Publications

The offshore North Sumatra Basin (NSB) is a relatively immature exploration province with supergiant potential. It has strong parallels to the mature, onshore part of the NSB, which has been a major hydrocarbon province for more than a century. In the first century of exploration, a number of significant discoveries accounted for 6BBOE of hydrocarbon reserves, mostly gas. During this time, approximately 500 wildcat wells were drilled in the onshore portion of the basin. In contrast, only 42 wells were drilled in the offshore portion of the basin, which comprises more than 75% of the area. These wells were drilled in shallow water in the 1980s, and resulted in minimal new reserves additions (again mostly gas). In the past 30 years, less than 0.5 BBOE have been discovered, and, between 2005-2016, only 4 offshore wells were drilled. Partly on the basis of these negative results, the United States Geological Survey etimated that there were only 0.3BBOE yet to find in the basin (USGS, 2010). Most of these unproven reserves were assumed to be gas, based on the exploration track record. As a result, the region has been considered effectively creamed by all conventional metrics. And thus ends, for practical purposes, the story of exploration in the North Sumatra Basin. Or does it? To quote Sir Francis Bacon (The Advancement of Learning, 1605, Book II, vii, 5), "They are ill discoverers that think there is no land, when they can see nothing but sea." Recently acquired 3D marine seismic data show that all of the prolific trends in the onshore part of the basin extend into the offshore, and that the undrilled potential of these plays may exceed the discovered volumes to date. Moreover, there is a strong likelihood of oil as well as gas charge, both of which add a component of true greenfield exploration to this supposedly mature, but massively underexplored, province. This paper reviews the fascinating exploration history of the region from the dawn of petroleum exploration to the advent of modern technology, characterizes its petroleum systems with specific reference to the new and the historic data, and demonstrates its future potential in the offshore portion of the basin. The key play is prolific stratigraphic traps in Miocene carbonate build-ups (Peutu Formation) on Oligo-Miocene syn-rift horst blocks.