the greenhouse effect. The pump-
ing of methanol, glycol, CO2 and N2
into the ocean floor also poses major
technical challenges requiring mitiga-
tion against leakage into the ocean
ecosystem. It is widely understood
that a combination of the different
extraction techniques would be op-
timal to minimise ocean floor insta-
bility and to mitigate environmental
damage.
THE FUTURE OF GAS
HYDRATE
Gas hydrate is one of the largest
sources of hydrocarbons on earth
and has the potential to become
an important clean energy alterna-
tive of the future. It is expected that
gas hydrates will have a large effect
on the world gas market when it is
harnessed, especially if countries
like India and Japan, which import
large amounts of LNG, can develop
domestic gas hydrate industries of
their own. However, the technology
for gas hydrate extraction is still in its
infancy and there are many challeng-
es still to overcome. In 2014, the Oil
and Gas Financial Journal estimated
the current cost to produce gas hy-
drates was USD 30 – 50 /MMBtu
which is much higher than current
LNG landed price of around USD 3 –
6 /MMBtu. The International Energy
Agency has estimated that it will be
2030 before gas hydrate becomes
commercially viable, with the cost
projected to have reduced to USD
4.70 – 8.60 /MMBtu.
The NGHP has provided an excel-
lent opportunity for industry, aca-
demia and government to increase
the understanding of marine gas hy-
drates in India. The two expeditions
carried out over the last decade,
coupled with laboratory research
and seismic surveying have been
instrumental in creating advanced
depositional models and the devel-
opment of innovative exploration
techniques. The expeditions also
provided an unprecedented amount
of core, wireline and sample data
which will prove invaluable in the
organisation’s ongoing research. In
2017, the NGHP intend to under-
take production testing at the chan-
nel levee complex discovered by
the NGHP-02-08 & 09 wells in the
Krishna Godavari Basin. The tests
aim to build upon the success of
the 2013 Japanese test production
study and will undoubtedly lead to a
more comprehensive understanding
of gas hydrate extraction marking
the next major milestone in the story
of gas hydrates.