Future Petroleum Play in North Sumatera Basin: Volcanic Tuff Play

The North Sumatra Offshore (NSO) block is located in offshore of the Special Region of Aceh, approximately 100 km from the shoreline of Lokseumawe city which is part of the North Sumatra Basin, and it has been explored since 1980. Since 1997, this block has been produced, however recently, oil and gas production drop significantly. In order to locate the prospective hydrocarbons to enhance the number of reserves in the NSO block, a comprehensive exploration study is required. The exploration well NSO-S2 was drilled at the end of 2022, and it was successful in discovering gas resources in the Keutapang Formation and the Tampur Formation. Drilling revealed interesting geological conditions in the form of volcanic tuff, which could develop into a new hydrocarbon play that has not been discovered in the North Sumatra Basin before. From the results of the analysis of the NSO-S2 exploration well drilling, it was found that there was an alternation of volcanic tuff and claystone. The tuff deposited in the Malacca formation has physical characteristics of white, brownish white, yellowish white, brittle, conchoidal, medium hardness, composition of pyrite and volcanic ash cement, and the presence of oil show. Besides that, based on the Chromatograph, the lithology has a pressure of 767. 54 psia with a draw-down mobility of 1. 52 md/cp. The data analysis results indicate that volcanic tuff is potentially suitable as a reservoir rock due to the appropriate permeability and porosity properties. Based on cutting observation and subsurface analysis, the discovery of the potential for this new play can provide insight into the petroleum system in the Volcanic Tuff play, which is believed to have a large potential for hydrocarbon reservoirs. This invention of petroleum play potentially increases future opportunities for the exploration of hydrocarbons in volcanic rocks in the North Sumatra basin.