Gas Hydrate Occurrence in the Krishna–Godavari Offshore Basin Off the East Coast of India
a report by
MV Ramana and T Ramprasad
National Institute of Oceanography, Goa
India is blessed with adequate reserves of coal and hydro resources, whereas the conventional hydrocarbon (oil and gas) reserves so far estimated are inadequate to meet its growing demand. The latest estimates indicate that India has around 0.4% of the world’s proven reserves of crude oil and natural gas; against this, domestic consumption is estimated at 2.8% of global consumption. The balance of recoverable reserves, estimated at the beginning of 2001, is 733.70 million metric tonnes (MMT) of crude and 749.65 billion cubic metres (bcm) of natural gas. Crude oil demand is currently about 146MMT against domestic production of only 34MMT. Similarly, the natural gas demand is currently about 179 million metric standard cubic metres per day (MMSCMD) against domestic supply of about 80MMSCMD. India’s crude oil import dependency is likely to increase from the current level of 72% to 90% by 2025. India’s domestic natural gas demand will show a breakaway growth with demand rising to 200mm cubic metres per day (cmpd) from the current 70mm cmpd. However, the additional gas production from new finds, such as that made by Reliance Industries in the Krishna–Godavari offshore, may still not be able to meet the entire requirement, since the power sector and fertiliser units will likely consume >74% of the projected demand, and the 26% balance will be consumed by other industries, transport and domestic use. This huge demand needs to be met either from imports or by an increase in domestic production and switching to non-conventional energy fuels. One such non-conventional fuel is methane gas stored in gas hydrate deposits. The significance of this gas hydrate is that it is abundantly available in the shallow marine sediments of slopes, and on dissociation one cubic metre of gas hydrate yields nearly 164 cubic metres of pure methane gas and about 0.8 cubic metres of fresh water. In 1996, the Ministry of Petroleum and Natural Gas (MoP&NG) of the Government of India initiated an ambitious plan to explore gas hydrate deposits within the Indian continental margins to partly meet the projected supply–demand gap of fossil fuels. Continuous efforts of the Indian scientific community and oil industry culminated in the identification of the most probable areas for detailed exploration. One such promising
MV Ramana is a Geophysicist at the National Institute of Oceanography and has led several scientific research programmes including offshore mineral exploration, gas hydrate research and continental margin investigations. He is a member of the Technical Committee and Core Group of the Indian National Gas Hydrate Programme and a recipient of the National Mineral Award for his outstanding contribution in the field of geophysics. He has published more than 75 scientific articles. Dr Ramana is a Fellow of the Geological society of India, the Indian Geophysical Union and the Association of Geophysicists and a member of the American Geophysical Union.
E:
ramana@nio.org
T Ramprasad is a Geophysicist at the National Institute of Oceanography. Since 2006, he has led the gas hydrates research group. He specialises in marine geophysical studies for the exploration of gas hydrates and the structure and tectonics of the northern Indian Ocean. He participated in several scientific cruises with more than 1,200 days at sea. He is a member of the Geological Society of India, the Indian Geophysical Union, the Association of Geophysicists and the American Geophysical Union.
area is the Krishna–Godavari (KG) offshore, on the eastern continental margin of India (ECMI). Some results of this initiative under the Indian National Gas Hydrate Program (NGHP) are presented in this report.
Introduction
Gas hydrate has received global attention as a possible alternative non- conventional energy resource due to its tremendous holding capacity for the pure form of methane under suitable low-temperature and high- pressure conditions in the permafrost and continental slope areas. Gas hydrate, or clathrate, is a crystalline molecular complex formed from mixtures of water and suitably sized gas molecules. Water crystallises in the cubic crystallographic system and forms a cage-like structure around a smaller ‘guest molecule’ such as methane, ethane, propane, isobutene, normal butane, nitrogen, carbon dioxide or hydrogen sulphide, of which methane is the most common.2,3
The amount of natural gas estimated
from the world’s gas hydrate accumulations, although speculative, is at least 100,000 trillion cubic feet (tcf).4
By contrast, the conventional
natural gas accumulations for the world are estimated at approximately 440 trillion cubic metres (tcm) only. Gas hydrate fields the world over have been initially recognised from the detection of anomalous acoustic reflections on the industry-acquired conventional multichannel seismic (MCS) reflection data. This anomalous reflection is popularly known in the geoscientific community as the bottom-simulating reflection (BSR). The likely occurrence of gas hydrate has been further established with gas hydrate stability zone (GHSZ) thickness maps, geochemical proxy indicators such as the sulphate–methane interface (SMI) and chloride anomalies and methanotrophs and methanogenes and their dynamics at different depths in the gas-hydrate-bearing marine sediments.
Research activity in the field of gas hydrate has been intensified primarily to assess the amount of pure methane present in the gas hydrate, understand the geohazard caused by the sudden release of gas from gas hydrate when it is affected either by changes in pressure and temperature or any tectonic disturbance and address its impact on climate due to the mixing of methane gas with the atmosphere as well as the ecology of the environment below the water and subsurface. Recent gas hydrate expeditions (Hydrate Ridge, Oregon Margin, Cascadian Margin, Gulf of Mexico, Arabian Sea, Bay of Bengal and Andaman Sea, South China Sea, East Sea) aboard JOIDES Resolution (JR) have similar goals, such as characterisation, mapping of spatial and temporal extent, quantification, concentration estimation and composition, measurement of gas hydrate morphology within the sediment and measurement of the in situ properties of the matrix. The BSR, one of the primary proxy indicators in gas hydrate detection in general, can be recognised on the MCS records as a pseudo reflector that mimics the seafloor topography with a polarity reversal, cross-cuts different lithological boundaries and associates with amplitude blanking above and below it. Furthermore, the BSR also indicates a depth below which the hydrate destabilises. Some of the best-known major oilfields in the world (for example the Gulf of Mexico,
22
© TOUCH BRIEFINGS 2010
Regional Focus – Asia
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148