GAS HYDRATE STUDIES IN ONGC APPROACH

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Feb 22, 2014 (3 years and 3 months ago)

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GAS HYDRATE STUDIES IN


ONGC APPROACH


B.K.VARMA,

KDMIPE, Oil and Natural Gas Commission, DehraDun



ABSTRACT
:

Gas hydrate is one of the non
-
conventional source of energy identified recently by ONGC worthy to be studied
for possible exploration and explo
ration to meet the burgeoning demand of hydrocarbons and ensuring energy
security for the country, ONGC has set three milestones viz., (1) Estimation of gas hydrate and free gas
underlying gas hydrate resources in the Indian deep offshore from seismic data

and geological information, (2)
Sampling hydrated sediments in identified areas (3) Development of technology for their exploitation in
collaboration with universities and organizations from India/abroad to meet the above objectives in the interest
of the

country. As a first step, studies of existing seismic data was initiated in 1996. Preliminary analysis of
seismic data along the east and West Coast deep
-
water area of India has brought out about 80,000 sq.km. area
having potential hydrate deposits in An
daman
-
Nicobar, Krishna
-
Godavari, Konkan and Kutch offshore. With
advancement in geological and geophysical understanding ONGC confirmed about 1400 sq.km. area in
Krishna
-
Godavari deep offshore as potential hydrate province based on seismic attributes viz.
interval velocity,
polarity, amplitude vanstion with offset at bottom simulating reflector (BSR) level and other geoscientific
information (bathymetry structure, thickness of hydrate stability zone (HSZ), rate of sedimentation, depositional
set up, TOC et
c.)



Thus, technological milestone to evaluate hydrate potential from seismic data is partly achieved through
R&D efforts. Further, sampling at identified locations will help in understanding the processes of hydrate
formation and its habitats and in cal
ibration of the seismic data leading to refined resource/ reserve estimate.
These parameters are critical for effective planning of exploration. The other areas are under study for
assigning priorities based on the hydrate potential so that a comprehensi
ve techno
-
economic perspective can be
evolved to initialise hydrate exploration operation in Indian environment prior to their cost
-
effective
exploration.


INTRODUCTION:

Naturally occurring gas hydrates are ice like compounds in which gas molecules, methan
e in
most cases, are en
-
eaged in interstices for hydrogen bonded water lattices at low temperature and
high pressure. The first evidence of such naturally occurring gas hydrate deposits was found in
Messiyokha field in Russian permafrost region. Subsequen
tly gas hydrates were also found in
shallow marine sediments of arctic region during various ODP legs in tropical deep
-
water areas
where water depth exceeds 650
-
750 meters, the pressure temperature conditions are favourable for
formation of gas hydrates.
Gas hydrates accumulation in deep
-
water areas is believed to be due to
accumulation of biogenic methane generated in shallow sediments. Area with higher sedimentation
rates are thus favourable for such accumulation as the organic carbon is preserved due
to its rapid
burial.



The fact that 164 cubic meters of methane gas is trapped in one cubic meter of gas hydrate
and large area of deep water have favourable conditions of formation for gas hydrate makes it a
suitable candidate as an alternative sourse o
f energy. In view of this goal, in 1997 a National Gas
Hydrate Programme was launched by MOPNG. Simultaneously ONGC, GAIL and DGH started in
house studies for evaluation of gas hydrates in Indian offshore areas.


In India ONGC is the only agency equipped

with the capability for evaluation of gas hydrate
potential due to its inherent strength in terms of expertise on acquisition, processing and
interpretation of seismic data. Reallsing its national obligation and possibility of exploitation of gas
hydrat
es as a future business opportunity. ONGC has taken up the job of detailed
planning/implementation of various aspects of gas hydrate exploration and exploitation. The first step
towards such studies was initiated in 1996. Preliminary analysis of seismic

data along the Eastern
and Western deep water area of has India brought out the potential areas for gas hydrate occurrence
which includes the area of Andaman
-
Nicobar, Krishna
-
Godavari, Konkan and Kutch offshore upto a
bathymetry of 3000 meters.


