Background
Nepal lies in the central Asia between China to the north and India to the south. Southern Nepal occupies some 20 to 40 km wide Terai plain (Indo-Gangetic plain) about a few hundred meters above sea level. The Terai and the Siwalik areas are in the foreland of the Nepal Himalaya and are known for sedimentary basins with considerable thickness. Several sedimentary formations of the basins could have generated petroleum and could be located in suitable structural traps. Terai and Siwaliks are thus target areas for hydrocarbon exploration. This part of the country is covered by road network, electricity lines, etc., and is the most accessible region in Nepal.
It is notable that oil and gas seeps have been observed to the north of Main Boundary Thrust (MBT) in different parts of the country from time immemorial. These seepages, as in Dailekh, western Nepal, were subjected to only preliminary analysis in the sixties, but extensive geochemical studies were done in 1993. One of the gas seeps in Dailekh is shown on the back page.
Systematic petroleum exploration activities began only in 1997. The Department of Mines and Geology (DMG) has conducted Airborne Magnetic Survey in 1978-79 over the Terai and Siwalik belts of the country, covering an area of 48,000 sq. km with the help of IDA/World Bank. The survey has shown encouraging results. The Government of Nepal then established a separate unit, “Petroleum Exploration Promotion Project,” in 1982 to promote and monitor the exploration works in Nepal.
Exploration History
A series of geological, geochemical, and geophysical works were carried out after the completion of the aeromagnetic and seismic reflection survey in a regional grid pattern by the Compagnie Générale de Géophysique (CGG) and Petro-Canada (over 3,000-line km.
Hunting Geology and Geophysics Ltd. conducted a photogeological study over a 60,000 sq. km area of southern Nepal. It has been useful to establish the structures in the Siwalik belt.
Terai and Siwaliks have been divided into 10 exploration blocks, each of approximately 5,000 sq. km in area. These blocks were opened for bidding exploration acreage in 1985 for the first time.
Shell Nepal B.V. (1986-90) carried out exploration works in Nepal (Block 10), including geochemical study of seep samples. It has also acquired gravity and seismic surveys (over 2,000-line km) in a close grid pattern. The company had drilled an exploratory well (TD 3,520m) to test the hydrocarbon potential of a seismically defined structure. The hole was dry and did not penetrate up to the basement. The result obtained from the drilling has created a valuable database for the exploration venture. Because oil and gas fields of Bangladesh and Assam oil field in India are not far from Block 10, Biratnagar.
Hydrocarbon Occurrence
In the regional hydrocarbon occurrences, it is noteworthy that the Ganga Basin of Nepal is on a trend with the Potwar Basin to the west in Pakistan and the Assam Basin to the east in India. Both of which have similar geologic histories to Nepal and have proven to be hydrocarbon-bearing with a long history of successful exploration and production operations.
In Nepal, oil and gas seeps occur in the western part of the country. The geochemical analysis of these seep samples indicates that these oil and gas have a geological origin from a mature source rock.
Hence, the presence of oil and gas seeps in western Nepal, along with the existing analogous basins of Potwar and Assam, and all the available technical data including the recent drilling data of the Biratnagar well, lead us to believe in the possibility of hydrocarbon occurrence in Nepal.
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