Publications

In the past, most exploration companies were not interested to develop their biogenic gas discoveries due to economic reasons. But in the last decade, there has been a growing interest in gas exploration, which includes both thermogenic and biogenic gas. This paper describes how to evaluate and explore for biogenic gas using conventional exploration processes. Biogenic gas has become increasingly important due to high energy demand, such as in fuel for power generation and in the fertilizer industry. Gas reserves including those of biogenic origin are currently attracting a higher price with a positive impact on gas project economics. There has been recent success in conventional biogenic gas exploration in the northwestern part of East Java Basin, where two commercial biogenic gas discoveries have been made in the Lengo (1998) and Mustika structures (2015). These discoveries are located over the Bawean Arch, where there had been no commercial discoveries for the last 27 years since the discovery of Kepodang biogenic gas field in 1971. Gas has been trapped within the Miocene Kujung I carbonate platform that was deposited over the Bawean Ridge. The Kujung I carbonate reservoir development was controlled by sea level fluctuations. Reservoir properties were enhanced when the sea level dropped, followed by periods of surface exposure and karstification. The source of the gas are coal layers and carbonaceous shales of the Kujung III Formation that was deposited in the Muriah Trough. The trough was developed at the edge of the Karimunjawa Arch with an average basement depth of less than 7,000 feet. The geothermal gradient in the trough is low and it is expected that the high organic carbon content layers would have been given rise to biogenic gas/ methane. Important factors for generating biogenic gas in the shallow basin are anoxic environment, presence of organic matter, low temperature and accommodation space. Since only three gas fields have been discovered in the area to date, the Muriah Trough - Bawean Arch trends remain as an attractive exploration province. The occurrence of high CO2 gas is the main exploration risk because of abundant volcanic activity in this area.