The Andaman-Nicobar basins were formed by the convergence of the Indian and Burmese tectonic plates. Exploration has found evidence of oil and gas deposits within the basin. Fifteen exploratory wells have been drilled, with one discovering gas from Middle Miocene limestone. The basin shows potential for hydrocarbon reserves based on its geological history and similarities to productive neighboring basins, but commercial production has not been achieved. Further exploration is needed to appraise the full oil and gas potential of the Andaman-Nicobar basins.

1. ANDAMAN-NICOBAR
BASINS
BY
SYED NAWAZ
M-TECH 1ST SEM
PETROLEUM EXPLORATION AND PRODUCTION
DELTA STUDIES INSTITUTE, ANDHRA UNIVERSITY

2. Content
• Basin introduction
• Tectonic history
• Generalized stratigraphy
• Stratigraphy traps
• Exploration status
• Hydrocarbon potential

4. Basin introduction
• Basin location : SE part in Bay of Bengal
• Lies in category II Sedimentary Basin (Known accumulation of HC but
no Commercial Production)
• Area 47,000 Sq.km
• This basin forms by a typical Island arc system from Myanmar (N) –
Indonesia (S).
• Basin is a result of the northward movement of the Island Plate and
its under thrusting under the Asian plate in the Cretaceous time.

5. Arc System
• Oceanic plate subduct another oceanic plate and results in melting
the magma and that magma rise to surface and a series of volcanic
island is going to popup in the ocean parallel to trench
• Subduction is a geological process that takes place at convergent
boundaries of tectonic plate where one plate moves under another
and is forced to sink due to gravity into the mantle

6. • Evolved due to a convergent plate movement between Indian plate and
west Burmese plate
• Subduction progressed, the Outer High Arc complex started rising steeply,
thereby creating a Fore Arc basin between Volcanic Arc and the Outer High
Arc.
• Continued thrusting caused uplift and formation of the Andaman Nicobar
Ridge as a chain of Islands.

7. Evolution of Andaman
Basin:Schematic
Representation.

8. Tectonic history
• It has evolved through convergent plate boundaries between Indian
plate and west Burmese plate.
• Major Tectonic elements of Andaman-Nicobar region are:
• Outer High/Trench slope break
• Fore Arc Basin
• Volcanic Arc
• Back Arc Basin
• Mergui Terrace

10. • A forearc is the region between an oceanic trench and the associated
volcanic arc, Back-arc forms behind an island arc.
• A volcanic arc is a chain of volcanoes formed above a subducting
plate,

12. Generalized stratigraphy
• Habitat Of Oil and Gas Tectono-sedimentation studies suggest the
presence of various petroleum systems in Andaman basin :
• Deeply buried thermogenic system in a ponded forearc.
• Thermally induced petroleum system around the volcanic arc and
• Biogenic/shallow gas system
• Basins which are form due to convergent plate movement were have good
hydrocarbon potential if organic carbon content and thermal maturity are
satisfied. And Andaman-Nicobar basin lies in this category.
• In South Andaman and outcrops of Baratang formation are reported to
have volcanoes associated with oil and gas
• Gas discovered from Middle Miocene Limestone in AN-1-1.
• AN-32-1 well gave a silent indication of Minor Gas from lower Miocene

13. AN-32-1 & AN-1-1

14. • The total organic carbon (TOC) ranges from 2.4% & 5.2% for
Cretaceous to Oligocene Shales and Claystones.
• In the Andaman Islands, the reservoir rock is conglomeratic and
pebbly at places, with alternating silty sand and shale or fine to
medium grained massive sandstone at other places.
• Sandstone reservoirs appear to be restricted to the middle Miocene.
• But drilling results indicate that the main reservoir is carbonate from
middle and lower Miocene
• A large number of anticlinal structures within the cretaceous-
Oligocene sequence with fairly good source and reservoir facies, from
excellent entrapment conditions

15. Thermal & maturation history in deep water of Andaman-
Nicobar basin

16. Stratigraphic traps
• Pinch out of beds of upper Miocene sequence
• Possible slump and turbidite sands in upper and middle Miocene sediments
• Possible carbonate reefs in middle Miocene sequence
• Shale diapirism in lower Miocene
• The stratigraphy of onland basin has been derived from the surface geological
mapping on various islands along with data obtained from 14 shallow wells.
• The data obtained from 14 exploratory wells drilled in the offshore region has
been considered for evolving the generalized stratigraphy of the basin
• Information on subsurface stratigraphy has been obtained by exploratory drilling
of 11 wells in eastern offshore and 1 in western offshore.
• Out of 12 wells, 8 wells ended in pre-Neogene section and remaining wells at
different levels within the Neogene section.

18. Exploration status
• ONGC commenced exploration activities in 1959 by initiating geological mapping.
• 5433 Sq.km area is covered and 646 LKM and detailed geological mapping has been
done.
• Geophysical Survey in offshore by ONGC initiated in 1977 and they cover about 6370
LKM of 24 fold CDP
• In Eastern and Western Andaman they covered 1898 LKM of 24 fold by GSI in 1979, and
10,039 LKM of 48 fold in 1982
• Followed by 2426 LKM of 24 fold in 1988 and 2831 LKM of 72 fold data in 1990 in the
areas of East and South of Andaman
• Indications of gas from Early Miocene sediments were recorded in a number of wells.
• Gas discovery from Middle Miocene limestone in well AN-1-1 proves that hydrocarbons
have been generated in the Inter-deep basin of east Andaman shelf.

19. DGH Exploration
• They acquired about 7906 LKM of high resolution seismic data from
1997-2001
• The geophysical data acquisition till date by
• ONGC – 27356 LKM
• OIL – 201 LKM
• DGH – 9398 LKM
• In addition the gravity survey covers about 7314 LKM and Magnetic
survey 17775 LKM
• DGH also carried out satellite gravity survey over Andaman offshore
area of about 0.292 million Sq.km

20. Exploratory wells and NELP series
• In 1980 the first exploratory well was drilled, results in discovery of gas
with a flowing rate of 1,80,000 cubic meter per day from middle Miocene
limestone.
• Total 15 wells drilled in Andaman offshore (1-western and 14 in eastern
Andaman)
• Gas indication have been traced from Early Miocene sediments in almost
every well
• 2 blocks AN-DWN-2002/1 & AN-DWN-2002/2 offered in NELP-IV to ONGC
and another 2 blocks as AN-DWN-2003/1 and AN-DWN-2003/2 under
NELP-V awarded to ONGC and another to ENI-ONGC-GAIL
• NELP-VII offered 1 block

22. Hydrocarbon potential
• Mud volcanoes with associated oil and gas shows are reported from the
outcrops of the Baratang Formation of the Middle and South Andaman.
• Gas discovery from middle Miocene limestone in well AN-1-1 proves that
hydrocarbon generation in the Inter-deep basin of east Andaman.
• Minor gas indications observed from early Miocene of AN-32-1
• Kerogene type II and III presence in pre-Neogene have been indicated by
the well AN-63C-1
• On the basis offset basins of same geological setting this basin is
considered to be the commercially viable hydrocarbon (highly potential)
area but not yet drilled for production

24. Gas hydrates in Andaman region
• The occurrence of a gas hydrates is conditional from the presence of
the Bottom Simulating Reflector (BSR). Assessment of their potential
is one of the most controversial questions in the scientific study of
hydrocarbon generation.
• A BSR is a reflection that roughly parallels the seafloor reflection,
likely caused by the contrast between an overlying gas hydrate and
underlying gas-saturated sediments

25. ?