Abstract

Forearc basins result from plate convergence. These basins are situated offshore between an outer-arc high and the mainland. Historically, these regions have not been considered important petroleum provinces partly because low heat flow may limit significant thermal hydrocarbon generation.

The Simeulue forearc basin extends between Simeulue Island and northern Sumatra. It is a frontier shallow shelf area with few wells and no wells in the basin center; therefore, it is studied using geophysical data and geologic surface samples. Multichannel seismic data show bright spots above potential hydrocarbon reservoirs in carbonate buildups. Amplitude versus offset analyses indicate the presence of gas, and surface geochemical prospecting suggests thermal hydrocarbon generation. Heat flow in the Simeulue Basin ranges between 37 and 74 mW/m 2, as deduced from one-dimensional petroleum system modeling and bottom-simulating reflector depths. Two possible source rocks (Eocene and lower–middle Miocene) were assigned for three-dimensional petroleum system modeling in the Simeulue Basin. Because of a similar pre-Miocene geologic evolution of the present-day back arc and the fore arc, it can be assumed that the back-arc source rocks also occur in the fore arc.

Modeling based on two heat-flow scenarios (40 and 60 mW/m 2) reveals that oil and gas generation is possible within and below the main depocenters of the central and southern Simeulue Basin. This study shows that deep burial (>6 km [>3.7 mi]) of source rocks can compensate for low heat flow. Therefore, forearc basins may be more prolific for hydrocarbons than previously considered, and each forearc basin should be studied carefully to evaluate its hydrocarbon potential.

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