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Offshore: The new gas frontier of Bangladesh?

BADRUL IMAM
THIS article is about the prospect of finding gas fields in the Bay of Bengal, and is based on the recent data gathered through exploration by India and Myanmar in the Bay.
Offshore oil and gas exploration has been carried out in shallow waters worldwide for many decades. It is not very long ago that the explorations extended into the deep sea in several countries. The reward seemed phenomenal, for some at least, as the deep-water offshore unearthed so many major gas and oil deposits.
Bangladesh recently opened up its deep-water blocks to international oil companies (IOC) for the first time. There is almost no geological data available on the deep sea of Bangladesh, and this makes it very difficult if not impossible to make a reliable judgement on its oil and gas prospect.
However, a reasonable inference may be drawn on the basis of the results of the exploration in the neighbouring area. Both India and Myanmar began oil and gas exploration in their respective offshore zones for several years ago and both have been successful in discovering large gas fields in their areas. Will Bangladesh also find its deep sea emerging as a new
gas frontier?
The Bay of Bengal is a large sea off the coast of Bangladesh, India, Myanmar and Sri Lanka. It has a maximum depth of about 4.000 meters. In offshore oil gas exploration, water depth up to 400 meters is considered shallow, while anything deeper is deep water. Explorations in deep water are generally carried out up to a depth of about 2,000 meters. In the deep water of the Bay of Bengal. Bangladesh has disputes over border demarcation with India and Myanmar. Bangladesh claims that both its neighbours have encroached upon its deep-water territory and conducted exploration.
To the west and southwest of the Bangladesh deep-sea blocks lie Indian deep-sea blocks D6 and D4. Major gas discoveries in these blocks have changed the way the Bay of Bengal has been looked at. especially by the major IOCs. Gas fields discovered in the deep-water block D-6 off Andhra Pradesh are among the largest in India.
Offshore exploration is technologically more challenging as well as costlier than onshore exploration, and it is far more so in the case of deep-water. The big gas discoveries in block D-6 were made by the Indian company Reliance Industries Limited (RIL), which has already started producing gas from these fields. It has
been forecasted that the production from these fields will nearly double tire total Indian gas output in about a year.
The interpretation on the origin of the deep-sea gas as given by Indian geoscientists has been a subject of much interest -- basically for two reasons. Firstly, according to RIL geologists, the gas found in the deep-sea blocks is not conventional thermogenic gas but unconventional biogenic gas. Secondly, the gas accumulated into a commercial deposit not by a conventional process known to petroleum geologists but by an unconventional process involving "gas hydrate." What is gas hydrate, and thermogenic and biogenic gases?
Both thermogenic and biogenic natural gases have the same quality, but differ radically in their origin. Thermogenic gas is the natural gas formed from organic matter in the rock under the influence of heat deep inside the earth. Most of the world's gas deposits, including the ones in Bangladesh, are thermogenic in origin, and are referred to as conventional naturalgas.
Biogenic natural gas, on the other hand, requires no heat, and is generated from organic matter by the action of bacteria at a very shallow depth. Therefore, in areas where geothermal gradient is low -- meaning there is less heat available underground - biogenic gas still holds promise. Because of the low geothermal gradient, thermally mature rock is not easily found underground, which is one drawback for the prospect of gas in Bangladesh. Therefore, the existence of biogenic gas in the deep-water neighbourhood of Bangladesh is promising in that respect.
Even more unconventional is the
geoscientlsts' Interpretation regarding how biogenic gas eventually accumulated into large gas deposits through the formation and destabilisation of "gas hydrate." Gas hydrate is an ice-like solid formed by the combination of gas and water molecule in the ocean floor and in polar region. The RIL geoscientlsts argued that biogenic gas was converted to gas hydrate at or near the bottom of Bay of Bengal. Later, the gas hydrate was converted back to natural gas and was trapped in nearby reservoirs. This is how the deep-sea gas deposit off the Indian shore was formed. This process is likely to have worked in other deep-sea areas of the Bay.
Geologists believe that should the theory be correct, it will raise the prospect of gas manifold in the deep-water of the Bay. This assumption is based on the fact that large deposits of gas hydrate were recently discovered under the Bay of Bengal floor during explorations carried out by US and Indian geoscientists. The deep-sea areas off Andhra Pradesh, Orissa and Andaman Nicobar Island are the most abundant gas hydrate sources. Interestingly, these areas surround the Bangladesh deep-sea zones.
In a recent fact finding visit to Bangladesh, British Petroleum (BP) geoscientist Jonathan Evan, while talking to this writer, expressed his opinion on the prospect of gas in deep water off Bangladesh. "There is too little data available on deep-water offshore blocks of Bangladesh and one can only make conjectures on what is there. We tend to believe that the Bangladesh deep water offshore has good prospect of biogenic gas. The recent experiences of BP in deepwater gas discoveries of biogenic origin
off Egypt led us to believe that similar environment may have prevailed in the Bay of Bengal in geologic past and hence is the optimism," he said.
Even more interesting are the big gas findings in Myanmar offshore in recent times. The very large gas fields off the Arakan coast are just about 100 km south of St. Martin's Island in Bangladesh. These gas discoveries, along with those on the Indian side, have raised the interest of gas explorers to venture out into Bay of Bengal.
From the above it appears that geoscientists point to unconventional biogenic gas as a bright new prospect in
the deep-water Bay of Bengal. Whether similar new gas frontiers will emerge in Bangladesh offshore blocks is a million dollar question that nobody can answer at present.There are too little geological data on Bangladesh deep-water offshore blocks to make a precise judgement. However, the neighbours' discoveries have raised many possibilities. Only intensive exploration by companies with high-tech high-cost capabilities can actually offer a definitive answer. Dr. Badrul Imam is Professor. University of Dhaka and Visiting Faculty, University of Regina, Canada