INITIAL S
TUDIES:

Major part of the deep water areas of India is covered by Multi channel Seismic data acquired
by ONGC. Although way back in 1984, BSR was identified and reported in Andaman area (Chopra
N.N., 1984), in integrated study for identification of gas hy
drate prone areas of Indian offshore was
taken up only in the year 1996. During this study the existing data beyond 600m. Isobath was
scanned for evidences of gas hydrate based on the attributes of BSR like Blanking, Polanty Reversal
etc. A qualitative m
ap prepared based on this study has brought out about 80,000 sq. km of area in
the Indian deep waters upto 3000 meters isobath, as favourable for gas hydrate occurrence (Kuldip
Chandra etal., 1998). Reprocessing of seismic data was suggested for confirmat
ion of BSR in the
favourable areas. Work Association with Dr. T.Yuan, from Uvie, Canada was conducted during May
1997 to October 1997, through which a methodology was developed for reprocessing of seismic data
for gas hydrate. This methodology stressed t
he importance of velocity analysis in the hydrate stability
zons (HSZ). Fourteen seismic lines segments distributed in East and West Coast deep water were
reprocessed during this work association. Very clear BSRs cutting across sedimentary sequences
supp
orted by interval velocity inversion were observed beyond 800
-
900 m bathymetry in few lines of
Krishna Godavari deep offshore. This study had brought out that Easter offshore is more favourable
as compared to western offshore.


IN
-
HOUSE STUDIES:

Bathymetr
y maps for Eastern and Western offshore areas of India were prepared which helped
in understanding seafloor morphology. Based on the encouraging results of initial studies, Krishna
-
Godavari offshore area was taken up for detailed study. Twelve Seismic lin
es were reprocessed in
this area and 1400 sq.km area was identified as gas hydrate prone. Taking in to consideration the
hydrated sediment velocity of 1700
-
1900 and non
-
hydrated sediment velocity of 1500
-
1600 as
observed from stacking interval velocity, g
eological consideration of high sedimentation rate and rich
organic content an estimate of gas resources of this area was made which works out to be about 350
-
900 bcm. As this is a very crude estimate due to the limitations in picking stacking velocity, f
urther
efforts are to be made for the accurate assessment of the saturation of gas hydrates and underlying
free gas using refined methods. To know the ground truth and for callbration of results obtained from
seismic, sampling of the identified BSR zone by

drilling is essential Plans to collect sea bottom
samples for Geo
-
chemical studies are in the pipeline. Parallel initiatives for R&D work in Drilling,
Production and transporation are to be taken up.


ONGC’s VISION:

The approach adopted by ONGC is to uti
lize the existing data and to develop in house or
obtain capability to reach the goal of exploitation of gas hydrates. Exploitation from relatively softer
targets of underlying free gas is to be taken up first. Studies in logistically best suited and mor
e
favourable Geological setting conducive to gas hydrate formation and areas of high density of gas
hydrate occurrence are to be taken up in the initial phases. Efforts for estimating the resources of
hydrates for deep offshore areas are to be continued.

Research & Development efforts are to be
continued to help materialize commercial exploitation of this non
-
conventional hydrocarbon of vast
resources within a few next decades.


RERERENCES:

1.

Andressen, K.Kart P.E. & Grantz . 1995, “Seismic Studies of Botto
m

simulating reflaction
related

to gas hydrate beneath the continental margin of beau fort sea”, JGR,
vol. 100, B7, 12859
-
673.


2.

Chopra, N.N. 1985 “Gas hydrate An unconventional Trap in Fore Act regions of the Andaman
offshore” Bulletin of ONGC, Vol.22 J
une 1985.

3.

Dillan, W.P. & Pauli, C.K. 1983 Marine gas hydrates the Geophystcal evidence” Natural Gas
Hydrate”, properties, accurrences and Recovery, J.L. Cox Ed. 7390 Butter worth publishers, Boston
Mass

4.

Hyndman, R.D. & G.D. Spence 1992 “A seismic study of
methane hydrate marine bottom
simulating reflector” J. Goophysics Res. 97,6683 6608.

5.

Kuldeep Chandra Singh RP & Julka A.C. 1998 “Gas Hydrate Potential of Indian Offshore Area” ,
2
nd

Conference and Exposition on Petroleum Geophyssics SPG 98 Chennai (INDIA
)

6.

Yuan, T. 1997, “Evaluation of Seismic data to determine gas hydrate potential of deep offshore
regions of India”, Unpublished report of ONGC.