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|ALTERNATIVE AND UNCONVENTIONAL HYDROCARBONS|
Prospects in East and North-East India
||By A. K. Dwivedi, GGM & Basin Manager, ONGC Limited|
Energy is the most critical input for the growth of a nation and is the principal force in driving our society and industries. The development of a nation is very much contingent on meeting its energy demand and two principal socio-economic factors that drive the pace of energy demand are population and domestic production. The ever increasing gap between demand and supply has become a perennial headache for planners worldwide, more so in India.
With its 1.24+ billion population and the blooming economy seeking more and more energy, that too at a cheaper level, we have an unenviable task at hand which is drastically different from those of developed countries like USA. In the last few years only the price of petrol has increased alarmingly. The ever increasing import burden and the danger that lurks need no other yardstick for easy comprehension. A look at the worldwide scenario of LNG market with prices touching as high as 22$ and the electricity produced at Rs.15 per unit also puts 2012 as a turning point in history which may decide our survival.
In India, though bulk of the energy need was fulfilled by non-conventional energy sources like wood, animal wastes & agricultural residues, last few decades has seen rapid rise in the use of fossil fuel and presently more than 70% of our energy need is met by these energy sources. As far as oil is concerned, we are the 5th largest consumer in the world and with a target of growth rates of 8% over the coming years the country’s energy consumption is expected to be double. In primary energy supply.
Natural gas has experienced the fastest rate of increase in recent years and is fast expanding the gap between demand and supply. Hence a country like India, where more than 70% of our energy need is mitigated from importing, look for alternate and unconventional source of energy has become an important thrust area.
So, what are those thrust areas? Or to put in a simple way, what are those other sources of energy where from we can exploit hydrocarbon so as to satisfy the ever increasing energy appetite of the country. Simple answer would be looking for those energy sources, which earlier were not thought of as a potential due to many reasons like lack of proper technology, economic viability etc. etc.
One of the most important resources, which is of immediate commercial interest to us, is CBM or Coal Bed Methane. Coal, the most abundant hydrocarbon in the world is a major source of methane gas. Because of its large internal surface area, coal stores between 6-7 times more gas than the equivalent rock volume of a conventional gas reservoir. Moreover, we have vast reserves in the country and is the 3rd largest producer of Coal with a global production share of almost 6%. Moreover, Government of India has taken initiatives and approved a CBM exploration and exploitation policy for the country. Commercial production of CBM has already started and going by the estimates, CBM production could be of the order of 38 million cubic meters per day for about 20 years at peak production level.
Another important resource of alternate hydrocarbon energy is Gas Hydrates. Naturally occurring gas hydrates are ice like compounds in which gas molecules, methane in most cases, are engaged 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.
Subsequently 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 can be 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 source of 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. Realizing its national obligation and possibility of exploitation of gas hydrates as a future business opportunity, ONGC has taken up the job of detailed planning/implementation of various aspects of gas hydrate exploration and exploitation. 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 and 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 Andaman-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 and other geo-scientific information (bathymetry structure, thickness of hydrate stability zone (HSZ), rate of sedimentation, depositional set up etc.)
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 calibration 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 comprehensive techno economic perspective can be evolved to initialise hydrate exploration operation in Indian environment prior to their cost-effective exploration.
Gone are the days when shale was only thought of as a source rock. Better knowledge with advancement in technology has already made the source rock as a reservoir too & terms like ‘Shale Gas’, ‘Shale Oil’ has started making headlines. As part of the bundle of unconventional energy resources, gas from shale can make a significant contribution to the global energy supply.
Apart from the United States and few other countries, shale gas resource, although believed to be both large and wide spread, have not been quantified on a national basis for most countries. The global shale gas resource endowment is about 16,110 TCF or 456 TCM, compared to 187 TCM for conventional gas. It is assumed that nearly 40% of this endowment would be economically recoverable.
Until recently, the shale gas focus was mainly on North America, but today the interest towards shale gas is spreading around the world. Three European basins are worth mentioning namely, Alum Shale in Sweden, the Silurian Shale in Poland and Mikulov Shale in Austria. In US, there was a sharp change in US Shale Gas reserve estimate.
Dry shale gas production in US has increased from 1.0 TCF in 2006 to 4.8 TCF in 2010 while wet shale gas has increased to 60.64 TCF by the year-end 2009.
According to geologists, there are more than 668 shales worldwide in 142 basins. At present, only a few dozen of these shales have known production potentials, most of those are in North America. This means that there are literally hundreds of shale formations worldwide that could produce natural gas. The potential volumes of shale gas are thought to be enormous and this is likely to change the natural gas markets worldwide.
India has very little domestic gas production, and almost all of it is based on young rock in the offshore. In India, the shale gas will be primarily targeted at Cambay basin, Assam-Arakan basin, Damodar Valley, KG basin and Cauvery basin. In Karanpur, at Raniganj, ONGC has drilled first well out of the four wells planned. The initial results are encouraging but one has to wait for some more time to ascertain whether shale gas production is commercially viable or not. According to Schlumberger, hired by ONGC, Shale Gas reserves in India would be anywhere between 600 TCF to 2000 TCF. Realizing the huge potential of shale gas, the Government of India is likely to offer shale gas exploration for the first time.
In Cambay basin huge thickness of shale ranging from 400 to 1000 meter can be a good target. The Cambay shale is divided into Upper Cambay shale and Lower Cambay shale and both have potential to produce shale gas. In Cambay shale the average clay percentage is 38% and quartz percentage is 35%. The kerogen is of type III, and the high TOC value 1.5-4% and maturity between 0.9-1.0 at 800 meter depth. Oil India has also planned a project to drill two wells in Assam-Arakan basin at a cost of USD 25 Million. It is planned to create a platform to use the experience of US to understand and exploit shale gas plays in India.
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